Janis Joplin once said, “Don’t compromise yourself; you are all you’ve got.” I like her quote and I agree with it when it comes to how we treat ourselves, how we treat others, and how we see ourselves. Everything else in this world is negotiable and it should be. I like another quote by Winston Churchill, “The English never draw a line without blurring it.” In this case, I would like to thank the English for making the world a better place.

This PDF file contains the editorial “OE 2012 List of Reviewers” for OE Vol. 52 Issue 04

A new four-step phase-shifting method for birefringence measurement based on the plane polariscope is proposed. The plane polariscope to carry this phase-shifting method is characterized by triple polarizers. One fixed polarizer is used as a linearly polarized state generator; the other two rotatable linear polarizers act as phase shifters. The measurement ranges are (0, π ) for phase retardation and (−π/4 , +π/4 ) for azimuth angle. Numerical simulation is carried out, and two mica wave plates are tested and evaluated. Compared with other commonly used methods on Senarmont or circular polariscopes, this method has the simplest optical setup and also is free from the errors of quarter wave plates. It has less wavelength dependence and temperature dependence and is expected to be more cost-effective and environmentally robust.

In an optical burst switching core node, each output port is equipped with a different network interface unit that can provide a specific data rate. Bursts will use different probabilities of select output ports, which is in accordance to the path-length metric-based routing optimal algorithm and wavelength resource situation. Previous studies ignore this issue. We establish a burst-outputted model considering the different service rate of output ports and different port-selected probabilities. We calculate burst-blocking probability and analyze the relationship between service rate and output-port-selected probability in detail.

Search and detection are two everyday jobs of many biological systems, performed almost innately, either consciously or subconsciously and necessary for survival. Search and target detection, in particular, are the first stages in visual observation tasks associated with military target acquisition, industrial inspection, traffic control, and many more applications. These tasks currently are often performed with the aid of an electro-optic viewing system. In these tasks, search is defined as the process by which an observer surveys his surroundings, and detection is the process of successfully declaring a desired target as such—more precise interpretations of these terms will be found in what follows and in the included papers.

Hundreds of simple target-detection algorithms were tested on mid- and long-wave forward-looking infrared images. Each algorithm is briefly described. Indications are given as to which performed well. Most of these simple algorithms are loosely derived from standard tests of the difference of two populations. For target detection, these are populations of pixel grayscale values or features derived from them. The statistical tests are implemented in the form of sliding triple window filters. Several more elaborate algorithms are also described with their relative performances noted. They utilize neural networks, deformable templates, and adaptive filtering. Algorithm design issues are broadened to cover system design issues and concepts of operation. Since target detection is such a fundamental problem, it is often used as a test case for developing technology. New technology leads to innovative approaches for attacking the problem. Eight inventive paradigms, each with deep philosophical underpinnings, are described in relation to their effect on target detector design.

We present a new method to derive a multiscale urban camouflage pattern from a given set of background image samples. We applied this method to design a camouflage pattern for a given (semi-arid) urban environment. We performed a human visual search experiment and a computational evaluation study to assess the effectiveness of this multiscale camouflage pattern relative to the performance of 10 other (multiscale, disruptive and monotonous) patterns that were also designed for deployment in the same operating theater. The results show that the pattern combines the overall lowest detection probability with an average mean search time. We also show that a frequency-tuned saliency metric predicts human observer performance to an appreciable extent. This computational metric can therefore be incorporated in the design process to optimize the effectiveness of camouflage patterns derived from a set of background samples.

Prior work has shown that the masked target transform volume (MTTV) clutter metric provides a measure of scene clutter that better correlates to measured probability of detection for human observers than several previously published clutter metrics. Several factors involved in using the MTTV to assess clutter in imagery are discussed here. A previously published modification to the MTTV metric to provide a normalized output value comparable across different image sets regardless of scene size is reviewed. Initial MTTV development required knowledge of a scene's target signature and produced an unbounded metric value. Metric behavior is discussed for the case in which an average of several target signatures is used in place of a specific target signature. This allows the MTTV to be calculated for images that do not contain a target. It is shown that the user may trade computational efficiency with metric accuracy to suit a particular application. The sensitivity of the metric to variations in image noise level, target segmentation error, and viewing distance are also presented.

