This PDF file contains the front matter associated with SPIE Proceedings Volume 10827 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Measuring objects with drastic texture variation is a big challenge for fringe projection profilometry (FPP) systems. In this paper, the reasons why textures on measured objects' surface influence the measurement accuracy are thoroughly analyzed and an effective phase error compensation method is proposed. Due to the existence of various random noises, the reconstruction accuracy will be negatively affected by the textures with different reflectivity. As an intrinsic feature of digital cameras, random noises be hardly removed by mathematical solutions. In this paper, it is mathematically proved that image pixels with the same fringe modulation have the same noise variance and the same phase error variance. With the aid of fringe orientations calculated in the phase map, pixels which satisfy the following two conditions are picked out as a group: 1. They should have the same phase. 2. They have almost the equivalent modulation values. Then the phase values of this group of pixels are averaged and this mean phase is the compensated phase value. Experiments demonstrate that the proposed method can effectively reduce phase errors caused by random noises and textures with small reflectivity.

Ionic polymer–metal composite (IPMC) cantilever actuator demonstrates significant bending deformation upon application of excitation voltage across electrodes without external load. In the present work, the non-contact digital image correlation (DIC) and a digital microscope were used to investigate the micro-scale displacement and strain distributions on the cross section of the actuator under excitation voltages, according to the low mass and film properties of IPMC material. The target surface of the fabricated IPMC sample with Pt electrodes was roughened with fine sandpapers to prepare an appropriate speckled surface. The experimental results indicate that longitudinal normal strain is linearly distributed along the thickness direction and strain gradient of longitudinal normal strain varies linearly with electric field. The longitudinal and transverse normal strains decrease with the increase of the frequency of the excitation voltage. Moreover, due to water loss of the sample in air, the IPMC actuator demonstrates contractive deformation when exposed in the air. The micro scale DIC technique has been proved to have excellent accuracy over a large range of strains, thus is very powerful for mechanical analysis of IPMC materials.

Atmospheric pressure plasma technology has been presented as an effective tool in relieving or removing subsurface damage induced by previous mechanical machining process. However, the surface morphology evolution and mechanism during removing the subsurface damage using atmospheric pressure plasma processing after grinding to remove the subdamage is rarely reported. In this research, this procedure is studied based on experiments and measurement. Even if some unique properties of atmospheric pressure plasma processing are observed, such as particle exposure. From the mechanical machining to atmospheric plasma blasting, the R_PV value increase from 1.338 μm to 1.361 μm due to some singular deep cracks that are not fully healed or filled by the abrasives. Corresponding peak-tovalley and RMS roughness evolution is investigated as well. It is revealed that the atmospheric pressure plasma process may end up with a planar surface depending on the damage removing. Density of the damage has more significant effect on the roughness evolution than damage depth.

According to the requirement for high precision surface measurement in the special conditions, a Linnik type measuring system with long working distance was built up based on white-light microscopic spectral interferometry. The influence of the transparent medium on the interferogram was minimized by the optical path compensation in the reference beam of the interferometer. Surface profile and film thickness can be obtained accurately after the optical path compensation and nonlinear phase error correction. The measuring results with and without transparent medium were compared to show the feasibility of the proposed methods, including displacement, profile and film thickness measurement. And experiments on the surface with complex profile and the film standard showed that the system still kept the nanoscale accuracy through transparent medium.

Digital image correlation (DIC) combined with an optical microscope has been used to realize the micro scale deformation measurement; micro-scale speckle pattern film was fabricated by spinning an epoxy resin and powder, and transferred to the surface of a test specimen. Generally, measurement accuracy of a 2D DIC will be affected by the small out-of-plane displacement of the test specimen. However, a telecentric lens is not convenient to be used in micro-scale digital image correlation to minimize the measurement displacement error. Thus, measurement error due to geometrical lens aberration, or lens distortion, should be corrected to overcome this problem. Camera calibration including lens distortion is considered in this paper. A corresponding distortion model was constructed and the distortion coefficient was determined by a rigid-body translation experiment using the fabricated micro speckle patterns. The distortion image was calibrated using a first-order aberration function. The results show that the relative error of the rigid-body translations was reduced 50%. Therefore, the proposed method can effectively correct the lens distortion under the large-magnification microscope.

Observations of marine boundary layer trace gases vertical column density (VCD) over the offshore sea area near the Yellow Sea were conducted by ship-borne Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) carried by a Chinese oceanography research vessel, XiangYangHong 08, during an offshore observation campaign, from 13 September 2015 to 18 September 2015. During the offshore observation campaign, the ship-borne MAX-DOAS system made a sailing measurement over the offshore sea areas near the Huangdao district, Qingdao city from 8:00 to 13:00 on 16 September 2015. Observation results of sailing measurement are shown in this paper. By combining geometric character of monitoring area and weather condition, it can be concluded from the sailing measurement results that the geographic conditions have a significant influence on offshore sea boundary layer trace gases content. The sailing measurement showed that the Huangdao offshore sea area boundary layer had much more NO₂ and O₃ content than other sea areas because the Huangdao offshore sea area is near urban area with surrounding high trace gases content which may be susceptible to human activities, such as traffic influence.

Observations of traffic trace gases near-surface concentration over a busy urban road in Qingdao were conducted by long-path differential optical absorption spectroscopy (LP-DOAS). During the observation period, the LP-DOAS system made long-term trace gases measurements over the Haier Road in Laoshan District, Qingdao. And a camera was placed next to the LP-DOAS system to record the traffic condition every day. The relationship between the trace gases measurements results and the traffic flow is presented in this paper. The weekly characteristics of the trace gases due to traffic influence are further studied in this paper. Using typical data on January 3 and March 22, 2018, the NO₂ concentration is under a strong positive correlation with the traffic flow, and O₃ concentration is under a negative correlation with the traffic flow. The correlation coefficient between NO₂ measurements and traffic flow from 7:00 to 18:00 is 0.86. The comparison of daily measurements during a week showed that the working days had much more trace gases content than the weekend which may be affected by the different traffic condition among working days and the weekend.

An infrared imaging spectrometer based on a variable gap interferometer is introduced, which is working in 7.7μm~14μm, and often used in spectral measurement, camouflage target detection and gas component identification. In this paper, the wedge prism shapes processed by grinding and diamond knife turning is compared, which affects the phase distribution near zero phase of the interferogram, and results in the difference of spectrum in the result. Finally, the turning process with less damage to the sharp edges was selected. An adjusting device and monitoring software are designed to ensure the symmetry of the wedge angle of the interference cavity with variable gap, so that two sides of the interferogram are sampled at equal intervals. The working mode is designed as the interferometer’s linear translation scan inside the imaging spectrometer. This working mode can reduce the volume of the system, and decrease the noise caused by the nonuniformity of the FPA response, improving signal-to-noise ratio. Stepper motor, rail and slide block are used to realize uniform reciprocating scanning. Finally, some measurement results using this infrared imaging spectrometer are presented.

The focus variation microscopy is widely used and researched in both industrial and academic field. But the 3D construction quality of surface topography is affected by the noise, the double peak value, and the discontinuous surface, and so on. A simulation method for focus variation is proposed based on the physical model of optical imaging and the Point Spread Model(PSF). At first, the linear relationship between the blur factor σ of Gaussian function and the defocus distance δ is deduced which is called point spread parameter λ, then, considering the positive correlation between blur factorσ and blur degree, the difference between the real defocused image and the calculated image by Gaussian convolution operation to real captured focused image is shown. It is used to the objective to computed the accurate value σ and the spread parameter λ. At last, the difference between focus measure valued of real image sequence and simulation image sequence is used to verify the method. The simulation method is a judgement basis for focus measurement, the single peak of focus curve, and the identification of high-frequency noise.

The observations of marine aerosol over the Yellow Sea near Qingdao were carried out using a ship-borne scanning micro pulse lidar (SMPL) onboard the oceanographic research vessel, XIANGYANGHONG No.8 (XYH-08). The observation campaign including anchor point observation and sailing observation was conducted from September 13th to September 18th, 2015. We acquired observation data of sailing route including aerosol extinction coefficient, the temporal and spatial variation of aerosols and clouds, and the structure of boundary layer and so on. Through the function of 3-dimensional scanning, the SMPL also provided range-height indication (RHI) and plane-position indication (PPI) of observation signals which could well reflect the distribution of marine aerosol in different directions. From the change of aerosol extinction coefficient, we successfully captured a process of sea fog occurrence.

As a core part of phase retrieval, phase unwrapping is widely used in the field of phase-based optical testing. In the past few decades, a large number of phase unwrapping methods have been proposed which can be divided into the pathdependent and the path-independent ones. In general speaking, the former is faster but more susceptible to noises, while the latter is time-consuming but more robust. In consideration of the aforementioned problems, a phase unwrapping algorithm based on iterative zonal reconstruction technique is put forward in this investigation. For a wrapped phase map with a rectangle pupil, the proposed method can directly and speedy achieve the phase unwrapping with a simply zonal reconstruction. For the case of an arbitrary pupil, the phase unwrapping is realized by an iteratively compensated zonal reconstruction with a slightly increased amount of calculation. Simulations and experiments have been carried out to demonstrate the effectiveness of the proposed method as well.

Chromatic confocal point sensors are used to measure the high-precision surface distance, and it's based on the theory of chromatic dispersion and encodes the distance between the measure surface and chromatic lens. By accurately measuring the wavelength value, it indirectly calculates the distance to object surface. The accuracy of the sensor depends on the chromatic range of the lens and the resolution of the spectrograph. It is difficult to design wide measuring range chromatic lens that meanwhile satisfies the high-precision requirement. This paper proposes an optimization method to design high-precision chromatic lens for chromatic confocal point sensors. Firstly, we theoretically study the relationship of the pin-hole diameter and the sensors' performance denoted with the resolution and signal-to-noise ratio(SNR). Then, using the optimization objective FWHM(Full Width at Half Maximum), we build the mathematical model about N.A.(Numerical Aperture), PD(Pupil Diameter) and Δf. Finally, based on the optimization method, we design chromatic lens with Zemax Software, the performance gets the accuracy 2μm in the measure range 1mm.

This paper compares two kinds of cylinder stitching algorithm: global error homogenization stitching algorithm and Legendre Fourier polynomial fitting algorithm. The former uses the overlapping regions between adjacent sub-apertures, which can obtain high accurate results but need more time on data acquisition; Legendre-Fourier polynomial fitting stitching algorithm without overlapping regions need less aperture and short measure time but lack of high frequency information. Its stitching results easily affected by the position error of sub aperture, which is more suitable for in-situ measurement.

The line-scan dispersive interferometry (LSDI) benefits from single-shot measurement in nature and has potential to perform in-line surface metrology. In this technique, the interference beam produced by the two arms of the interferometer is spatially dispersed by a diffraction grating along the rows (or columns) of the CCD pixels. In which case, a two-dimensional spectral interferogram is generated. In this paper, fringe order determination is carried out to retrieve the more accurate phase information along the chromaticity axis of the interferogram and then the height map of the tested profile can be calculated with high resolution. Two standard artefacts have been evaluated using the developed LSDI and the experimental results are compared with that of phase slope method as well as the commercial instrument (Talysurf CCI 3000), which shows that better performance in measurement noise is achieved. Additionally, the measurement repeatability is significantly improved and demonstrated within sub-nanometer range.

Since the coherent noise in the interferometric system, the method of rotated diffuser would reduce the coherence of the light beam to suppress the noise of the interference image. By analyzing the coherent noise reduction characteristics of rotated diffuser with different surface roughness, the relationship between surface roughness and the noise contrast under different rotation speeds was simulated, and the effective roughness range with noise reduction effect would be selected. It would build a noise reduction system based on Fizeau interference, and collected and calculated the noise contrast of the interference image. The effective range of σ_h/λ was 0.2~0.5 when the rotation speed was 10r/s, while the effective range of σ_h/λ was 0.4~0.6 when the rotation speed is 100r/s. The experimental results showed that the surface roughness and wavelength ratio σ_h/λ of rotated diffuser increased when the noise contrast tended to 1, but the effective range of surface roughness decreases with the increase of the rotational speed of the diffuser.

The multi-grid method is a common method for solving the transport of intensity equation (TIE). Transport of intensity equation can retrieve phase information from the directly measured intensity image. When using multi-grid method to solve the TIE, firstly, the phase distribution is directly solved on the coarsest layer. The solved phase distribution is regard as the initial value on the finest grid layer to increase the convergence speed of the algorithm. Residual error on the finest grid can be obtained, then, using the restrict operators transfer the residual error from finer grid to coarser grid, until the solution on the coarsest grid is obtained. the solution on coarser grid transfer to finer grid by using prolongation operator, until the accurate phase distribution solution obtained on the finest grid. The Simulation experiments show that this method has a better convergence rate and retrieves complicated phase with higher accuracy.

Tunable Fabry-Perot filter is an important device in optics. It is widely used in high resolution spectroscopy, laser linewidth measurement, laser frequency stabilization and so on. The filtering characteristics of the Fabry-Perot filter are directly related to the cavity length, and the performance is greatly influenced by the parallelism of the cavity mirrors. For a tunable Fabry-Perot filter with parallel cavity, it is difficult to directly measure the cavity length and determine the parallelism of the cavity in the tuning process. In this paper, a tunable Fabry-Perot filter with an automatic cavity-length stabilization and monitoring system is designed. Four metallic electrodes are deposited on each cavity mirror of the FP filter, thus to form 4 parallel-plate type capacitive sensors. With the help of a capacitance measurement circuit and a micro-controller circuit, the capacitances of the sensors can be acquired. After calibration, the mean value of the capacitances is used to determine the cavity length of the FP filter, while the differential capacitance values in two orthogonal directions are used to monitor the tilt of the cavity mirrors. A feedback control system composed by PZTs, a MCU and the capacitive sensors is therefore constructed to automatically stabilize the F-P cavity length and to adjust the parallelism between the cavity mirrors. The automatic cavity-length stabilizing and monitoring system has the advantages of high accuracy, strong disturbance resistance and high measuring speed. Experimental results prove that it can effectively measure the cavity length of the tunable Fabry-Perot filter, and can stabilize the FP filter as well.