For many military operations, situational awareness is of great importance. During night conditions, this situational awareness can be improved using both analog and digital image-intensified cameras. The quality of image intensifiers is a topic of interest. One of the differences between a digital and analog system is noise behavior. For digital image intensifiers, the noise behavior is not as good as for analog image intensifiers, but it can be improved using noise-reduction techniques. In this paper, the improvement using temporal noise reduction and local adaptive contrast enhancement is shown and quantitatively evaluated by subjective measurement of the conspicuity and triangle orientation discrimination (TOD). The results of the conspicuity and TOD experiments are consistent with each other. The highest improvement is found for a low-clutter environment; for medium- and high-clutter environments, the improvement is less. This can be explained by the fact that image enhancement increases contrast of all image details, irrespective of whether they are targets or clutter. For low-clutter image enhancement, target conspicuity and target detection improvement will be largest, since there are not many distracting elements.

We investigate how human visual search performance with field of view (FOV) restrictions depends on scan speed, zoom factor, target location, and conspicuity. First, observers search a FOV that moves at a constant speed along a predefined path over a visual search scene (the field of regard, or FOR), and we measure the effects of scan speed, zoom factor, FOV size, target location, and conspicuity on search performance (detection time and probability). Then observers search either visual or thermal scenes by freely moving a joystick-controlled FOV over the FOR, while freely selecting the zoom factor in some conditions, and we measure the effects of the scan path characteristics and the use of different strategies on search performance. Search performance depends on the effective FOV size (the area where targets are expected to occur), but is largely independent of the display area. Both for visual and thermal imagery, various search performance measures correlate with target conspicuity. The results of both experiments suggest that observers can optimize their performance by adjusting their scanning behavior both to their visual limitations and to the expected target conspicuity. We present the outlines of a simple search model based on these current findings.

The probability P(t) of target acquisition, for a single observer who has unlimited time to search a field of view (FOV) for a single target, is expressed in terms of search parameters P ∞ and τ under conditions where these parameters are independent of time. It has been assumed that P ∞ has been determined for a particular target, scene clutter and imaging system and, for a given scenario, τ is determined empirically from P ∞ . The equation for P(t) is then extended to include time-limited search and field of regard (FOR) search, where it is assumed the target has an equal probability of being anywhere in the FOR. Equations are derived for the mean time to find a target for two cases: (1) an arbitrary number of observers using a single sensor search a single FOV or FOR for a single target; (2) two observers using two sensors search independently for a single target. The condition that P ∞ and τ be independent of time is relaxed and this leads to the time dependent search parameter (TDSP) search model. The TDSP search model is used to calculate P(t) in: (1) search from a moving vehicle, (2) FOR search where the condition that the target has an equal probability of being anywhere in the FOR is relaxed, and (3) in multitarget search.

For more than 50 years, the U.S. Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate (NVESD) has been studying the science behind the human processes of searching and detecting, and using that knowledge to develop and refine its models for military imaging systems. Modeling how human observers perform military tasks while using imaging systems in the field and linking that model with the physics of the systems has resulted in the comprehensive sensor models we have today. These models are used by the government, military, industry, and academia for sensor development, sensor system acquisition, military tactics development, and war-gaming. From the original hypothesis put forth by John Johnson in 1958, to modeling time-limited search, to modeling the impact of motion on target detection, to modeling target acquisition performance in different spectral bands, the concept of search has a wide-ranging history. Our purpose is to present a snapshot of that history; as such, it will begin with a description of the search-modeling task, followed by a summary of highlights from the early years, and concluding with a discussion of search and detection modeling today and the changing battlefield. Some of the topics to be discussed will be classic search, clutter, computational vision models and the ACQUIRE model with its variants. We do not claim to present a complete history here, but rather a look at some of the work that has been done, and this is meant to be an introduction to an extensive amount of work on a complex topic. That said, it is hoped that this overview of the history of search and detection modeling of military imaging systems pursued by NVESD directly, or in association with other government agencies or contractors, will provide both the novice and experienced search modeler with a useful historical summary and an introduction to current issues and future challenges.

Satellite laser retroreflector (LRR) array is an essential reflecting element for satellite laser ranging. Because of the requirements of manufacturing and assembling, the actual LRR reflecting face is placed underneath the top of assembly. We use the ray tracing method to build up the active retroreflecting region model for LRR with a structural recession effect. Combined with the principle of far-field diffraction intensity and velocity aberration, we give the mathematical model for expressing the structural recession effect on the received optical signal intensity (ROSI) by a ground station. As an important factor for determining the performance of LRR, the distribution of ROSI is simulated for an HY-2A LRR array. The simulation shows that the value of ROSI decreases along with the increment of structural recession size. The bigger optical incident angle should bring about further reduction of ROSI. Only considering the structural recession effect on ROSI, we obtain the regularity of difference of range correction. Before and after considering the structural recession effect, the maximum difference of range correction reaches 9.36 mm for the whole incidence condition. It demonstrates that structural recession cannot be ignored for deciding the performance of LRR.

Three-dimensional (3D) micro/nano-manipulation using optical tweezers is a significant technique for various scientific fields ranging from biology to nanotechnology. For the dynamic handling of multiple/individual micro-objects in a true 3D working space, we present an improved hybrid optical tweezers system consisting of two multibeam techniques. These two techniques include the generalized phase contrast method with a spatial light modulator and the time-shared scanning method with a two-axis steering mirror and an electrically focus-tunable lens. Unlike our previously reported system that could only handle micro-objects in a two and half dimensional working space, the present system has high versatility for controlled manipulation of multiple micro-objects in a true 3D working space. The controlled rotation of five beads forming a pentagon, that of four beads forming a tetrahedron about arbitrary axes, and the fully automated assembly and subsequent 3D translation of micro-bead arrays are successfully demonstrated as part of the 3D manipulation experiment.

Passive imaging offers covertness and low power, while active imaging provides longer range target acquisition without the need for natural or external illumination. This paper describes a focal plane array (FPA) concept that has the low noise needed for state-of-the-art passive imaging and the high-speed gating needed for active imaging. The FPA is used with highly efficient but low-peak-power laser diodes to create a night vision imager that has the size, weight, and power attributes suitable for man-portable applications. Video output is provided in both the active and passive modes. In addition, the active mode is Class 1 eye safe and is not visible to the naked eye or to night vision goggles.

On a moonless night, the primary source of natural illumination in the near infrared and short-wave infrared spectral bands is airglow. We use data gathered by astronomers and atmospheric scientists to estimate the magnitude and variability of airglow ground illumination. Based on that foundation, we analyze the target acquisition performance of imagers that use silicon and indium-gallium-arsenide focal plane arrays.

The anaglyph three-dimensional (3D) method is a widely used technique for presenting stereoscopic 3D images. Its primary advantages are that it will work on any full-color display and only requires that the user view the anaglyph image using a pair of anaglyph 3D glasses with usually one lens tinted red and the other lens tinted cyan. A common image quality problem of anaglyph 3D images is high levels of crosstalk–the incomplete isolation of the left and right image channels such that each eye sees a “ghost” of the opposite perspective view. In printed anaglyph images, the crosstalk levels are often very high–much higher than when anaglyph images are presented on emissive displays. The sources of crosstalk in printed anaglyph images are described and a simulation model is developed that allows the amount of printed anaglyph crosstalk to be estimated based on the spectral characteristics of the light source, paper, ink set, and anaglyph glasses. The model is validated using a visual crosstalk ranking test, which indicates good agreement. The model is then used to consider scenarios for the reduction of crosstalk in printed anaglyph systems and finds a number of options that are likely to reduce crosstalk considerably.

In imaging systems based on compressed sensing, error in the measured data is incurred due to the nonlinear response of the photo detector, which affects the quality of the reconstructed images. We propose an algorithm to compensate the nonlinear response from the detector. The compensation is based on the detector response curve on the measured data. The theoretical analysis and simulation results show that this algorithm can greatly reduce the reconstruction errors caused by the detector’s nonlinear response. Furthermore the peak signal-to-noise ratio of the reconstructed image and the system reconstruction rate have been significantly improved, while the fine feature of the images is better preserved and reconstructed as compared to that without using the algorithm.

We propose and demonstrate a wireless optical energy transmission using optical beamforming with a spatial light modulator. We demonstrate an optical beamforming technology to focus the light of an optical source on a desired target, which can be used in various applications. Our experiment shows a wireless energy transmission efficiency of 1.3% with a white light-emitting diode light source. Although the transmission efficiency is currently low in our experimental result, we expect that the transmission efficiency can be improved up to 30% with highly efficient devices. We also propose an algorithm based on the optical beamforming to detect the location of the target device automatically. The proposed wireless optical energy transmission has several advantages over the previous wireless energy transmission methods.

Retina-like sensors maximize both field of view and resolution in addition to economizing on pixel count, so they play an important role in both biological and machine vision. A new retina-like sensor model for compensating motion blur introduced by forward motion imaging is proposed. Next, the determination of pixel arrangement of a retina-like sensor according to visual task requirements is formulated into a multiobjective optimization problem. Then, three retina-like sensors are designed to meet different visual task requirements using the particle swarm optimization algorithm. The results are robust and approximate to design criteria.

Nanoparticle jet polishing (NJP) is presented as a posttreatment to remove magnetorheological finishing (MRF) marks. In the NJP process the material is removed by chemical impact reaction, and the material removal rate of convex part is larger than that of the concave part. Smoothing thus can progress automatically in the NJP process. In the experiment, a silica glass sample polished by MRF was polished by NJP. Experiment results showed the MRF marks were removed clearly. The uniform polishing process shows that the NJP process can remove the MRF marks without destroying the original surface figure. The surface root-mean-square roughness is improved from 0.72 to 0.41 nm. power spectral density analysis indicates the surface quality is improved, and the experimental result validates effective removal of MRF marks by NJP.