Fourier ptychographic microscopy (FPM) is a new imaging technology developed in recent years, which can achieve a high-resolution imaging with large field of view (FOV). In FPM, the imaging retrieval quality depends on the exact position of the LED array, and there exists position errors of LED array in practice. To obtain the accurate position, this paper proposes a method of vision assisted localization to determine the coordinates of LED array, which can provide the accurate LED ray directions for improving FPM. Additionally, a multi-resolution reference is built to settle the inconsistent FOV between the FPM system and vision assisted system. The experiments are performed to illuminate the efficiency and capability of flexible application because of no LED array aligning considered.

The resolution of wavelength scanning of diode laser can influence the performance of interferometer mostly. In this article, we propose a method to improve the precision of wavelength calibration by using the theory of energy centrobaric correction for discrete spectrum. An optical wedge whose angle of tilt was known has been set in the optical system to measure the series of wavelength on time using a 2D Fourier Transfer (FT) of the interferograms generated by both surfaces of optical wedge. An energy centrobaric correction method is also put forward to evaluate the distribution of frequency and phase of fringe pattern generated by front and rear surface of optical wedge. The results of simulation and experiment show that the error of wavelength calibration reach to 0.01pm by correlating the distribution of frequency and phase of interferograms. The benefit is that the precision of wavelength of diode laser is improved significantly with a higher signal-to-noise ratio. This method can used to any tunable diode laser wavelength to improve the precision of measurement due to its simplicity and practicability.

In-situ measurement is an ideal method to improve the precision and efficiency of manufacturing. This paper developed an in-situ subaperture stitching interferometric measuring system for large plano optics in the workshop environment. It can realize high precision and considerable repeatability. The principle of in-situ subaperture stitching measurement was introduced briefly. A validation test has been presented to verify that the in-situ measuring can be realized with the developed system.

Quantitative phase imaging (QPI) plays a key role in many application areas such as Optical elements measuring and unstained biomedical live samples imaging. Therefore, several computational QPI methods have been developed and widely used, like transport-of-intensity equation (TIE) based techniques and differential phase contrast (DPC) based techniques. However, these phase retrieval approaches are fundamentally limited by the space-bandwidth product (SBP) of the optical microscopy system, resulting in a trade-off between the spatial resolution and field of view (FOV). Lately, this problem is effectively solved by a new computational imaging technique named Fourier ptychographic microscopy (FPM), which reconstructs high-resolution complex image from many angle-variable illuminated, low-resolution intensity images captured by a low numerical-aperture (NA) objective. Although FPM has great potential for finding application in digital pathology and cancer research, it still suffers from long acquisition time and low phase measuring accuracy. Due to the large number of low-resolution images (generally larger than 30 images) required in FPM for recovering one phase image, it is more difficult for FPM to realize real-time phase imaging comparing with TIE (at least 2-3 images) or DPC (at least 4 images). Herein, we report a real-time FPM technique based on annular illuminations (AIFPM) for quantitative phase imaging of unstained live samples in vitro. In AIFPM, we only need four low-resolution images, corresponding to four different illumination angles with 0.4NA, which equal to the NA_obj. Therefore, using a 10X, 0.4NA objective lens with final effective imaging performance of 0.8 NA, we present the real-time imaging results of in vitro Hela cells mitosis and apoptosis at a frame rate of 25 Hz with a full-pitch resolution of 655 nm at a wavelength of 525 nm across a wide FOV of 1.77 mm² . Our work reveals an essential capability of FPM towards highspeed high-throughput phase imaging applications, such as biology and medicine screening, for the significant breakthrough in both space and time.

Phase-only hologram is the way to generate holograms generated by computers. Although the imaging quality is generally acceptable, the edge and line patterns of the reconstructed images are fuzzy. In this paper, we propose two methods which are the image preprocessing of the original images based on edge-preserve to improve the imaging quality. One is to use the Smallest Univalue Segment Assimilating Nucleus (SUSAN) for the extraction of original image edge, and the other one is to employee the Gaussian filter in frequency domain to separate high frequency and low frequency. Numerical reconstructions and optical reconstructions with a phase-only spatial light modulator (SLM) show that these methods can enhance the edge and line patterns of the reconstructed images, and the merits and drawbacks of the imaging quality using two methods are analyzed.

Digital holographic microscope (DHM) as a quantitative phase imaging and surface metrological tool for microstructure objects has shown increased interest over the past two decades. In this paper, we report the development of two commercial digital holographic microscopes (reflection mode and transmission mode) for different applications. The two microscopes all use a CCD camera for recording of a digital off-axis hologram and a numerical method for reconstructing the hologram. The user-friendly software simultaneously provides an amplitude image and a quantitative phase image of the object. Furthermore, additional features include various image enhancements, cross-sectional and line profiling, measurement and data analysis tools. Some applications of the two products are presented on different specimens, such as MEMS, cells.

The terahertz Gabor inline compressive holographic tomography can obtain richer information than 2D images and has potential for practical application. Due to the current terahertz detector sensitivity is not high enough and the laser light intensity is weak, we often make some holograms added together and then averaging. At the same time, the holograms averaging can eliminate speckle noise in holography. Considering the actual target and its back-bottom material are inhomogeneous, we simulated the target and its background that containing Gaussian noise. This paper mainly studies that the holograms averaging influence the compressive sensing algorithm sparse restriction parameters on the reconstruction results under Gaussian noise conditions when iteration number is 200. Finally, we give the best reconstruction parameters. This simulation study is possible benefit to the practical application.

Digital holography is a powerful tool for non-contact quantitative phase imaging. Off-axis configuration remains a popular choice among the digital holography systems due to its ability to separate the dc and cross-terms in the recorded hologram in Fourier spectral space.However, compensating the off-axis tilt of the reference wave is one of the open challenges in the off-axis digital holography.Deng et al. proposed an off-axis tilt compensation method based on hologram rotation [DENG et.al. Opt. Let., 2017]. The off-axis tilt is removed by subtracting the phase of the digital reference hologram obtained by rotating the original specimen’s hologram from the retrieved phase corresponding to the original hologram. Nonetheless, Deng’s method is extremely time consuming due to the computation of Fourier transform,inverse Fourier transform and phase unwrapping for many times. In this paper, we propose a simple algorithm to compensate the off-axis tilt . Firstly, apply Fourier transform to the original off-axis hologram, filter out the first-order spectrum by band filter, then determine directly the spectrum of digital reference hologram from the spectrum of the original hologram, then filter out the first-order spectrum from the spectrum of digital reference hologram, apply inverse Fourier transform to the two first-order spectra to obtain two complex fields, then retrieve directly the phase difference from the two complex fields using the direct phase difference algorithm, then unwrap the wrapped phase map by the phase unwrapping algorithm. Finally, simulations and experiments are conducted to prove the validity of the proposed method. The results are analyzed and compared with those of Deng’s method, demonstrating that our method not only can speed up by more than 50% the calculation time, but also can improve measurement accuracy.

Surface and internal defects of object are one of the most important reasons causing product quality problems and failures, including micro-cracks, micro-scratches, nano-deposition particles. In order to obtain the multi-layer information of the object, this paper proposes the wavelength-scanning digital holographic method. The algorithm is simulated to analyze the feasibility of acquiring the layered information of objects and the separation effect. Compared with the micro-hologram by compressive sensor, the result shows that digital holographic tomography based on wavelength scanning has a good separation effect on multi-layer object information and defects can be detected clearly.

In the study of the morphology and dynamic physiological characteristics of living cells, label-free quantitative phase imaging has been the most ideal detection technique. In this paper, we set up a set of white-light common-path digital holographic microscope based on grating diffraction, which can acquire high-resolution quantitative phase image with a very high spatiotemporal imaging sensitivity. Living red blood cells are measured and the accurate quantitative phase images are achieved. Experimental results demonstrate that this system has a very high accurate imaging performance and has the ability to detect living cells.

We present multi-exposure compressive in-line holography (MCIH), which applies compressive holography to multi-exposure in-line holograms. Multi-exposure holograms of 4D moving object can be captured continuously at different time by in-line hologram recording setup. A new single hologram is generated by coded multi-exposure holograms uniformly. 4D moving object can be reconstructed by the new single hologram. And then the trajectory of moving object can be tracked, and the location of time-space object can be defined. The method is verified by two experiments. The results of experiments show that MCIH can obtain the time-varying location of moving object.

Transparency reconstruction has been a challenging problem in active 3D reconstruction, due to the abnormal transparency appearance of invalid depth and wrong depth captured by structured light sensor. This paper proposes a novel method to localize and reconstruct transparency in domestic environment with real-time camera tracking. Based on the Sighed Distance Function(SDF), we estimate the camera pose by minimizing residual error of multiple depth images in the voxel grid. We adopt asymmetric voting of invalid depth to curve the transparency in 3D domain. Concerning the wrong depth caused by transparency, we build a local model to investigate the depth oscillation of each voxel between frames. With the fusion of depth data, we can get the point cloud of transparency and achieve a higher-quality reconstruction of an indoor scene simultaneously. We explore a series of experiments using a hand-held sensor. The results validate that our approach can accurately localize the transparent objects and improve their 3D model, and is more robust against the interference of camera dithering and other noise.

Phase unwrapping is a vital part of optical measurement technology. The path-following method based on quality map, the mainstream technology in single fringe-pattern phase unwrapping, can suppress the error propagation of phase unwrapping effectively. However, the time consumption of this technology will increase significantly along with the increasing of pixels in a fringe pattern. For this reason, a phase unwrapping method based on region division was proposed, through bidimensional sinusoids-assisted empirical mode decomposition (BSEMD). In this method, the problematic regions where the phase unwrapping error is easy to occur such as object edge and local shadow will be divided. In these problematic regions, the quality-guided phase unwrapping method will be applied, where the instantaneous frequencies acquired in the process of extracting wrapped phase are taken as quality map. Then flood fill algorithm will be applied in the rest regions directly. Through simulation and experiment, the proposed method greatly improves the processing speed while ensuring the accuracy.

In stereo vision ranging system, the parallel binocular pinhole camera model is commonly, actually, the regular binocular stereo camera is not strictly parallel. In order to improve the accuracy of binocular stereo vision ranging system, a new non-parallel binocular model ranging system using combinations of linear and nonlinear methods is proposed. This ranging system sets up a linear stereo pinhole camera model, and determines the intrinsic and extrinsic parameters of two cameras by the classic calibration method. After rectify the images, the system adopts the nonlinear scale space theory to extract the feature of the image, it using improved KAZE algorithm for feature extracting and stereo matching. Compared with the classic SIFT and SURF algorithm, the experimental measurements show that this ranging system has high feasibility and precision. The ranging accuracy within a certain scope meets the application requirements, and according to the actual situation, this system can be adjusted to suitable for vehicle ranging and robot distance measurement.

This paper presents an approach for stereo-based 3D face reconstruction. Our approach is based on depth estimation of the face by using the stereo image pair, requiring neither expensive devices nor generic face models. In order to improve the depth estimation, our approach incorporates face properties to enhance the 3D face reconstruction. The approach starts with a sparse disparity map with 68 facial landmarks detected by dlib toolkit. Considering the face symmetry and smoothness, we complete the dense disparity estimation with the guidance of the sparse disparity map. Post-processing is implemented including outliers removal and surface mesh. Experimental results provided show that the algorithm is promising.

Phase retrieve is an important step for phase shifting profilometry (PSP). The existing phase retrieve methods can obtain the phase value successfully for static object. However, as multiple fringe patterns are required in PSP, when the object has movement, errors will be introduced. A new phase retrieve method for the object with 2D movement is proposed in this paper. The 2D movement is divided into translation movement and rotation movement. Then their influence on the phase value is analyzed and a new reconstruction model including the movement information is given. At last, the phase value is retrieved based on the new reconstruction model. The proposed method can eliminate the errors caused by 2D movement of object. The effectiveness of the proposed method is verified by simulations.

The hand-eye system calibration, aiming to achieve the relationship between the robot hand and vision sensor mounted on it, is an important technique in the robot applications, involving automatic 3D measurement, visual serving, sensor placement planning, etc. Generally, the key issue of hand-eye calibration is equivalent to solving the homogeneous transformation matrix X from the equation of the form AX=XB. In this paper, we develop an accurate hand-eye calibration method by establishing a global objective function, in which the errors of camera calibration and robot movements have been considered. It is constructed based on the minimizing the projection error from the target benchmarks to the camera retina plane at all robot motions. The experimental results prove that the proposed algorithm can accurately solve the hand-eye calibration problem. Meanwhile, we set up an automatic 3D measurement system based on a robot and a rotary table, and developed a calibration scheme for the system to achieve the multi-view and fully automatic 3D data acquisition by using a fringe projection 3D sensor.