We present a novel solution to accurately recover three-dimensional dynamic flame temperature field. Traditional flame temperature field reconstruction schemes take flame images with general industrial cameras and reconstruct flame temperature field under the assumption that the cameras can capture the full spectrum. However, the dynamic range of the general industrial camera is more restricted than that of the light from flame and camera response band is much narrower compared with the full spectrum. In this paper, we use high dynamic range to take flame images and reconstruct the flame radiant existence field on camera response band. Temperature field is calculated from radiant existence field via lookup table between them. Experimental results on real flame demonstrate that our approach is accurate and easy to implement. The rendering results of the flame-based temperature field accord with physical facts.

In the structured light three-dimensional measurement system, calibration is the key to the measurement accuracy; however, conventional calibration methods for the projector are either too complex or inaccurate. Therefore, we propose a simple and accurate method to calibrate the projector. In this method, the calibration points in the camera image plane can be mapped to the projector according the homography of the planar projection. In addition, an error surface compensation method is developed to minimize mapping errors caused by lens distortion of the camera and projector. As a result, the projector can be calibrated with the same method as the camera. Experiments are conducted to verify the effectiveness of the proposed method.

The noncomplete compensated calibration errors of a fiber optic gyro (FOG) can remain in the navigation stage, leading to decreased navigation accuracy. A new approach is presented to calibrate the FOG drift and scale factor error based on a double calculating program. Using an analysis of the relationship between the FOG error and misalignment, a FOG calibration error model is derived, and a three-step six-position calibration path is analyzed. In this method, the FOG drift and scale factor error are calculated from two groups of attitude information, which are resolved, respectively, from calculating programs A and B in the navigation computer. The input signal of these two calculating programs is measured from one FOG. Its effectiveness is demonstrated by simulation and turntable experiments. The results show that this method can further compensate the residual calibration errors with misalignments, thereby improving the FOG calibration accuracy.

Based on the principle of laser-linear array charge-coupled device (CCD) detection technology, a high accuracy nontouch on-line system for monitoring roller wear is brought forward. The principle and composition of the laser-linear array CCD detection system and the operation process were expatiated. Aiming at the errors of the roller’s axes shifting during the detection process, compensating steps were adopted from the vertical and the parallel direction to the detection surface. This effectively enhanced the accuracy of the detection system. Experiments proved that the accuracy of the system could reach the demand of the practical production process. It provides a new method for high speed, accuracy, and automatic on-line monitoring of roller wear. r shapegear array CCD detection. A simulation-software program is also compiled based on this principle. By using this program, the I/O signals’s data for this system is gained and the detection curves can be drawn automatically.

A classical iterative Lucy-Richardson (LR) inversion algorithm used for recovering particle-size distributions (PSD) from light-scattering data is proposed. The convergence of iteration is validated in the numerical simulation for three different distributions: the gamma, the log-normal, and the Rosin-Rammler. The accuracy of the inversion is checked graphically against the exact distribution with good results, even for the synthesized intensity data of a signal-noise-ratio smaller than 20 dB. Finally, an experiment with linear charge coupled device as the detector is carried out, and the PSD is recovered successfully by the LR inversion method.

Classically gated infrared (IR) detectors have been implemented using charge-coupled devices (CCD). Bipolar complementary metal-oxide semiconductor (BiCMOS) technology emerged as a viable alternative platform for development. BiCMOS technology has a number of advantages over CCD and conventional CMOS technology, of which increased switching speed is one. The pixel topology used in this work is a reversed-biased diode connected heterojunction bipolar transistor. The disadvantage of CMOS detectors is the increased readout noise due to the increased on-chip switching compared to CCD, which degrades dynamic range (DR) and sensitivity. This yields increased switching speeds compared to conventional bipolar junction transistors. Sensitivity improved from 50  mA/W (peak) at 430 nm in CCD detectors to 180  mA/W (peak) (or 180,000  V/W ) at 665 nm in BiCMOS detectors. Other CMOS IR detectors previously published in the literature showed sensitivity values from 2750 to 5000  V/W or 100  mA/W . The DR also improved from 47 and 53 dB to 70 dB. The sensitivity of conventional CCD detectors previously published is around 53  mA/W . The second advantage is that detection in the near-IR band with conventional silicon integrated technology is possible. This work has shown increased detection capabilities up to 1.1 μm compared to Si detectors.