At present, the examination of scoliosis diseases is performed by x-ray, which cannot be used frequently because of its radiological hazards. So, some patients may miss the best remedial opportunity. This paper presents an image-based spine morphology detection method for patients’ daily inspection. To embed this method in software development of a portable device, such as a mobile phone, we adopt a "single-camera, multi-perspective" system construction scheme that focuses on online camera calibration of external parameters, enabling the system to use a single camera for 3D measurements. By touching the back of the human body to find the spinous processes and marking them, we photograph the markers and a checkerboard into the same image from different directions. Based on the principle of stereo vision, we use the checkerboard information to obtain the camera external parameters, then calculate the 3D coordinates of the markers by the marker information of images. At last, the spine Cobb angle is calculated based on the 3D coordinates of the markers. In the experiment, the method was verified by using a camera to measure the 3D coordinates of the centers of a series of circle markers which drawn on a paper then pasted on the plate. The result illustrates that with our method the error of coronal and sagittal Cobb angle is within 3° which has met the measurement requirements of the doctors. It suggests that our method can be used for the portable device development for patients’ daily inspection.

In fringe projection profilometry, using multi-frequency fringe patterns allows us to determine fringe orders automatically, thus unwrapping the measured phase maps. Simultaneously, doing this provides a possibility of correcting the effects of the projector nonlinearity directly from the captured fringe patterns. This projector nonlinearity decreases the measurement accuracies by inducing errors appearing as ripple-like artifacts on the phase maps and, further, on the reconstructed 3D shape surfaces. Theoretical analysis shows that these artifacts, depending on the number of phase shifts, have multiplied frequencies higher than the fringe frequencies, and their amplitudes are dependent on the extent of the projector nonlinearity. These facts imply that, we estimate the amplitude of the artifacts from two phase maps of the fringe patterns having different frequencies, by exploiting the statistics of the differences of their phase errors. By subtracting out the artifacts from the phase maps, the effects of the projector nonlinearity on the measurement results can be suppressed significantly. Experiment results demonstrate that this proposed method offers some advantages over others, such as working without a photometric calibration, being applicable when the projector nonlinearity varies with time, and being efficient in computation.

This paper proposes a 6-DoF measurement method for industrial parts with complex shape based on monocular vision. Offline template library building, image layering preprocessing and evolutionary optimization matching are studied. Firstly, a 3D model is created using the CAD file of the target part, and a matching template library of the target model with multiple pose information under different observation directions is established offline. This method of creating a matching model based on CAD files extends the matching algorithm to space 6-DOF pose detection for complex structural parts. Then the improved Chamfer Match method is used to process the image, and the distance map is layered by the edge inclination angle, so that the established matching degree function between the image and the template has higher sensitivity and the accuracy of the measurement result is improved. Finally, the evolutionary optimal search Genetic Algorithm is used to further improve the matching efficiency. We build a monocular vision measurement system to perform 6-DOF measurement experiments of two industrial parts with different structures, and also evaluate the dynamic tracking abilities. The results show that the position measurement error of this method is within 2mm, the attitude measurement error is about 3°, and the single measurement time is within 500ms. It basically meets the requirement of real-time tracking of dynamic targets.

At present, fringe projection profilometry has also been limited with a trade-off between speed and accuracy. For achieving high accuracy measurement, phase-shifting and phase-unwarpping operations will always be used for phase correspondence, however, the phase-unwrapping processing does not contribute to improve the phase accuracy, but just to distinguish phase steps. For futher reducing the projection pattern for phase-unwarpping, we propose a novel method for phase corresponding in bi-cameras system without phase unwrapping. Phase-to-3D mapping structures are utilized to obtain the candidate correspondences and eliminate the ambiguties with wrapped phase, which is implemented efficiently without time-comsuming phase correspondence searching. The experiments on both static and dynamic scenes are perfomed to verify its capability of 120 fps 3D reconstructing speed by overlapped using 3-step phase-shifting pattern.

In the recent times, optical technology is progressing by leaps and bounds largely due to the contribution of computer science. However, such optical system configuration is often difficult even for students from computer science as well as students from other disciplines to understand. The sophisticated nature of optics poses to many students as a challenge as the majority of them may experience difficulty in setting up the optical systems and struggle to comprehend them to a greater depth. In this paper, a novel optical engineering kit developed and maintained by OPSS is proposed. We hope that students may benefit from the hands-on experience by experimenting with the Optics Kit and gain insights from the various interesting applications of optics.

Nowadays, retail products recognition technologies are mostly based on traditional two-stages computer vision methods. Those methods first create features manually, followed by a classification algorithm to distinguish all products. Since deep learning methods have achieved state-of-the-art results on many tasks and have unified pipelines, it would be promising to apply deep models into products recognition. In this paper, we have built up a new light CNN architecture named ProNet for this task. The 27-layers ProNet combines the advantages of ResNet and Mobilenet. Depth-wise separable convolution and residual connection are two main operations in the architecture design. Depth-wise separable convolution is used to cut down the computation cost. Residual connection is used to help network learn better feature representations and converge to a better point during training. Compared with other commonly used CNN architectures, our ProNet is relatively computational efficient, but it can still get good performances on several public datasets. We first test ProNet architecture on ImageNet dataset. Top 1 average accuracy of 70.8% is got. After that, we test ProNet on another public dataset ALOI and our own task-specific retail products dataset GroOpt using transfer learning. Using this base model, we get an average accuracy of 98% on ALOI and 96% on GroOpt, which are both much higher than traditional SIFT based methods. Results show that ProNet is an accurate model. To make ProNet transferable in other environments, we apply the following two strategies: (1) a white balance augmentation algorithm to randomly change the RGB ratio of every image. (2) add another linear classifier on top feature maps to help distinguish very similar samples. Using augmented training set and modified model, we have trained ProNetV2. This improved version gets an accuracy of 99% on both ALOI and GroOpt. We have also embedded ProNetV2 model into a smart phone with 2GB RAM and test it under different situations, including different light illuminations, backgrounds, etc. An average accuracy of 96% and processing time of 0.1s per image are reached. Those results prove the effectiveness and usefulness of our proposed networks.

CameraLink technology is a high-speed serial data connection standard widely applied in industrial cameras. In order to realize the displaying and processing of video based on industrial cameras with CameraLink interface, this paper has presented a video protocol conversion system based on Altera’s Cyclone Ⅲ FPGA. The system is able to convert CameraLink video outputted from the camera into High Definition Multimedia Interface (HDMI) signals for displaying. The system consists of power module, CameraLink receiver module, FPGA, as well as HDMI output module. The PCB of the system is designed with Altium Designer 16 and the software is designed on the Quartus II platform using Verilog HDL. The FPGA accomplishes CameraLink signal processing, color space conversion from RGB to YCbCr 4:2:2 and HDMI output chip configuration. The experiment results show that this system is stable enough that can reliably achieve HDMI video displaying, which is able to be applied to video displaying of industrial cameras with CameraLink interface.

In order to correct the distortion phenomenon of photoelectric image acquired by CCD camera because of bigger visual field, a correction method based on using bilinear interpolation to control rectangular grid interpolation in radial distortion model is proposed. The basic principle that corrects the image which has geometric distortion was analyzed in detailed. Firstly, the distortion correction model along the radial direction and the subsequent image processing are analyzed. After the preliminary correction, in order to correct the non integer position of the distorted image, the gray interpolation and curve fitting was given. Finally, so as to prove the correctness and validity of the basic principle analysis, a distortion correction experiment of photoelectric image acquired by CCD camera is actualized, the subjective and objective results are presented to validate the proposed method.

Solder ball detection in full-field ball grid array (BGA) images has a broad range of applications, such as height extraction of solder ball, inspection of substrate coplanarity, and defective detection. Existing methods usually have poor performance due to the diversity of defects, image noise, and the disturbances of background. In this paper, we propose a coarse-to-fine process for solder ball detection by combing the strength of the threshold method and the active contour method. In the coarse process, the solder ball is roughly segmented by a simple threshold method. In the fine process, the region information and shape prior are integrated into the energy function of the active contour method to better segment the solder ball. The initial shape used in the fine process can be given by the simple threshold method in the coarse process. Experiments on full-field BGA images demonstrate the robustness and accuracy of our method.

The traditional Canny algorithm has the problem of edge loss in the process of smoothing the image and needs to set up the high and low threshold, an improved adaptive edge detection algorithm based on Canny is proposed in this paper. Firstly, the improved anisotropic diffusion filter is used to smooth the image, and the edge is protected when de-noising. Then, 4 gradient templates in horizontal direction, vertical direction, 45° direction, and 135° direction are used to calculate gradient amplitude. Finally, the threshold is adaptively determined according to the gray histogram of image. Experimental results indicate that the proposed algorithm has better anti-noise performance while detecting more edge details.

Pipe thread plays an important role in modern industry. Traditional methods of pipe thread detection is inefficient and inexact which cannot fulfill the detection needs of modern production.Based on the actual industrial detection requirements, CCD is applied to detect outline dimension of the pipe thread and digital image processing techniques is applied to the image processing of pipe thread in this paper. According to the characteristics of the pipe thread, The filtering and edge detection algorithms in traditional image processing are optimized to realize the accurate image edge contour extraction. By calculating, the geometrical parameters of the pipe thread is obtained, the experimental results show that the improved method can improve the measurement accuracy compared with the traditional method.

In view of the difficulty of defects detection of complex metal curve surface in uneven illumination and high speed processing, a new, simple, yet robust algorithm based on statistical feature of local visual field is proposed. This algorithm first performs the ideal image difference by extracting the template from the image itself, and then computes the statistical feature in local visual field to correct the gray-scale fluctuation in each region of image. In this way, the influence of the uneven illumination at low and high frequency is eliminated concurrently, which achieves the equalization of the statistical features of the local visual fields except the position containing the defect, so as to use the global threshold in whole image reasonably; Next, on the search of defects, this paper replaces the pixel level with the local field of vision and compresses the image information with the defects’ scale which is in line with the human eye. This not only reduces the influence of random noise, but also greatly improves the processing speed while preserving defects information, which makes it possible to realize real-time processing ability for image with the large amount of data. To detect complex curved surface on semi-finished metal shell of cell phone, the experimental results demonstrate that the defects detection accuracy of the proposed algorithm can reach 95%, and the detection time for single test area is less than 1ms, which is suitable for accurate and real-time detection on the production line for such surface defect.

The electronic leakage on power facility can be positioned by detecting the spectrum on solar blind ultraviolet band, produced by corona radiation. Based on this theory, the corona detector has already been developed home and abroad. In contract with manual corona detector, using corona detector with unmanned aerial vehicles (UAV) can not only detect and track the high-voltage power lines automatically in remote areas, but also reduce the consumptions of manpower. But the way to recognize power facilities under the circumstances of high moving speed and co mplex imaging background is the main difficulty on auto corona detector. So this paper puts forward an algorithm which can recognize and focus power facility fast and precisely. This algorithm firstly realizes auto-focus by using Sobel operator as image quality evaluation function and using improved mountain search algorithm as the control law of motor, then locates the power facilities by applying Hough transfer and region grow split algorithm under the circumstance of complex imaging background. The algorithm was tested on DM6467t embedded platform, and the results shows that this algorithm can recognize target accurately, realize auto-focus rapidly and locate the electronic leakage position.

When underwater camera is used to carry out the visual inspection after fuel reloading in nuclear power plants, heat exchange between fuel assemblies and water can generate underwater turbulence effect, which causes imaging distortion, and then affects position measurement accuracy of nuclear fuel assemblies. A new online visual inspection method for fuel assemblies in nuclear power plants is proposed in this paper. The method consists of image restoration and deformation inspection. A turbulence image degradation model is established at first. In the model that water turbulence weakly satisfy a Gaussian distribution. A temporal high pass filter by image quality assessment and a mean filter in time domain are used to remove the morphing of acquired original sequence images according to the degradation model. And then a spatial Wiener deconvolution filter is used to remove the image blurring that is caused by the above mentioned mean filter. The next step is using the deformation inspection algorithm to get the fuel assembles precise position. The distance of feature holes (S-hole) is solved by calibrated underwater parametric camera model. The experimental results show that the underwater image restoration method can effectively remove the image morphing that is generated by turbulence effect. The proposed online visual inspection method has a high detection precision. And the average error of the solved feature holes’ distance is less than 0.1 mm when the execution time of the method is lower than 0.5 s.

In traditional fingerprint biometrics, fingertips stained with water, dust or fake fingerprints can lead to security issues such as false rejection and acceptance. It has been found in biology that the fingerprint pattern also exists in the papillary layer inside the fingertips, which is the source of the external epidermal fingerprint. Optical coherence tomography (OCT) is a noninvasive imaging technique that captures micrometer-resolution, three-dimensional images from within biological tissues. In this paper, a spectral domain OCT system is established to measure subcutaneous information from fingertips with large area and high resolution. A hybrid hierarchical clustering is proposed to identify the contours of the corneum stratum and papillary junction, with which the internal and external fingerprints can be extracted, respectively. The experimental results show that the external and internal fingerprints obtained by OCT have same pattern and almost same minutiae distribution. Thus the internal fingerprint can be a good replacement or complement of the external fingerprint, and the detection of internal fingerprint can defense against fake fingerprints.

In this Letter, we present a new active micro-scanning setup and associated super-resolution (SR) phase reconstruction method in lensfree microscopy to achieve SR dynamic phase imaging. By rotating two orthogonal parallel plates to achieve controllable micro-scanning, a set of low-resolution (LR) intensity images with relative sub-pixel displacements can be acquired. These LR intensity images are then processed sequentially based on the matched imaging pixel transfer model and SR reconstruction algorithm to obtain the super-resolved quantitative phase images. The reconstructed result of Benchmark Quantitative Phase Microscopy Target (QPTTM) demonstrates the resolution enhancement quantitatively, which achieves a half-pitch lateral resolution of 775 nm over a large field-of-view (FOV) of ∼ 29.84mm² , surpassing 2.15 times of the theoretical NyquistShannon sampling resolution limit imposed by the pixel-size of the sensor (1.67 μm). Investigations of unstained Hela cells are then presented, suggesting that the method developed can provide promising application in the dynamic study as well as morphological analysis of the subcellular features for unlabelled biological samples.