A wideband tunable filter with a complex coefficient is proposed and demonstrated. The output of a polarization modulator is filtered by the optical bandpass filter, an optical single sideband modulation will be generated. When it passes through a polarization controller and a polarizer, a complex coefficient will be achieved by tuning the angle of the polarization controller before the polarizer, and the real coefficients are controlled by the optical power of the lasers. As the real coefficients and complex coefficient can be tuned, a two-taps incoherent photonic microwave filter with a tunable range over the entire full free spectral range is realized by adjusting the polarization angle from −90  deg to 90 deg while the shape of filter remains unchanged.

A widely tunable optical filter was designed and demonstrated by configuring two spatially distributed cholesteric liquid crystals (LCs) in a reflection mode, in which the incident light was first reflected by one cholesteric LC and then by the other. The spatially distributed cholesteric LCs were fabricated by injecting four cholesteric LC mixtures with different chiral concentration into the same LC cell one by one, in which the spectral position of the reflection band is spatially changed from blue to red color from one side to the other side. Using this method, a tunable optical filter with the ability of tuning the central wavelength from ∼480 to ∼613  nm and FWHM from ∼10 to ∼80  nm was successfully demonstrated.

We demonstrate an erbium-doped fiber laser passively mode-locked by few layers of graphene prepared by the mechanical exfoliation of the high oriented pyrolytic graphite through the Scotch-tape method. This all-fiber ring cavity delivered a pulse train with a repetition rate of 1.646 MHz and pulse duration of 1.656 ps. By continuously adjusting the laser cavity parameters, one can observe various soliton patterns, such as ordered-, chaotic-, bunched-, and harmonic-multisoliton state. This evidenced that a mode-locked fiber laser based on graphene saturable absorber indeed provided a well-controlled nonlinear optics platform for soliton dynamics study.

We outline an all-optical and noncontact approach for controlled laser heating and measurement of the resultant temperature distribution at the surface of a material, respectively. We show how the boundary conditions of the heating problem may be controlled optically through shaping of the pump light and use the examples of both Gaussian and flat-top beams. These two beams, together with appropriate nonoptical boundary control, allow for the laser-induced thermal study of materials with and without thermal stress. We illustrate the technique on an industrial diamond sample where a gradient and uniform temperature profile on the surface of the diamond was successfully created and measured. We use the technique to study the thermally induced degradation of industrial diamond in a controlled manner.

A model containing an inclusion matrix heated by a millisecond laser is proposed to calculate temperature and thermal stress fields of K9-glass using a finite element method. First, the evolution of temperature and thermal stress fields is analyzed. Results show that both the upper and lower surfaces are damaged. K9-glass is primarily damaged by the combination of radial and axial stresses. Calculated damage morphology is mainly determined by radial stress. Then damage morphology evolution with the increase of the incident laser energy is investigated, which shows that damage area spreads inward from both the front and rear surfaces. Finally, experimental results of long-pulse laser damage of K9-glass are analyzed. The comparison of numerical results with experimental observations shows a good correlation in damage morphology, which indicates that the built inclusion matrix model is applicable to long-pulse laser damage in K9-glass.

We propose and investigate a refractive index (RI) sensor consisting of a combination of single-multi-single mode fiber and a microslot structure in the multimode fiber fabricated by femtosecond laser as the sensing head. The beam propagation method is utilized to simulate the microslot structure. Simulation results show the size of the microslot significantly influences the RI sensitivity. At an ablation depth of 170 μm and a width of 30 μm, the refractometer shows a high sensitivity of 1327.27 nm per RI unit (RIU) and a better stability in the RI range of 1.33 to 1.35. Moreover, higher sensitivity in a narrow RI range can be achieved by optimizing the microslot structure. Experimental investigations demonstrated a sensitivity of 912.31  nm/RIU for an RI range of 1.33 to 1.35 for a refractometer with a microslot depth of 170 μm and width of 24 μm, which is essentially in agreement with the simulated results.

Salinity and turbidity are two important seawater properties in physical oceanography. The study of physical oceanography requires a compact high-resolution in situ salino-turbidimeter to measure these two parameters in different ocean zones. Refractometry has proved to be an effective method to measure seawater salinity with a high resolution. Previous studies have shown that the transmission and scattering of light in a turbid medium impact the light beam deviation measurements, which makes the combination of salinity and turbidity measurements with the same sample mandatory. We analyze the requirements and challenges of a refracto-turbidimeter design from their measurement principles and correlations. According to these requirements, we propose a miniature refracto-nephelo-turbidimeter with a charge-coupled device, providing a salinity measurement resolution of 2  mg⋅kg⁻¹ and a turbidity measurement resolution of 1% of the measurement range. Based on this refracto-nephelo-turbidimeter, different embodiments are discussed to meet the different requirements for different ocean zones.