Visual inspection is a common procedure during outages of nuclear power plants. For the underwater visual inspection of the nuclear plant reactor after fuel reloading, the water turbulence generated by nuclear fuel assemblies can seriously degrade the quality of video. Online image restoration is required in order to meet the need of minimizing the duration of visual inspection. The paper proposes a new method to solve the image degradation and to realize online image restoration when visual inspection. First, the image degradation model is founded. In the model that water turbulence weakly satisfies a Laplacian distribution, it is demonstrated in the paper that the geometric distortion can be removed and a corrected image can be recovered. Then the image is partitioned into small patches which have partly overlapping between adjacent areas. Image quality assessment is used to make phases of image patches homomorphism. Image quality index method is used to image quality measurement in practice. Moreover, the phase average patches combine into a new image. At last the wiener filter is used to estimate the image which would have been observed without turbulence. The experimental result shows that the method can well realize restoration of images affected by turbulence and obtain a satisfactory effect, which can help the operator to carry out the visual inspection which underwater camera is used to achieve more accurate operation information of the fuel reloading.

Anomaly detection is helpful in many applications such as food monitoring, production testing, security surveillance, military countermeasure and so on. Spectral imaging technique is often resorted to for accurate abnormal target discrimination due to its high-resolution spectral/spatial information acquisition ability and a great number of data processing methods. Anomaly detection methods for hyperspectral imagery are contrastively studied in this paper. A self-developed visual-band hyperspectral imaging spectrometer is adopted to collect data cubes of certain experimental scene before two kinds of spectral-domain descriptors are used to execute abnormal camouflage detection. Detection effect of information divergence and generalized angle that are utilized as detection descriptors is visually and quantitatively compared and time consumption is assessed. The study is proved to be of significance to meet the anomaly detection demand that is based on spectral signature comparison and can be developed for further detection descriptor study and other imaging techniques beyond spectral imaging.

Multi-camera multi-object tracking problem shares the difficulties of both multi-camera information fusion and multiobject data association across time. Top view enjoys nice properties for object detection and tracking, such as information completeness and no occlusion. This paper utilizes the properties to address this problem by transferring object representation to a ‘top view’ from multiple partial views, hence converts multi-camera tracking problem into a singlecamera one. To this end, a detector was applied on each single partial view image firstly. After that, to obtain the representation of these detection resultsin a common top view, we first introduce the ‘real top view supervised transferring’ method, in which, a network was used to transfer the detection-bounding box in partial view to real top view. However, this method depends on top view image as supervision signal during training. We investigate further to eliminate the dependency, so here came the virtual top view, which is in essence a hyperspace. A convolutional network and triplet loss were used to map an object with its position in each partial view to a vector in the hyperspace and supervises the learning of representation respectively. Finally, by applying cluster algorithm on the transferred representation of object in the top view, the information from multiple partial cameras was fused and unified. Tracking on the top view can be formulated as a data association problem, which can be solved by traditional assignment algorithms. Experiment results on our own dataset and EPFL dataset[1] showed the effectiveness of the proposed methods.

Focus window selection is a very important step in the process of Auto-Focusing(AF). This paper proposes a new method for the selection of focus window, where a fast AF window selection algorithm based on image saliency region extraction is used to cut down the computation time and overcome the disturbance of the background in the automatic focusing system. Firstly, the salient object detection method based on the Minimum Barrier Plus(MB+) Transform algorithm is utilized to calculate the salient regions of the image in order to obtain a feature map. Secondly, a threshold method is used to de-noise the feature map. Then, correlation treatment method and boundary expansion method are used to build the focus window, of which the size and position are self-adaptive with the target. To the end, in this study, a comparison is made between the commonly used algorithm and the introduced window selection algorithm based on the improved MB + saliency detection in terms of accuracy and computation time. The result obtained indicates that our algorithm has better performance in highlighting the potential focus targets. And its better accuracy and less computation time make it suitable for tasks in general scenes and complex backgrounds.

In the field of optical measurement,the spherical aberration always causes a circular speckle which is symmetrical to the optic axis on interferograms and it can even blur the images.In this paper, a deep learning algorithm is put forward to identify the spherical aberration coefficients of monochromatic spherical aberration interferograms.The deep learning algorithm needs sufficient training samples, but it also takes a lot of time to collect the real interferograms as the training samples.The method of zernike polynomial fitting wave surface is much better relative to the least square method.Therefore,this paper adopts the zernike polynomials fitting method,by means of changing aberration coefficients,to obtain a large number of training samples of spherical aberration interferograms by computer simulation.Different from other traditional methods, using deep learning algorithms to identify the information of the interferograms is more efficient, the spherical aberration coefficients of interferograms can be accurately and quickly identified.What is more,this method also simplify the manual processing.

This article researches the problem of accurately tracking a target that is moving in an environment where there are a large number of disturbing factors, using multiple cameras for a larger observation field and better positioning accuracy than that of using a single camera. This paper proposes a method based on the common features learned through multidomain networks to reduce the interference of the external environment and thus more accurately and steadily track the target. The image model proposed by Multi-domain Network has significantly improved the fusion and utilization efficiency of multi-scale features. We also establish a consistent calibration of the same target between cameras by making full use of the overlapping visual field of multiple cameras and counting the number of similar pairs between the template and the target image search window to achieve target association and handover between cameras, making the cameras’ vision field expanded. By extracting the geometric constraint relationship between the cameras and combining the views of the target from multiple angles, the spatial positioning of the target object is finally achieved. Experiments show that the proposed tracking and positioning method can accurately track the moving target and can accurately position it.

Iris recognition technology has advantages of high security and high stability and can realize non-contact and living recognition. For iris recognition, iris localization is the first step. The localization precision is assurance of high recognition rate. The existing iris localization method has shortage of slow speed. In this paper, an improved iris region localization method is proposed. Firstly, the images are preprocessed with Gaussian blur algorithm. Then the center of the pupil is coarsely located by Gaussian template convolution operation. Finally, the center and the outer edge of the iris are precisely located based on the Integral-differential operation. In experiments, CASIA iris database is used to test the improved iris region localization method. The results show that the location time can be less than 200 ms and the location precision can reach 98. 82%. This method’s usefulness is verified and can promote the application of the iris recognition

This paper presents an image segmentation method for stacked objects using Region-Scalable Fitting (RSF) and Spatial Kernel Fuzzy-C-Means (SKFCM) based on depth images. Firstly, RSF is used to detect contours of the objects’ area. Then, it can be judged whether there are stacked objects in each contour area by image histogram . For stacked objects, SKFCM algorithm is utilized for segmenting the stacked objects. Unlike the method based on RGB images, the proposed method is insensitive to background, texture and illumination due to the property of depth images that only contains depth information. Besides, the proposed method can effectively segment each object in the case of objects stacked, and determine the order of stacking which can be used for picking up by manipulator arm. The proposed method has been tested on different scenes with objects stacked. Experimental results have shown the effectiveness of the proposed method in segmenting stacked objects.

In single-pixel imaging (SPI), the target object is illuminated with varying patterns sequentially and an intensity sequence is recorded by a single-pixel detector without spatial resolution. A high quality object image can only be computationally reconstructed after a large number of illuminations, with disadvantages of long imaging time and high cost. Conventionally, object classification is performed after a reconstructed object image with good fidelity is available. In this paper, we propose to classify the target object with a small number of illuminations in a fast manner for Fourier SPI. A naive Bayes classifier is employed to classify the target objects based on the single-pixel intensity sequence without any image reconstruction and each sequence element is regarded as an object feature in the classifier. Simulation results demonstrate our proposed scheme can classify the number digit object images with high accuracy (e.g. 80% accuracy using only 13 illuminations, at a sampling ratio of 0.3%).

In fringe projection profilometry, three-dimensional reconstruction result with higher spatial resolution could provide more detailed description of the measured object. To increase the spatial resolution of three-dimensional reconstruction result, this paper proposes a method to improve the resolution of the absolute phase map recovered in fringe projection profilometry with the digital images of different resolutions. In this method, the same fringe patterns are sampled with the images of different resolutions, the absolute phase maps of different resolutions are obtained respectively. Since the sampling points of the digital images under different resolutions are not coincident, additional ground truth depth information of the object surface is obtained. To emerge an absolute phase map with higher resolution, an algorithm is developed to fuse the absolute maps in different spatial resolutions together. The proposed method can be used to obtain a three-dimensional reconstruction result with higher spatial resolution for various applications. The effectiveness of our proposed method is validated by simulation results.

Phase-shifting profilometry (PSP) is a widely used approach to high-accuracy three-dimensional shape measurements. However, when it comes to moving objects, phase errors induced by the movement often result in severe artifacts even though a high-speed camera is in use. From our observations, there are three kinds of motion artifacts: motion ripples, motion-induced phase unwrapping errors, and motion outliers. We present a novel motion-compensated PSP to remove the artifacts for dynamic measurements of rigid objects. The phase error of motion ripples is analyzed for the phaseshifting algorithm and is compensated using the statistical nature of the fringes. The phase unwrapping errors are corrected exploiting adjacent reliable pixels, and the outliers are removed by comparing the original phase map with a smoothed phase map. Compared with the three-step PSP, our method can improve the accuracy significantly for objects in motion

In this work, we demonstrate that by using a quad-camera multi-view fringe projection system and carefully arranging the relative spatial positions between the cameras and the projector, it becomes possible to completely eliminate the phase ambiguities in conventional three-step PSP patterns with high-fringe-density without projecting any additional patterns or embedding any auxiliary signals. Benefit from the position-optimized quadcamera system, stereo phase unwrapping can be efficiently and reliably performed by flexible phase consistency checks. Besides, redundant information of multiple phase consistency checks is fully used through a weighted phase difference scheme to further enhance the reliability of phase unwrapping. This paper explains the 3D measurement principle and the basic design of quad-camera system, and finally demonstrates that the resultant dynamic 3D sensing system can realize real-time 3D reconstruction with a depth precision of 50 μm.

In order to avoid frequency aliasing,improve the spatial resolution of the phase map in Fourier transform Profilometry(FTP),an approach based on the digital time-multiplexing technique is proposed to remove the background component from the deformed fringe pattern. Firstly, a sinusoidal fringe pattern is projected onto the tested object by digital-light-processing( DLP) projector, the fringe pattern modulated by the object’s surface is captured by a CCD camera.Secondly, apply Fourier transform to the captured fringe pattern to obtain the spectrum. Thirdly, rotate the specimen’s fringe pattern 90-deg to obtain the rotated fringe pattern , then obtain the new spectrum corresponding to the rotated fringe pattern.Fourthly,the new spectrum is subtracted from the original spectrum ,clip the negative going values in the resultant spectrum by digital manipulation.Fifthly, filter out the first-order spectrum from the resultant spectrum by the band filter,apply inverse Fourier transform to the selected spectrum to obtain complex fields,then retrieve the phase, unwrap the wrapped phase map by the phase unwrapping algorithm.Finally, the simulation and experimental evaluations are conducted to prove the validity and performance of the proposed method. The results are analyzed and compared with those of the conventional method.The effectiveness and superiority of the proposed method have been demonstrated and verified.

In recent years, fringe projection profilometry (FPP), as a kind of three-dimensional shape measurement technology, has achieved the great breakthrough, due to the rapid development of the high-speed camera and high-speed projection equipment. The number-theoretical approach, as a classical method for the temporal phase unwrapping algorithm, is suitable for the binary defocusing FPP since it can avoid the acquiring of low frequency fringes. However, in order to ensure the stability of phase unwrapping, the period of fringe is generally around 20, which leads to the limited accuracy of 3D measurement. In this paper, we propose a bi-frequency number-theoretical phase unwrapping method with depth constraint. Using the principle of depth constraint, we will eliminate the period ambiguities of each pixel within a pixel-variant local period range so that the method only requires the coprime of two fringe frequencies within the local period range instead of the conventional global range. In this way, the requirement of stability of the traditional number-theoretical phase unwrapping can be adjusted from global range to local range. The stability is higher in the local period range due to containing less period ambiguities. As a result, we can realize phase unwrapping of higher frequency fringes with the same stability. Several experiments on various scenes are performed, verifying that our method can achieve high-speed and high-precision 3D measurement.

Binocular stereo vision, as a typical technique of computer vision, is versatile in three-dimensional shape measurement. However, the efficiency and speed are limited by the inherent instruction cycle delay within traditional computers, leading to large quantities of image data and computational complexity. Consequently, this paper describes a real-time binocular stereo vision system based on FPGA implementation. Considering FPGA’s parallel architecture, both in storing and calculating, the whole system is a full-pipeline design and synchronized with the identical system clock so that different parts of the stereo processing can work simultaneously to improve the processing speed. As the complete image processing framework contains rectification, stereo correspondence and the left-right consistency check is realized by only one FPGA chip without other external devices, making system highly integrated and low cost. To avoid unnecessary cost of the FPGA resource, the dual-camera calibration is done offline by MFC-based software while the intrinsic and extrinsic parameters are transmitted into the FPGA through system interaction.

Tabletop 3D display is a device that can provide several position-dependent 3D scenes in a circular viewing zone to viewers. In this paper, a kind of new method could provide a tabletop 3D display which was designed with the pixelated nano-gratings in pixels of the image and fabricated to modulate the collimated illumination light and project multiple converged transmitted light beams into each circular viewing zone. In this monochromatic tabletop display prototype, several viewing points were achieved in a circular viewing zone. The minimum angular separation set in this prototype between adjacent viewing points was 1 degree and the angular divergence of each viewing angle was measured and calculate as 0.958 degree. In this paper, the resolution of the generated 3D image at each view was 640×360 pixels. Using the proposed technology, the 360-degree viewable 3D display system can be constructed easily with multiple viewing points either evenly or unevenly distributed in the viewing zone. In addition, several artificially generated 3D image can be mixed well with the real physical objects placed on the tabletop screen, suggesting a natural mixed-reality environment provided by the proposed system. The potential applications of the proposed tabletop 3D display system are very comprehensive including desktop conference, tables games, trade show display, and sandtable.