Methods to improve the performance of the surface plasmon resonance array sensor at ambient temperature are studied. A self-reference channel was used to eliminate the long-term drift caused both by the temperature and the light source. The Hilbert–Huang transform-based signal post-processing algorithm was employed to improve the signal-to-noise ratio and reduce high-frequency noise. Finally, an adaptive moving-average method was adopted to reduce noise while preserving important high-frequency signal characteristics. A combination of these methods decreased the baseline noise to 3.6×10⁻⁶ refractive index unit. Acceptable repeatability was achieved with relative standard deviation 2.20% (n=8 ). The limit of detection of NaCl was measured at 69  mg/L .

This paper presents a simple fabrication method for a liquid-core optofluidic waveguide and demonstrates efficient light delivery and collection using optical fibers pressure-sealed into a polydimethylsiloxane matrix. Total optical loss as small as 3 dB from an input optical fiber with a core diameter of 9 μm to an output optical fiber with a core diameter of 62.5 μm connected one to another via a 2 cm long liquid-core optofluidic channel is achieved. This strategy allows rapid prototyping of optofluidic waveguides without requiring expensive microfabrication facilities and is suitable for applications that require an efficient optical sensing in a small liquid sample. As a demonstration, we examine the optical Faraday rotation of a fluid sample and identify advantages and limitations by comparison to a macroscopic system of similar length.

An electro-optic polymer waveguide modulator based on both Pockels and Kerr effects has been demonstrated. A conjugated polymer, poly (9,9-dioctyl-2,7-fluorene-co-benzo [c][1,2,5]thiadiazole-co-9-hexyl-3,6-carbazole), which has the delocalization of p-electrons and a push-pull structure along the main conjugated chain, exhibits the Pockels effect and still maintains the Kerr effect after corona-poling. By applying a direct current (DC) bias, the optical output of the modulator is roughly linearly to a modulation voltage, and the modulation depth is improved with the DC bias at fixed modulation voltage. The proposed modulator achieves a 2.18% modulation depth with 5 V p-p modulation triangular voltage and 90 V DC bias at 100 kHz by employing both the Pockels effect and Kerr effect.

A general model in satellite-to-ground quantum communication is proposed by investigating the effect of a laser acquisition, pointing, and tracking (APT) system on the polarization state of single photons. The eccentricity of the general model ranges from 0 to 1, which means that a circular orbit can be introduced reasonably. Moreover, the geocentric-equatorial coordinate system, which can utilize the two-line elements, is used in the general model. Two kinds of simulations are performed, and we found that the rotations of polarization state are obviously influenced by the APT system. Our model could be applied in a realistic satellite-to-ground quantum communication system.

A principle-of-concept demonstration about the effect of filter parameters on the output performance of a highly nonlinear fiber-based all optical thresholding technique (OTT) is proposed. The center wavelength, bandwidth, and rejection parameters of an optical bandpass filter (OBPF) used in fiber-based OTT are discussed. Carefully adjusting each parameter of the OBPF allows a steeper transforming characteristic of optical thresholding, and a fourth-order polynomial power transfer function is achieved, which is the steepest thresholding curve ever reported. To the best of our knowledge, this is the first demonstration of fiber-based OTT focusing on OBPF parameters, which makes the thresholder more flexible and allows customization of thresholding performance to meet requirements in various systems.

A novel design of a photonic crystal fiber is presented. A nearly zero dispersion regime of operation has been achieved by using a three-fold symmetry core, which is improved by the avoidance of high-index doping in a central region. The core consists of pure silica surrounded by three fluorine-doped regions and three airholes. It can be confirmed by the numerical simulations using the finite difference frequency domain method that flattened dispersion characteristics upon wavelength over the range of 1250 to 1700 nm can be achieved in an optical fiber. Further, the potential fiber geometry imperfections caused some concern. Finally, the presented fiber design is compared to selected fiber designs with a dispersion close to zero.

Fiber Bragg grating written in polarization-maintaining fiber is strongly polarization-dependent, and its spectral character depends on the polarization state of light that interrogates the grating. We propose a novel and practical method to test the spectra character of the polarization-maintaining fiber Bragg grating (PM-FBG) interrogated by a linearly polarized light with a different azimuth for the first time. We specially designed a splice with a different angle in the system to alter the azimuth of the input linearly polarized light. Using this method, we got the transmission and reflection spectra of the PM-FBG measured at different splice angles and then the experimental results were analyzed originally. The analysis result shows that the relationship between the transmission dip and the splice angle obeys the Gaussian distribution. The reflectivity of the two wavelengths of the PM-FBG depends on the azimuth of the input linearly polarized light.