Laser self-mixing interferometer is a novel remote sensor which permits measuring micro vibration displacement of scattering targets, making it apply to noncontact detection of landmine buried in the ground. An experimental model is developed for acoustic/seismic landmine detection using a laser self-mixing interferometer to obtain the velocity variations image of the ground excited by acoustic wave. Interferometer has a noise floor due to speckle noise, thus sound pressure level should strong enough to stimulate landmine to vibrate in a mode higher than interferometer noise floor. Vibration response in frequency domain and 2D image are obtained with laser self-mixing interferometer in the field test, and results demonstrate it is feasible to detect landmine and distinguish landmine types from the shape and size of the image.

Cultural Heritage (CH) is concerned with objects and materials that witness the historical evolution and human civilisation and are due to be inherited to next generations. As such prevention of damage and failure is an ultimate never-ending aim in art conservation science if CH protection is concerned . Interferometry techniques offer the spatial sensitivity to assess minor changes prior to damage while important ethic principles of non destructivity, non contact and non invasive type of measurements are satisfied as basic requirements for art object examination. Visual qualitative evaluation of the state of condition as provided by interference patterns as well as the quantitative surface morphology of deformation are important information sources for the conservation documentation acting as tools in the hands of the conservator. Hence it is herein briefly described how our optical laboratory explore the trends in modern interferometric instrumentation to adjust it to the needs for documentation in Cultural heritage field. In this context the development of a portable interferometry system based on the fundamentals of holographic and speckle interferometry satisfying the limitations and over passing the state of the art in on-field measurements for structural diagnosis in CH is presented and some examples from movable and immovable artwork examination is given.

Latent fingerprint is one of the important evidences used to identify criminals in criminal cases, so fast and non-destructive detection of latent fingerprints is important. At present, the usual method always preprocess the sample before detecting the latent fingerprints, and it will cause a certain degree of damage to the latent fingerprints. Based on the characteristic that the organic components of latent fingerprints will produce the fluorescence when induced by ultraviolet, a fast, non-destructive and high-contrast detection technique is studied. In this paper, an ultraviolet induced fluorescence detection method based on two-dimensional laser scanning system is proposed to realize the rapid scanning of latent fingerprint area. The experimental parameters are optimized according to the contrast of fingerprint striae, the fingerprint image is reconstructed by image processing. In order to verify the feasibility of this method in practical application, the experiment of detecting the aged latent fingerprints on five kinds of papers deposed for different days is carried out. The detection results show that the aged latent fingerprints deposed for three days can be clearly visualized. For aged latent fingerprints deposed for five days and seven days, the contrast of fingerprint striae is reduced, but the fingerprints can still be distinguished. The method can realize fast, non-destructive and high-contrast detection of latent fingerprints on papers. It can be used in different fields such as criminal investigation and trace detection.

Electro-discharge machining (EDM) and pulsed laser drilling/trepanning are commonly used for fabricating cooling holes. Although the EDM technique produces high quality holes, it is very slow, without mentioning the high tooling cost. The millisecond pulsed laser drilling/trepanning is much faster. However, a laser with millisecond pulses usually cannot drill/trepan high quality microholes, mainly resulting from the normally encountered recast layer formation with metallurgical/morphological defects. In this study, a water-based magnetic-assisted ultrasonic-enhanced laser drilling/trepanning technique is accordingly reported for drilling and trepanning microholes with and without ultrasonic/magnetic assistance, improving laser drilling and trepanning performance. This novel technique was primarily explored through experimental characterization and numerical analysis, including the ultrasonic-enhanced laser trepanning of nickel super-alloy sheets, magnetic-assisted ultrasonic-enhanced percussion laser drilling of nickel superalloy sheets, and numerical analysis for ultrasonic-enhanced laser trepanning of stainless steel sheets. Effects of ultrasonic/magnetic assistance on millisecond pulsed Nd:YAG laser drilling/trepanning performance and quality are reported through comparing the drilled/trepanned holes without and using ultrasonic/magnetic assistance. Numerical analysis was also carried out for simulating the fields of temperature and residual stress resulting from laser drilling/trepanning with and without ultrasonic assistance.

A distortion-free telecentric camera dose not have an optical center because of the orthogonal projection. However, the position of optical center should be known when the lens distortion is considered. Since the full-scale parameters are derived through an iterative algorithm, critical initial values of the optical center should be provided to avoid being trapped in local minima. In this paper, we proposed a two-step algorithm to estimate the optical center as the trustworthy initial value for the subsequent iteration process. The first step is directly calculating the pixel coordinates of the lateral distortion center using the extracted control points. The second step is optimizing both lateral and tangential coefficients considering the properties of the affine transformation in the imaging process. The effectiveness of our proposed method is proven by the measurement results using a new developed microscopic telecentric stereovision system.

Free-form optics has been attracted huge interest since it can significantly improve the performance of an optical system with a simpler structure. However, optical testing for free-form surfaces is usually more difficult compared with traditional ones. Although a variety of interferometers can achieve measurements with nanometer-scale precision, it suffers from the problems of a complex system configuration, a limited measurement range and relatively high requirements of testing conditions, etc. In contrast, phase measuring deflectometry (PMD) which has the benefits of a simple system structure, a large dynamic range and a high measurement accuracy is gradually becoming a powerful tool for free-form surface testing. Nevertheless, multiple groups of fringe patterns are required to sequentially display in two orthogonal directions to obtain the corresponding surface gradients in the classical PMD measurement. Therefore, a speedy detection of free-form surfaces is generally blocked. To overcome the above shortcoming, a spatial color-encoded phase-shifting strategy is put forward for PMD to acquire absolute phases with only four color images in this paper. Experimental results demonstrate the effectiveness of the proposed method as well.

Surface defect detection is one of the essential steps of quality control. However, it is hard to illuminate defects on curved surface, as the surface properties and geometrical shapes lead to uneven background light distribution on the captured image. In this paper, all the devices used by machine vision including the sample are regarded as part of the whole illuminating scene. Models for each component of the illuminating scene are established separately and Monte Carlo ray tracing is used for generating the image. At last, a specific illuminating scene is designed for illuminating a part of curved cylinder surface. the entire surface is lightened and the non-uniform image caused by background light is greatly improved. The paper analyses how the components of illuminating scene, such as light source placement, surface properties, influence the grayscale distribution on image background and provides method to design illuminating scene for real-time accurate curved surface defect detection.

The wave plate is an indispensable optical element for transforming polarization state in various optical fields. In the retarder’s applications, precise measurement of the retardance is necessary. However, there is no common and effective way to analyze resolution of the retardance measuring instrument. For ensuring the retardance measurement accuracy, an analysis method involving a wedge wave plate with a tiny angle between two planes is proposed to characterize the resolution. The retardance of the wedge wave plate varies linearly and slightly due to its linear and diminutive variation of thickness. The diminutive variation of retardance versus displacement can be measured when the instrument has enough resolution. And the instrument demonstrates higher resolution when it can measure smaller retardance variation. In the experiment, a wedge wave plate is mounted on a two dimensions stage and its one surface is normal to the detecting light of the instrument. And then the retardance is measured along one certain direction and the results are fitted linearly. The method can be used to evaluate the resolution differences of retardance measurement instruments. The gained resolution of both two instruments is superior to 0.1nm. Through several experiments, it can be demonstrated that the proposed analysis method has the advantages of easy operation, high efficiency and simple configuration.

To promote the application of sampling moiré method, in this study, the determination of the moiré spacing in sampling moiré method is studied in details. The ordinary equation for determining the sampling moiré spacing is found to be inapplicable in some cases, then a new equation is derived based on the generation mechanism of sampling moiré. It is found that the ordinary equation is a particular form of the new equation in a specific range. Besides, simulation tests demonstrate that the new equation has a wide application range.

High spatial, temporal resolution and continuous measurement of atmospheric aerosols over ocean is very important to understand their role in the atmospheric processes as well as on human health and environment. A shipborne multiwavelength lidar system for aerosol and clouds in the troposphere and lower stratosphere was developed. We then conducted twice shipborne measurements onboard the vessel XIANGYANGHONG No. 8 (X8) over the Yellow Sea of China on May and September in 2015, respectively. In this paper, the optical properties of aerosol together with 180- hour continuous measurement during the 2015 Yellow Sea Experiment (2015-YSE) are presented.

In the classic subset-based digital image correlation (DIC) technique, the displacement measurement errors due to the shape function have been a key factor. Generally, the first-order shape function is widely employed. However, in the practical experiments, the order of the deformation of the specimen is higher than the selected shape function. So the errors due to the under-matched shape functions are presented. Although the systematic errors due to under-matched displacement mapping functions and the random errors due to matched or overmatched displacement mapping function have been examined, the root-mean-square errors (RMSE) due to under-matched shape function are still not investigated. In the paper, the root-mean-square errors of the measured displacements due to under-matched shape function are studied experimentally by using simulated speckle patterns.

Here a refractometer with broad refractive index measurement range is proposed. This refractometer uses the measured liquid as a liquid prism and utilizes CCD and a set of computer software based on Borland C++ to measure the refractive index of liquid. The proposed refractometer has a small volume. Meanwhile the structure and working principle of the proposed refractometer are introduced. Now the mainly used refractometer is Abbe refractometer which has a refractive index measurement range of 1.30-170. While the theoretical results of our work indicate the measurement range can be up to 1.00-3.60 when the vertex angle of the liquid prism is 30°, and the experimental results have proved it is viable.

Currently the percutaneous coronary intervention (PCI) is one of the most effective treatments for angiocardiopathy, as the main instrument of which, vascular stent’s design and processing method by laser have attracted widespread attentions. The development history of vascular stent is briefly introduced firstly. Then the structural design of vascular stent and its influence on performance, laser processing method of vascular stent are elaborated at home and abroad simultaneously. Finally, both the structural design and technological development of vascular stent are prospected in the future.

The AFM study of a series of novel nano-structure on in-situ laser irradiating GaAs(001) substrate in molecular beam epitaxy was presented. Nano-hole, nano-island and nano-ring(Chinese ancient copper coin shape) were observed after laser irradiating. The desorption of Gallium on GaAs surface varies according to different power energy and pulse numbers, leading to the formation of nano-holes, nano-islands and nano-rings. It is speculated that these nanostructures are galliumrich through the change of the RHEED stripe. What’s more, the desorption of defectless GaAs sub-monolayer was discovered, and matched dynamic evolution model (self-drilling effect dominated by Ga atom) was presented. The dependence of the temperature on the surface of the substrate with time was studied after laser irradiating according to the heat conduction equation. The drastic temperature changes caused non-thermodynamic equilibrium process which makes these morphologies.

In this work, surface modification of InAs wetting layer was carried out during InAs/GaAs (001) quantum dot molecular beam epitaxy growth by in-situ pulsed laser (355 nm/ 10 ns). We investigated the morphology transformation of wetting layer by atomic force microscope. Atomic layer removal and formation of nano holes were observed on the sample surface. It is proposed that the material removal of wetting layer induced by electronic excitation is triggered by In atom vacancies due to the desorption at substrate temperature of 480°C. The effects of surface modification on QD growth were studied by subsequent InAs deposition after laser irradiation. Preferential nucleation in nano holes were found in the experiments. This study provides a novel technique leading to site-controlled to InAs/GaAs (001) QDs fabrication.

Hyperspectral imaging spectrometer is an important measurement and analysis instrument, which combines imaging with spectrum technology. Nowadays, it has been widely used in research fields of atmosphere, ocean, geology, ecology, astronomy and so on. Convex blazed grating is a key component in the hyperspectral imaging spectrometer. At present, holographic-ion beam etching is an important method to fabricate convex blazed gratings. The common way of holographic-ion beam etching is that to etch the photoresist grating mask directly. However it is difficult to control the groove of photoresist mask accurately. This paper proposes a method of fabricating convex blazed grating by native substrate grating mask, ion beam etching and reactive ion beam etching are used to fabricate a native substrate grating mask based on photoresist grating. The diffraction efficiency of the convex blazed grating is investigated by FDTD (Finite Difference Time Domain) theory. The first-order diffraction efficiency can be over 45% within visible to near-infrared waveband through controlling the blaze angle from 6.4° to 7.2°. Furthermore, a convex blazed grating has been fabricated with the period of 2.45um, the blaze angle of 6.8° and the anti-blaze angle of 60°, theoretical analysis shows that the first-order diffraction efficiency is more than 50% within visible to near-infrared waveband.

To ensure the good performance of hyper-numerical-aperture (NA) freeform surfaces lithography objective, not only the aberration should be decreased as much as possible in theory design stage, but also all the tolerances should be allocated reasonably and controlled rigorously in the manufacturing process. Therefore, reasonable tolerance analysis for projection objective is needed to maximally make up for the image quality deterioration caused by manufacture and assembly errors. According to the variation sensitivity between Zernike aberration and the single tolerance, effective compensators for individual aberrations can be chosen during tolerance analysis. As an example the method is applied to the tolerance analysis for an NA1.2 catadioptric projection objective with freeform surfaces designed by us. The results show that, after tolerance analysis using the compensators selected by this method, the root mean square (RMS) wavefront error of the projection objective is less than 0.015λ (λ=193 nm) at 90% probability, which meets the image quality requirement of lithographic projection objective for 10 nm technology node.

In view of the ultra-precision machining for large aperture optics developing rapidly but lacking effective rapid polishing methods, the research problems worth further studying are pointed out. The current situation, removing mechanism and processing difficulties of large aperture ultra-precision machine are introduced. The quantity and diameter of plane optics are increasing year by year, but currently the rapid removing of ultra-precision machine based on deterministic control of surface shape of the meter size optical components is still a blank. The development of related field is seriously affected huge losses caused by the low precision and low processing efficiency. The research situation of the high accuracy and rapid polishing methods are introduced for the main factors in the polishing processing system, such as movement patterns, polishing pad, polishing slurry and process parameters. According to the characteristics of the polishing machining process that bad deterministic control of the surface shape and the low removal efficiency, the research emphasis should be the methods that deterministic control and rapid removing of the machine, a new generation of high precision and high efficiency rapid polishing equipment and application process suitable for the large aperture and flat optical components.

We design an effective microsystem by integrating ultra thin Ag film patterned with two-dimensional nanodisk array with a microfluidic channel. The refractive index of liquid, which flowing through the channel, is determined by measuring the transmission spectra of this integrated microfluidic device. We systematically simulated the influence of structure parameters to refractive index sensitivity. By adjusting the structure parameters of two-dimensional nanodisk array, such as period, thickness and duty cycle, the sensitivity of refractive index can be improved. The results indicated that the refractive index sensitivity can reach up to 308 nm / refractive index unit (RIU) with proper design. By this way, we can achieve intuitive, convenient and non-polluted refractive index measurement.

Scanning slit is an important element to form illumination area and control exposure dose in step-and-scan lithographic system. If the penumbra of blade’s edge generated by scanning slit is too large, the exposure performance can be affected. Moreover, the distortion in the corner of illumination field also has great impact on the integral uniformity of illumination. Firstly, the generation principle of penumbra of blade’s edge at reticle plane was introduced according to the illumination principle of the step-and-scan lithographic system, and then the calculation expression of penumbra of blade’s edge at reticle plane was derived by analyzing the relationship between the intensity distribution of light and the location and the thickness of blades along the optical axis. Secondly, according to different types of blades, the distortion at the junction of adjacent blades of coplanar scanning slit was analyzed. At last, based on the optical model of step-and-scan lithographic system with the numerical aperture of NA0.75, the illumination fields at reticle plane generated by the four blades in scanning slit were simulated. The results indicate that the penumbra of blade’s edge generated by coplanar scanning slit could be significantly reduced and the distortion in the corner of illumination field could also be improved by optimizing the structure design of the blades of coplanar scanning slit properly.

In recent years, optical fiber communication system has made a great development, but the quality of the optical signal will be seriously deteriorated by some factors, such as amplified spontaneous emission (ASE) noise, group velocity dispersion and so on. The traditional regeneration technology is accomplished within the electrical domain, and the opticalelectrical-optical conversion consumes vast amounts of energy. So it is necessary for all optical regeneration technology. This paper introduces the principle of an all-optical 2R regenerator based on self-phase modulation(SPM) and offset filtering technology. The deteriorated optical signal at 40 Gbit/s has been regenerated by the combination of SPM in highly nonlinear fiber (HNLF) and offset filtering. The factors influencing the regeneration have been analyzed by changing related parameters. It is concluded that by reasonably choosing parameters, we can get the best result of all-optical 2R regeneration.

The uniformity of the illumination field in the scanning direction is an important factor that affects the lithographic overlay accuracy as well as Critical dimension uniformity (CDU). With the improvement of lithography resolution illumination integrated uniformity is also increasing. To improving illumination integrated uniformity, a highly intelligent uniformity correction is introduced, which is used to correct the illumination integrated uniformity by inserting a plurality of independent movable correction plate arrays into the illumination field. In addition, a correction algorithm based on step by step is proposed. The simulation results show that the corrected illumination integrated uniformity is better than 0.3%, which is meeting the requirements of illumination integrated uniformity for 65nm node lithography.

A novel phase erasure and format conversion of phase-shift keying (PSK) to conventional on-off keying (OOK) is proposed and demonstrated theoretically and experimentally. Using a single-pump nondegenerate phase sensitive amplification process in a highly nonlinear fiber, the 0 and 1-bits of the PSK signal obtain different gains through amplification and de-amplification. As a result, the modulation information is transferred onto the amplitude. With an optimized input power difference between the signal and idler, the signal phase information is erased with wavelength preservation after the PSA. The output constellation and eyediagrams show an effective phase erasure and format conversion of PSK to conventional OOK. The error vector magnitude is utilized to evaluate the scheme performance. The proposed scheme provides the flexibility for future optical communication networks.

We design a broadband absorber formed by placing the cross-shaped metallic resonators, whose vertical and horizontal arms have difference length, with 90° rotated within a super-unit-cell arranged in mirror symmetry. Simulation results indicate that absorption efficiency greater than 95% can be achieved in a broadband frequency region under normal incidence. We employ a design scheme with the integration of graphene and VO₂ thin film, which allows independent electric tuning and thermal tuning. Our results reveal that the resonance will be blue-shifted with the increase of Fermi level and red-shifted with the increase of temperature. it thus broadens the tuning range of metamaterial absorbers by combining the electric tuning of graphene with the thermal tuning of VO₂ thin film. this structure may have great application potential in frequency selective detectors and testing technology

It sometimes appears resonance phenomenon that both the reflective wave and refractive wave coexist when the incident angle is a value of the range for wave through the interface for example both air and water. We design a kind of calculation method of resonance wave reflectivity on the basis of the degree of the ratio of both the normal component of incident wave the wavelength that is compressed and refractive wavelength when incident wave the through the interface. The methods could calculate resonance phenomenon that the wave travel to split into two ray direction on the interface both sides. The methods will be widely used in various fields for resonance wave calculation such as light, electromagnetic waves, sound waves and water waves etc.

Point diffraction interferometer (PDI) uses the nearly ideal spherical wave front diffracted by the pinhole as the reference, thus its measurement accuracy depends mainly on the quality of the diffraction wave front. However, aberrations and numerical aperture (NA) of the microscope objective (micro-objective) used to illuminate the pinhole in PDI can affect the quality of the diffraction wave front and further reduce the measurement accuracy of PDI. It’s necessary to analyze the influence of the micro-objective on the quality of the diffraction wave front detailly. In this paper, numerical simulation of the propagation of the incident light through the pinhole is carried out with the method of the finite difference time domain (FDTD), vector diffraction integral and vector diffraction theory. Then energy transmittance, homogeneity and deformation are obtained, which are used to evaluate the influence of the micro-objective on the quality of the diffraction wave front. These simulation results will provide a reference for rational selection of the micro-objective parameters, contributing to establish PDI system with best measurement accuracy.

In order to improve the heat dissipation of LED, Snell's law and principle of energy conservation are adopted. By applying the equal relationship between the light vectors, a mathematical model of the collimation free-form TIR lens is established. In order to reduce the heat dissipation, the TIR transmission surface is studied. Niel surface design. In order to improve the illuminance of the target, a 9×9 array design was performed on the designed Fresnel lens using Sparrow's rule. Optical simulation using lightools. When the light source array is 10m away from the target surface. The uniformity of light on the target surface not only satisfies 0.7, but the heat dissipation effect has also been significantly improved.

In recent years, with the increasing demand of intelligent transportation system for large-scale field monitoring, it is a pretty much necessity for the continuous zoom system with large scale ratio and large field angle. Therefore, based on the characteristic of its optical system with 30 times variable ratio and large field angle, the mechanical structure of continuous zoom lens has been designed in detail, and finally two kinds of cam mechanism are described in this paper in order to realize the zoom and focusing process. Furthermore, in order to meet the work environment requirements of video monitoring system for the zoom system, the static simulation and thermal deformation simulation of the key component zoom cam has been analyzed in this paper. The static analysis results show that the deformation of the force of the zoom cam is 0.0015 mm, which can be ignored. Thermal deformation analysis results show that the zoom cam at - 15 °C to 50 °C under the temperature load of maximum deformation is 0.007 mm, which has meet the requirements of the system of working temperature, and all of the above results have verified the rationality of the design of zoom cam mechanism. On the basis of the selective zoom mechanism, a reasonable focusing mechanism is carried out to ensure the focus stability of the focusing mechanism, which can provide the stability of the whole continuous zoom lens system.

High-spectral-resolution lidar plays an important role in the measurement of aerosol distributions and variations for understanding the influence on the local environment. The multi-mode high-spectral-resolution lidar is a new type of high-spectral-resolution lidar for fine detection of aerosol optical properties, which uses the multilongitudinal-mode pulsed laser rather than the single longitudinal mode laser. Considering the Mie-Rayleigh scattering signals excited by the multi-longitudinal-mode laser have the periodic characteristics, the tunable MachZehnder interferometer is selected as the optical discriminator in the construction of multi-mode high-spectralresolution lidar. In order to minimize the effect of divergence angle on the transmittance function, a filedcompensated Mach-Zehnder interferometer is designed, which has the complementary outputs to realize the transmission and suppression of Mie scattering signals respectively. The optimal optical path difference of the MachZehnder interferometer should be twice of the cavity length of the Nd:YAG pulsed laser. The capability of the multimode high-spectral-resolution-lidar has been verified using the standard atmospheric model, the simulation results show that the proposed system can achieve the accurate measurement of aerosol optical properties up to 10km.

An off-axis three-mirror detection system with a large field of view is designed in order to improve the space target detection capability. The optical system is a Cook-TMA with the focal length of 127mm, the F number of 2, the field angle of 25° × 25° and the spectral range of 400-700nm. The primary mirror and the tertiary mirror of the off-axis three mirror system are all designed by free form surfaces: the primary mirror is characterized by Zernike polynomial and the tertiary mirror is described by XY polynomial. At the same time, we analyze the related characteristics of Zernike polynomial and XY polynomial. The results show that the free form surfaces have great advantages in improving the field of view and the imaging quality of the off-axis optical system. The system has high energy concentration and good imaging quality, which can capture and track the target in a wide range is suitable for wide area target monitoring.

In high-precision vertical large-caliber flat interferometry, the gravity deformation of the reference flat will lead to a large error of the surface shape measured. Based on the analysis of the finite element method, this paper combines the three flats test method with Zernike polynomial fitting to compensate and calibrate the error of the reference flat. For the diameter of 300 mm and a thickness of 90 mm of the fused silica reference flat, the results of analysis show that the PV deformation under the T-bracing is 0.021 λ. (λ = 632.8nm). The simulation test result of the influence of deformation on the three-flats test shows that the reference flat the gravity deformation not only affects the detection of self surface, but also has a great influence on the surface detection results of the undeformed flat. And the PV of the surface shape detection results residual is close to 0.011λ. In the end, the new calibration method base on compensate reference deformation for three flats test was proposed, and the validity was verified by simulation.

We present a new method to achieve compactness for zoom lens design with a high zoom ratio. In the method, initial parameters of lens system are solved with Gaussian optics Theory. And then the first-order quantities are assigned to lens modules. After obtaining the lens module zoom system, the real lens groups are successively designed to combine to form lens system. Compared to separately designed lens groups, the approach can give a better starting zoom lens for it has only 9 variables of each group to optimize. Based on the new method, the final design is a four-group zoom system with a focal length range of 10 to 200mm. The system has a variable aperture from 1/2.8 at wide field to 1/5.6 at narrow field. The Modulation Transfer Function(MTF) exceeds 40% at 100lp/mm of all zoom positions, over all fields. Wherefore it has a good imaging performance when used with a 1/3-inch CCD.

A new channel drop filters (CDFs) configuration based on a single line-defect resonator (LDR) is presented. The proposed structure is composed of a bus waveguide, a LDR and a u-shaped output waveguide. The bandgap structure and filter characteristics of the filter are investigated by using the plane wave expansion (PWE) method and finite difference time domain (FDTD) method in a square lattice dielectric rod photonic crystal structure respectively. Though this novel resonator, the two wavelengths at 1531nm and 1551nm are dropped from the two ports of the u-shaped output waveguide with high dropping efficiency. This is very well meeting the requirement of ITU-T G.694.2 standard. The proposed CDF can play important role in optical communication networks and photonic integrated circuits.

Based on reverse recursion algorithm, the one-dimensional photonic crystal containing a Kerr nonlinear medium layer (AB)^MD(BA)^N is investigated to realize the unidirectional transmission function of all-optical diode by introducing additional dielectric layers. Results show that when a single-dielectric-layer (for example, dielectric layer A) or a doubledielectric-layer with different refractive index (for example, dielectric layer AB) is introduced in the outside of the structure, the bistable curve of the input and output light intensity for the forward and backward incident is separated, and the unidirectional transmission characteristics appear. Increasing the period of the double-dielectric-layer introduced in the structure, the unidirectional transmission wavelength range and the transmittance are both improved for the same intensity of incident light. Based on the analysis we present an optimized structure (AB)⁶ D(BA)⁸ (AB)² . Numerical simulations demonstrate that the structure exhibit ideal unidirectional transmission characteristics. Besides, the wavelength range of unidirectional transmission is also extended with the increasing of the intensity of incident light. When the intensity of incident light is 1.48MW/m² , the wavelength range of the unidirectional transmission is 1564.7nm1574nm with transmittance greater than 0.8. Compared with the results in available literatures, the proposed all-optical diode structure has the prominent characteristics of simple structure, wider wavelength range, and greatly reduced the intensity of incident light. The results are of great significance for the design of all-optical diode and other unidirectional transmission devices.

We present a optical phased array antenna with gratings by using shallow ethced grating coupler on silicon-oninsulator for large angle optical beam steering. By decreasing the spacing of antenna to 0.9 μm, The steering range of the antenna can reach as large as 106° with a SNR of -7dB. To prevent crosstalk from grating coupler with small element spacing, we change the width of each grating to cause phase mismatch between adjacent antennas. Specific design is also made to the periods of each antenna in order to make the steering angle of antenna the same. Such grating array superlattices have great potential in LIDAR and free-space communication for its large steering range and small SNR.