Burst segmentation (BS) is a high-efficiency contention resolution scheme in bufferless optical burst switching (OBS) networks. A prioritized BS scheme for quality of service (QoS) support is developed. Unlike the existing work on the BS scheme, the proposed BS model considers path-correlated factors, such as path length, the adjoining paths carrying traffic on a given path, and the multipriority traffic coming from all paths. Byte loss probability for high-priority and low-priority bursts under the time-based assembly approach and the length-based assembly approach to estimate the performance of the proposed BS scheme by comparing the cumulative distribution function of a burst length in an OBS ingress node (source) with that in an egress node (destination) is introduced. A preemptive BS policy for different priority bursts is proposed to support the QoS of the OBS network. Finally, a simulation is given to validate the proposed analytical model in an existing OBS network with two priority bursts. It is shown that the proposed BS scheme can realize the service differentiation for multipriority traffic under the consideration of network topology-dependent parameters.

A simple frequency domain pilot interval allocation scheme is proposed for pilot-based channel estimation of a compatible single-sideband modulation direct detection optical orthogonal frequency division multiplexing transmission system. Compatible single-sideband modulation for orthogonal frequency-division multiplexing transmission with direct detection is strongly suggested to overcome chromatic dispersion without explicit dispersion compensation. The proposed optimal scheme can improve the channel estimation performance, by approximately three dB receiving sensitivity, without additional hardware or complex computation.

Recent progress on Si-based optical components for advanced optical communication systems has been demonstrated. The polarization beam splitter with extinction ratio of more than 20 dB and the optical 90-deg hybrid having phase deviation within ±5-deg were obtained using multimode interference structures. The 12  Gb/s modulators and the 20 GHz photodetectors were measured. Benefiting from the unique properties of silicon modulator, an error-free 80 Km transmission of the signals generated by our silicon carrier-depletion Mach-Zehnder modulator was also demonstrated at 10  Gb/s and the power penalty was as low as 1.15 dB. These results show that silicon photonics has a great potential in advanced optical communication systems.

Balloon-borne or ground-based high resolution long range observation has extensive applications in border monitoring and area surveillance. Performance of long-distance oblique or horizontal imaging systems is closely related to the atmospheric transmittance of the observing spectral band. Compared with visible and near infrared, the shortwave infrared (SWIR) band benefits from less scattering effects, which enables it to provide better quality images under harsh atmospheric conditions. We present a signal-to-noise ratio (SNR) model including atmospheric influences. Based on the model, image SNR was calculated in the spectral range of 0.4 μm to 2.5 μm. In order to validate the imaging performance model of SWIR, a multi-band camera was designed and spectral imaging experiments were conducted. The results clearly demonstrated the advantage of SWIR imaging. The experiments show that the contrast and SNR of SWIR images reduced insignificantly for long distances and under low visibility conditions. This advantage makes SWIR multiband cameras suitable for long-distance remote sensing and for observing through haze.

A real time multichannel dynamic erbium doped fiber amplifier (EDFA) Simulink model with flat gain and gain clamping facility has been developed on a MATLAB platform. We model the EDFA simulator with one-dimensional nonlinear differential equation that describes the time dependent population density. For the model to show gain flattening multiplexed channels at different wavelengths, the MATLAB function block is used. Next, to simulate the noise performance of EDFA. New forward amplified spontaneous emission (ASE) noise blocks are designed that add noise dynamically at signal wavelength. The model has been implemented in the study of performance characteristics of an EDFA in both C - and L -band signal amplification by simulation. Based on the designed ASE generator, noise figure for different signal wavelengths are calculated. For 980 nm pump power, the noise figure almost reaches the practical limit of 3 dB whereas for 1480 nm pump power, a variation of about 1.5 dB and 0.8 dB is observed from the practical limit for the C - and L -bands, respectively. The present model can be implemented successfully as a test bed in the study of EDFA gain dynamics over the entire third optical communication bandwidth (1525 to 1690 nm) in signal amplification.

We have developed an interferometer for gauge block calibration based on phase shifting algorithms. The measurement process can provide flatness, parallelism, and length. Wavelength values need to be corrected according to the refractive index of air. This correction is obtained indirectly using Edlén’s equation. High-resolution sensors provide the temperature, pressure, and relative humidity readings. To preserve stability, the interferometer is encapsulated in a chamber with active temperature control. Its design, measurement principle, calibration, stability, and reproducibility are analyzed. Since one goal is to employ robust and cheap diode lasers as light sources, we describe the system developed to stabilize a red laser diode using a mode locking technique with a reference gas cell. The instruments and assembly are used to avoid the Doppler effect in the gas cell, which would limit wavelength resolution. Several experiments are carried out to restrict the influence of environmental changes, which affect laser diode frequency.