Zoom cam is a pivotal part used for driving every lens group in zoom lens , the design result of cam curve is decisive importance for motion property and system precision as well as system imaging in zoom system, therefore, zoom cam design is an important part of the zoom lens design, a fine cam performance is the basic requirements to reach lens design of image quality goal and optical zoom process. a new method is presented in this article, it adopts the method of piecewise processing to establish several common functions in steep interval so as to make the arc length non-uniform and to segment the arc length equally in the smooth curve. The initial cam curve of an optical system is optimized and analyzed, the results show that when the arc length is divided by the power function, the cam curve can be significantly improved, the pressure angle of the curve can be reduced, and the optimized curve is smooth and without inflection point, which can effectively improve the overall performance of the cam.

A four-layered composite silicon nitride waveguide with an asymmetric horizontal slot is proposed. The waveguide exhibits an ultra-flat and low dispersion with four zero dispersion wavelengths over an ultra-wide bandwidth. In the wavelength range from 1269 nm to 2556 nm, the dispersion varies between -3.27 and 3.29 ps/nm/km. Dispersion tailoring is studied by tuning structural parameters of the composite waveguide. Nonlinear coefficient and phasematching condition in four-wave mixing process are explored, which confirm the proposed waveguide is promising in nonlinear applications.

The optical switch is the core component of all-optical communication networks. Optofluidics is the integration of optics and microfluidics (lab on the chip). Here, based on optofluidics and optical communication technology, a 2×2 optical switch structure is proposed. The proposed switch uses a micro droplet and a microfluidic drive technology based on the electrowetting on dielectric (EWOD) to realize the optical path conversion. The optical switch has a small volume, simple structure, low power loss. Meanwhile it has no movable micromechanical elements and is easy to be operated. Here the structure and working principle of the optical switch are introduced.

In this paper, we propose a nanoscale plasmonic structure, which consists of a MIM bus waveguide coupled to a triple-cavity resonator system arranged in a T-shape. Numerical simulations by finite element method (FEM) and CMT are carried out to investigate the transmission spectra and field distribution of this special design. The results show that the PIA effect can be observed in the proposed structure with shoulder-coupling configuration. The group delay time at the center wavelength of PIA window can achieve to -0.232 ps using our proposed structure. We also dicuss the possible methods for controlling fast light characteristics. It is turn out that the PIA effect can be effectively controlled by varying the structural parameters of this plasmonic coupling system.

The grating imaging spectrometer has the characteristics of good linearity, wide dispersion range and is widely used in the field of remote sensing. Distortions (including smile and keystone) are one of the important parameters of the grating imaging spectrometer, which directly affects the quality of the image and spectral information obtained by the imaging spectrometer. In order to get the requirements of two kinds of distortions in the design process of the grating imaging spectrometer, the effect of the smile and keystone on the target detection is simulated and analyzed respectively. Based on the spectral response function with the Gaussian, the change of the spectral signal acquired by the grating imaging spectrometer with the amount of the different smile is calculated by combining with the spectral data of the atmospheric in the visible and near-infrared (0.4~1μm). The results show that the amount of smile should be no more than 1nm, 0.6nm and 0.2nm respectively when the spectral resolutions of the imaging spectrometer are 20nm, 10nm and 5nm. With the assumption that the spatial response function is the rectangle function, the effect of the different keystone on spectral signal acquisition of the imaging spectrometer is simulated by using the hyperspectral data. The results indicate that the offset of the keystone should be controlled within 0.04d (d is the pixel width).

In this paper, the generation mechanism of stray light is analyzed for a visible and near infrared imaging spectrometer with a spectral range of 400nm to 900nm. The optical mechanical model of the instrument was established and its stray light level was simulated. Based on the notch method, A stray light measuring device is built. The veiling glare index of the imaging spectrometer is measured to be 0.84%. The uncertainty of measurement is assessed by GUM method, and the influence of uncertainty components on the measurement results is analyzed. When the confidence probability of the measuring device is 95.45%, the measurement uncertainty of veiling glare index is 0.15%. Finally, a comparison and analysis are made between the simulated values of the veiling glare index and the actual measured values. This work provides technical support for the development of high resolution imaging spectrometer.

The resolution limit is one of the key performance specifications of photolithography machine. And off axis illumination is one of the important resolution enhanced technologies. The generally used illumination modes include conventional, annular, quadrupole and dipole. And their performance is expressed by the characteristic parameters. To guarantee these parameters, the pupil correction unit should be adopted. Therefore, it is necessary to study the pupil correction technology for photolithography. In order to achieve flexible pupil correction, a method with correction finger is studied, which could change the regional energy by partial blocking effect. It is available to reduce regional energy by adjusting the width and length of correction finger. As a contrast, a method with grayscale filter is also analyzed. The grayscale filter has uniform transmission distribution in every region. The higher energy region corresponds to lower transmission distribution to achieve the energy balance. The comparison of the two pupil correction methods are analyzed firstly. The analysis results show that the two methods could improve pupil performance significantly and achieve the same correction results. Furthermore, the photolithography performance simulation is implemented. The results indicate that the critical dimension (CD) and H-V bias of the corrected pupils are improved consistently compared with the uncorrected pupils. In the application perspective, the method with correction finger is more flexible because its length could be adjusted to change relative blocked energy. However, the grayscale filter has to be replaced to change its correction effect.

With the application of source mask optimization (SMO) technology in the 28nm and below nodes photolithography machine, the freeform pupil illumination technology has been widely utilized to achieve resolution enhancement for various complex patterns. The freeform illumination module (FIM) equipped with micro-mirror array (MMA) are proposed, which could realize arbitrary pupil by adjusting the angle position distribution of MMA. Therefore, it is necessary to research the freeform pupil illumination technology in immersion photolithography machine. An excellent performance optical system for FIM mainly including homogenization unit, micro-lens array (MLA), MMA and Fourier transform lens is proposed in this paper. The homogenization unit is used to increase the uniformity of the beam incident onto MMA. The beam incident onto MLA is divided and focused on MMA. The focused sub-beams are reflected by micro-mirrors and then incident into Fourier transform lens. And the freeform pupil is generated at its back focal plane. In order to verify the feasibility of the designed optical system, three freeform pupils optimized by SMO are input into the designed FIM and the corresponding simulated pupils are exported. Furthermore, the photolithography performance simulations of the optimized and simulated pupils are implemented in optical model. The results indicate that their critical dimension (CD) differences are less than 0.5nm RMS for thousands of patterns in 40nm-80nm, such as line end, line space, contact hole, end to line, SRAM et. al., which shows that the excellent performance of the designed FIM.

In the 28nm and below nodes lithography machine, the freeform pupil illumination has been widely used with the application of source mask optimization technology. As one of the most important implementations, the freeform illumination module is equipped with micro-mirror array (MMA), which can generate arbitrary pupil by adjusting its angle position. It is necessary to monitor the angle position of MMA real time for its significant function. However, there are several difficulties in the monitoring: 1) The monitoring unit could not disturb the working light path. This determines that the monitoring light should be glancing incident onto the micro-mirror; 2) The size of micro-mirror is relative small. And its rotation angle range is relative large in two dimensions; 3) There are several thousands of micro-mirrors. The crosstalk should be avoided in the monitoring method. In order to find a suitable monitoring method, the imaging and Fourier transform methods are studied. In the imaging method, the reticle is imaged onto the detector with the reflection of a single micro-mirror. The center of the reticle image is calculated to represent the angle position. In the Fourier transform method, the angular distribution of the light reflected by the micro-mirror is detected. And the angular distribution centroid is used to evaluate the angle position. In order to verify the feasibility and compare the performance of the two methods, the influences of alignment error and the scattered light are analyzed. The simulation results show that the Fourier transform method is insensitive to the scattered light and is independent to the relative position of the micro-mirror and Fourier transform lens.

In this paper, a rectangular magnetic fluid deformable mirror (MFDM) with dual-layer actuators is proposed, which is designed to improve the correction performance for full-order aberrations. The shape of the magnetic fluid surface is controlled by the combined magnetic field generated by a Maxwell coil and a two-layer array of miniature copper coils. Compared to conventional adaptive systems that use two mirrors, the proposed MFDM combines the two mirrors into one device. In order to evaluate the performance of MFDM on the correction of full-order aberrations, a decoupling control algorithm based on Zernike mode decomposition is adopted for the MFDM with dual-layer actuators. The experimental results based on a fabricated prototype MFDM show the effective correction performance of the mirror for the full-order aberrations.

Magnetic fluid deformable mirror (MFDM) is a new type of wavefront corrector that features large deformation strokes, smooth continuous mirror surface, low manufacturing cost, and easy scalability. Considering the idea of taking full advantages of the MFDM’s stroke strengths and the limitations of the adaptive optics (AO) system with the wavefront sensor, this paper proposes a MFDM based wavefront sensorless adaptive optics system. In order to make the MFDM produce desired deformation to eliminate unknown aberrations, this paper introduces the stochastic parallel gradient descent (SPGD) algorithm in the control system. Experimental results show that this SPGD algorithm can effectively control the MFDM to compensate for the unknown aberration in a parallel laser beam so that a perfect focused spot is produced on the CCD image.

Optical vortices have been applied in many fields for their distinct properties. In this paper, we explore the focusing intensity distribution of the radially and azimuthally polarized vortex beam (VB) with varying beam waist parameter. The results reveal that low beam waist parameter is beneficial to form a super-resolution spot. In the condition of the high beam waist parameter, the focusing intensity of radially and azimuthally polarized VB along the longitudinal direction would split to multi-spots. Meanwhile, the focal plane intensity distribution become non-symmetrical as well as expansion when the beam waist parameter increase. Therefore, appropriate beam waist must be chosen for the two kind beam in actually application. Furthermore, we also investigate the focal properties affected with helical phase TC. The results reveal that the focal spot size of radially polarized VB along the longitudinal gradually increases with the order of helical phase. The peak intensity ratio of the longitudinal and transverse field of radially polarized VB holds a maximum value when helical phase order l = 0 and becomes to minimum when l =1 , then gradually increases with the order of helical phase. For the azimuthally polarized VB, when l =1 , the focal intensity would exhibit an excellent small solid spot. The results obtained in this paper are useful for application of radially and azimuthally polarized VB.

Metallic glasses with unique properties, such as large plasticity within supercooled liquid region ΔT and excellent wear resistance, have attracted much attention in recent years. However, the applications of thin film metallic glass (TFMG) in optical area are seldom reported yet. Here, we proposed a reflective color filter with simple sub-wavelength nanorods fabricated with MgZnCa metallic glasses. Using the finite-difference time-domain (FDTD) methods, we systematically simulated the reflection spectra with different parameters such as the diameter and the height of nanorods. The simulation results indicate that the reflection efficiency is as high as 80%, and the color can be adjusted by changing the parameters effectively, which could be of significance for designing desirable color filters by selecting the appropriate nanostructure parameters. More importantly, the color filter facilitates the scalability to the optical application of TFMG and possesses the potential of large-scale fabrication due to the MgZnCa TFMG has low glass transition temperature (T_g) and large plasticity within ΔT.

The wheeled polishing structure with cylinders based on industrial robot is established by combining the advantages of robot control and wheeled polishing technology. It can flexibly adapt to the surface shapes of aspherical, meanwhile, based on the friction between the polishing wheel and the working surface, a high-precision surface is obtained under the control of the precise pressure. Based on Preston's Formula and Hertz's Contact Theory, using MATLAB to perform Numerical Simulation to verify that the downforce meets the Gaussian distribution, which demonstrates the feasibility of the structure. Then this paper uses MATLAB to design code programming and a reasonable running track.

As new artificial electromagnetic materials, metamaterials have unique properties compared to natural materials, such as negative refraction, invisibility, and perfect imaging. Surface plasmon-polaritons (SPPs) are electromagnetic waves travelling along the surface of the polar material SiC. Spectral selectivity, high intensity, and unidirectional emission of thermal radiation into a single desired angle have been investigated, which promises important applications such as thermophotovoltaic devices, mid-infrared light sources and thermal spectroscopy. In this work, a kind of silicon carbide (SiC) structure is designed and the corresponding thermal radiation is simulated. SiC, as a polar material, exhibits a metal-like characteristic at about 10.6 to 12.6 μm, supporting a surface phonon polariton wave in this band. Due to high melting point of silicon carbide, it can be used for thermal source design to control direction and efficiency of thermal radiation.

A reflective color filter based on the micro-cavity incorporating a nanostructure is proposed, which consists of a nano-metallic grating, a dielectric layer and an aluminum (Al) film. By varying the duty cycle of the metallic grating, red, green and blue (RGB) colors can be obtained for the transverse electric (TE) polarized incidence, having a good angular tolerance up to 30°. While these structures show different colors for transverse magnetic (TM) polarized light, and the color difference caused by polarization changes with the duty cycle chosen in different range. Therefore, the proposed structure demonstrates distinct reflections with different duty cycles, which can be utilized for reflective color displays as well as anti-counterfeiting devices.

The directions of refracted and reflected beams in gradient metasurfaces are governed by the generalized Snell’s law. The metasurface response can also be controlled dynamically by a standing wave formed by two coherent counterpropagating beams. In this work, we study sensing properties of two types of optically controlled metasurfaces. With different ambient dielectrics, the metasurface reveals a shift of coherent absorption spectrum. The thicker the dielectric layer is and the higher its refractive index ise, the more the absorption spectrum moves. Moreover, the intensities of the anomalous scattering light change with the refractive index and thickness of the dielectric layer while the radiation direction is kept unchanged.

Quartz enhanced photoacoustic spectroscopy (QEPAS) is an extremely effective tool for the detection and quantification of trace gases, which offers advantages of fast response, high sensitivity and high resolution. In this paper, a gas sensor based on quartz-enhanced photoacoustic detection and an external cavity quantum cascade laser (ECQCL) was realized and characterized for acetone measurement. Photoacoustic signal dependence on gas pressure and laser operating parameters were studied to optimize sensor performance. In addition, potential approaches and detection schemes on improving sensor performance were also discussed.

A novel anti-bending long period grating (LPG) in an embedded-core hollow optical fiber (ECOF) is proposed and experimentally demonstrated. A piece of ECOF was rotated by 180° around the geometrical center of the fiber, and then it and other ECOF were aligned along the fiber core and spliced. And a LPG, the center of which is the fusion splicing point, was fabricated in the ECOF by using a high-frequency CO₂ laser to form an anti-bending sensor. The dependence of the resonant peak on the bending was studied. Experimental results show that the maximum sensitivity of bending is only 0.47 nm/m^-1.

A modified phase generated carrier (PGC) demodulation algorithm for interferometric sensor is presented in this letter. Compared with the differential-cross-multiplying measure (PGC-DCM algorithm), the effect of light intensity disturbance (LID) is eliminated. Additionally, the harmonic distortion of arctangent measure (PGC-arctan algorithm) is well suppressed. In the experiment, while the simulated LID frequency is settled to 50 Hz, the signal-to-noise of the improved PGC algorithm respectively receives an increase of 10.3 dB and 18.2 dB over PGC-DCM and PGC-Arctan algorithms. The system has a dynamic range of 45.9 dB at 600 Hz by employing the improved PGC demodulation algorithm.

The design of birefringent photonic crystal fiber sensor based on the surface plasmon resonance model is proposed in this paper. This sensor utilizes circular air holes to introduce birefringence into the structure. The effect of geometric parameters on the performance of the sensor has been analysed with the operation wavelength between 600 nm and 800 nm. The sensor is designed to detect refractive index of the analyte between 1.33 and 1.35, which offers average sensitivity of about 4880 nm/RIU and 3940 nm/RIU for HE^x₁₁ and HE^y₁₁ modes, respectively. Moreover, the proposed sensor has a strong potential for multi-channel/multi-analyte sensing with much higher sensitivity.

A biological particle counter with a new optical system based on 405nm laser-induced fluorescence is developed. When the media is standard fluorescent particles, the fluorescence signal will be caught clearly. Further, Staphylococcus aureus are used as typical bacteria for fluorescence analysis. The results show that the counter can distinguish between fluorescent particles and non-fluorescent particles, and can differentiate between active biological particles and inactive biological particles.

A variable-spun birefringence fiber, as long as the spun rate changes slowly enough and the maximum spun rate is large enough, can realize the conversion between linearly polarized light and circularly polarized light. Environment temperature may affect the beat length of the birefringence fiber, which leads to the instability of the polarization of the fiber wave plates. According to the relation between the beat length of the fiber and the temperature, we discuss the thermal stability of variable-spun fiber wave plates with different structural parameters, and give the temperature range for qualified operation. The research results are of referential value to the design, fabrication and evaluation of the variable-spun fiber wave plates.

A low false alarm rate in smoke has always been chasing after pulse laser ranging system. Smoke distributes particularly random in space so that different smoke distributions produce distinct interference echoes even if they are under same attenuation degree. Based on the theory of single scattering, in this paper the echo-element superposition model is established to study the relationship between smoke backscattering pulse and smoke thickness under the condition of same attenuation but different spatial distribution. The analysis shows that at a constant threshold, the pulse width of backscattered echoes in smoke are first broadened logarithmically by the thickness of the smoke and then compressed to zero with a negative exponential relationship, while a maximum width appears in the process; the peak of the backscattered echoes gradually decreases with the inverse of smoke thickness. In order to validate the model, the Monte Carlo method for photon tracing is used to simulate the model. The simulation results are in good agreement with the theoretical analysis. At the same time, an experimental device is set up in which pulse laser is transmitted in the smoke environment. Experimental results show that with the detection distance, one-way attenuation, transmitted pulse width of 25m, 60%, 20ns respectively, the pulse width of target echoes remains basically unchanged while smoke thickness varies, and the peak value and pulse width of the backscattering pulse are consisted with theoretical analysis within an error of 5%. This results can be used for laser ranging system in low-visibility environment for interference suppression and reducing false alarm rate, so as to improve system stability and anti-interference ability.

Fiber wave plates are usually used for the transformation of polarization state in fiber sensing systems. Environment temperature and operating wavelength may influence the beat length of the birefringence fiber, inducing the instability of fiber wave plates on polarization transforming. As for the variable-spun fiber wave plate with different structure parameters (fiber length, spun rate profile and maximum spun rate), this paper describe the effect of beat length on the equivalent phase retardation. The proper range of the beat length for the qualified fiber wave plate is calculated by the differential phase retarder cascade model. The results are of referential value to the design, fabrication and evaluation of the variable-spun fiber wave plate.

A novel distributed optical fiber disturbance sensing system based on a feedback semiconductor laser and a fiber-ring as a self-mixing interferometer is proposed and demonstrated. When an external disturbance acts on the sensing fiber, a phase change in the light beam propagating in the fiber-ring will be induced, which in-turn is converted into an intensity modulation in the laser output through a feedback light interference in the laser and a nonlinear optical amplification by the laser. The sensor output signals can be obtained directly from the laser module equipped with an internal photodiode. The primary experiments were carried out and the results show that the RMS value of output electrical signal has a linear relation with the disturbance position, so this feature can be utilized as a means of localizing disturbances along the sensing fiber. The maximum location error obtained in our experiments is about 27 m within a 1-km long sensing fiber. Therefore, the proposed sensing system and location method are feasible. Moreover, the system is high in the sensitivity and simple in the structure as well as in signal processing.

Water vapor content and aerosol concentration will affect detection capability of wind lidar. Types and concentrations of aerosols in coastal region are different from those in inland, and the air is more humid, which makes the wind field monitoring capability of lidar in coastal region deeply concerned. In this paper, the Chinese new all-fiber coherent lidar and radiosonde dataset was collected from the First wind field joint monitoring test in coastal region, and meteorological and aerosol dataset came from Local Meteorological Bureau. By comparing detection results of lidar and radiosonde, analyzing detection precision and maximum detection distance of lidar, and validating capture capability of lidar for typical wind field characteristics in coastal region, reliability and performances of this new wind lidar under clear-air, cloudy, foggy, hazy and precipitation conditions were analyzed in detail. The results show: In different weather conditions, lidar have high detection precision. Horizontal wind speed accuracy of lidar is not greater than 0.5 m/s, and horizontal wind direction accuracy of which is not greater than 5 degrees. Maximum detection distance of lidar are different, best in hazy conditions, and worst in precipitation because of attenuation; In different weather conditions, the dataset correlation coefficient between lidar and radiosonde can reach up to more than 0.95; High data resolution and strong sensitivity make lidar stably monitor typical wind field in coastal region, such as formation and disappearing of haze and foggy

Variable-spun fiber wave plate can be used to change the polarization state in fiber optic sensing systems. However, the beat length of the birefringence fiber may variation with different operating wavelength, which further leads to the instability of the polarization transforming performance. Based on the relation between the beat length and the operating wavelength, the wavelength sensitivity is simulated for the variable-spun fiber wave plate with different structural parameters (fiber length, spun rate profile and maximum spun rate). The achromatic bandwidth of the qualified fiber plate is discussed. The results have certain reference value for the design, fabrication and evaluation of variable-spun fiber wave plate.

Elasticity and viscosity of biological tissue are closely correlated with their pathological changes. However, there is no effective method to measure the elastic and viscous property of tissue. Optical coherence elastography (OCE) utilizing optical coherence tomography (OCT) as imaging engine can assess localized mechanical properties of tissues with microscale resolution. Shear wave OCE was recently proposed to obtain the elastic modulus of linear elastic materials by detecting the shear wave speed. When traveling in viscous material, the propagation velocity of shear wave is related to the frequency of the wave and the viscoelasticity of tissue. In this paper, shear wave OCE experimental method was developed to measure the elasticity and viscosity of tissue simultaneously. Shear wave was generated by a pin fixed on a piezo stack, which was driven by a series of square wave pulses with various frequencies. OCT phase analysis method was developed to detect the dispersion of the shear wave propagation speed at multiple frequencies. The shear wave velocities were then fitted to the analytical solution of a Voigt model to solve the elastic modulus and viscosity. The measurement results of a phantom obtained by the proposed method were comparable to the results obtained by uniaxial testing, which demonstrated the effectiveness of the shear wave OCE method. Shear wave OCE is nondestructive and easy to use and has the potential to be further developed to measure the complex mechanical properties of soft materials.

Fourier ptychographic microscopy (FPM) is a wide-field and high-resolution (HR) imaging technique, reconstructing HR spectrum from a series of low-resolution (LR) images captured at different illumination angles. In FPM, the quality of captured images is a critical factor that affects the final reconstruction HR result, so an effective denoising method is an indispensable process step. Here we propose an adaptive denoising method for FPM, which takes advantage of the data redundancy of FPM to separate signal from noise without any pre-knowledge about the noise statistics. Different from the traditional denoising method by reducing a fixed threshold, the proposed adaptive denoising method can more effectively eliminate noise and preserve more effective signals. This paper explains adaptive denoising principle and process steps, and finally demonstrates that this method not only improve the accuracy and robustness of FPM, but also relax the imaging performance requirement for implementing high-quality FPM reconstruction.

We demonstrate an efficient quantitative phase imaging (QPI) approach using programmable annular LED illumination. As a new type of coded light source, the LED array provides flexible illumination control for noninterferometric QPI based on a traditional microscopic configuration. The proposed annular LED illumination modulates the transfer function of system by changing the LED illumination pattern, which provides noiserobust response of transfer function and achieves twice resolution limit of objective NA. The quantitative phase can be recovered from slightly defocused intensity images through inversion of transfer function. Moreover, the weak object transfer function (WOTF) of axis-symmetric oblique source is derived, and the noise-free and noisy simulation results validate the predicted theory. Finally, we experimentally confirm accurate and repeatable performance of our method by imaging cellular specimens with different NA objectives.

Deep learning is an extension of machine learning,deep learning uses multilayer neural networks to analyze data[1,2].Convolutional Neural Networks (CNN) is a commonly used neural network structure in deep learning. It is widely used in various fields, especially in the field of machine vision. In the field of optics,Monochromatic aberrations include spherical aberration, coma, astigmatism, defocus and so on, the common way to interpret interferograms is the Zernike polynomials, it generally used to describe the wavefront characteristics.In this paper, the convolutional neural network algorithm is used to identify astigmatism and defocus of the typical monochromatic interferograms, Zernike polynomial is multiplied by the aberration coefficient to represent the wavefront, the wavefront into the light intensity formula to obtain the aberration interferogram, the use of the above method to obtain the defocus interferogram, the result shows that the recognition accuracy is very high.The method of deep learning algorithm used to identify monochrome interferograms is simple and fast, and the training samples do not need manual calibration.

In this work, we evaluated the feasibility of sapphire conductive cooling for short-pulse Ti:Sapphire (Ti:sa) laser amplifiers which suffers from thermal issues under high-repetition-rate and high-energy operation. Numerical heat transfer simulations of 100-TW class sapphire face-cooled Ti:sa gain modules operated around 300 W average powers are presented. The distributions of temperature, stress, strain, and birefringence in liquid cooled sapphire/Ti:sa/sapphire assembly are calculated by a finite element analysis. Based on these data, the thermal induced wave front distortions and depolarization are investigated for different repetition rates. We determine that sapphire face cooling concept holds a promise of achieving higher energies and repetition-rates in Ti:Sa amplifiers.

We study the interaction of a stationary election and a tightly focused ultra-short ultra-intense laser pulse in vacuum. Ponderomotive force accelerates an electron at the focus of diverse intensity tightly focused short-pulse laser is considered. When the laser pulse intensity is small, the election is in the spiral motion of the laser pulse center. In order to accurately control accelerated electron, we research the relationship between deviation angle of electron and laser intensity when the separation of the electron and the laser pulse. It is found that the tendency of deviation is up, then down and then up again with the increasing of laser intensity. They are not a linear relationship. If we want to get collimated high energy electron, the laser intensity must be in a specific segment interval.

We present a passively mode-locked erbium-doped fiber ring laser with near-zero net cavity dispersion using the nonlinear polarization rotation technique. The compact all-fiber laser is constructed by utilizing an optical integrated component. Through optimizing the cavity dispersion and nonlinearity, high-peak-power near-transform-limited pulses with a spectral width beyond the gain bandwidth limitation can be directly obtained from the laser. Resultant output pulses have a pulse duration of 62 fs, a 3-dB spectral width of 66.3 nm, and a maximum peak power of 7.9 kW. Numerical simulations reproduce the generation of sub-100-fs pulses in the laser. The pulse-shaping mechanism can be attributed to simultaneous dispersion and nonlinearity management in the cavity, which is distinct from that in the stretched-pulse lasers.

The terahertz Gabor inline holographic reconstructed images have the characteristics of large backgrounds and small targets, which are different from the standard images of conventional research. Thus, we carried out the connected area disposal method before the Weighted Nuclear Norm Minimization (WNNM) in this paper. Connected area disposal can split the image into multiple independent regions to denoise the large background. The WNNM denoising method can preserve the details of the targets well. The numerical analysis and experimental researches of the denoising results proved that the proposed method in this paper can get a better denoising effect than WNNM algorithm alone.