The exposure schedule model for uniform diffraction efficiency is extended to be suitable for the partially overlapping multiplexing method. The proposed model is based on solving an optimization problem. Fifty holograms were multiplexed using the exposure schedule calculated with the extended model. The material used in the experiment is based on the photopolymerization of a free radical. By comparing the intensity of the reconstructed images during recording with that readout after recording, the calculated exposure schedule is verified to be effective to realize the uniform diffraction efficiency for the multiplexing holographic storage.

Energy conservation is an essential feature of optical waves propagating through refractive turbulence. It has been known for almost a quarter of a century that energy conservation has an important implication for the fluctuations in the images of the incoherent objects observed through turbulence, namely the image of the uniformly radiating area of an object does not scintillate. As a consequence, the low-contrast parts of an image exhibit weak fluctuation even for very strong turbulence, but scintillations near the sharp edges can be strong even for weak turbulence. The energy conservation property of the turbulent point spread function is essential for modeling turbulent image distortions, both for the development of the image processing techniques and for simulations of turbulent imaging. However, it is regularly overlooked in discussions of turbulent imaging theory and modeling in the current literature. We discuss the relations between energy conservation and anisoplanatism for the most common turbulence imaging models. Our analysis reveals that the only isoplanatic turbulent point spread function (PSF) that is compliant with energy conservation is the thin aperture plane phase screen. This implies that for near-the-ground imaging, and even for astronomical-type imaging under strong turbulence conditions, the turbulent PSF has to be modeled as a random function of four arguments with three functional constraints: non-negative values, finite bandwidth, and energy conservation.

Various atmospheric propagation effects are limiting the long-range performance of electro-optical imaging systems. These effects include absorption and scattering by molecules and aerosols, refraction due to vertical temperature gradients and scintillation and blurring due to turbulence. In maritime and coastal areas, ranges up to 25 km are relevant for detection and classification tasks on small targets (missiles, pirates). From November 2009 to October 2010 a measurement campaign was set-up over a range of more than 15 km in the False Bay in South Africa, where all of the propagation effects could be investigated quantitatively. The results have been used to provide statistical information on basic parameters as visibility, air-sea temperature difference, absolute humidity and wind speed. In addition various propagation models on aerosol particle size distribution, temperature profile, blur and scintillation under strong turbulence conditions could be validated. Examples of collected data and associated results are presented in this paper.

The recently proposed exponentiated Weibull (EW) fading channel model is assessed with partially coherent beams (PCBs) using the Gaussian Schell-model (GSM) theory. The use of a PCB in free-space optical links has been suggested as an atmospheric turbulence mitigation technique, called transmitter aperture averaging. A wave optics code based on the GSM theory is used to generate a PCB propagating in atmospheric turbulence, and the probability distribution function (PDF) is obtained from the simulated irradiance data. This study on the PDF includes the new proposed EW model in the presence of aperture averaging, in weak-to-strong turbulence regime. Point receiver conditions are also analyzed. For completeness of the study, the Lognormal and the Gamma-Gamma models have also been included in the analysis, allowing for a direct comparison to the EW distribution. Using a least-squares curve fitting algorithm, the EW model always has the best fit to simulated PDF data. Thus, the EW fading channel model proves to be valid for PCBs.

An aerosol modulation transfer function (MTF) model is developed to assess the impact of aerosol scattering on passive long-range imaging sensors. The methodology extends from previous work to explicitly address imaging scenarios with a nonuniform distribution of scattering characteristics over the propagation path and incorporates the moderate resolution transfer code database of aerosol cross-section and phase function characteristics in order to provide an empirical foundation for realistic quantitative MTF assessments. The resulting model is compared with both predictions from a Monte-Carlo scattering simulation and a scene-derived MTF estimate from an empirical image, with reasonable agreement in both cases. Application to long-range imaging situations at both visible and infrared wavelengths indicates that the magnitude and functional form of the aerosol MTF differ significantly from other contributors to the composite system MTF. Furthermore, the image-quality impact is largely radiometric in the sense that the contrast reduction is approximately independent of spatial frequency, and image blur is practically negligible.

An algorithm for the fusion of data used for target search and tracking originated by a bidimensional radar and infrared search and track is proposed and described. To permit a fusion process between two systems whose measurements are not completely comparable, a new strategy for mixing the system states is introduced, thus obtaining a set of homogeneous measurements. We describe the rationale behind the method and develop mathematical aspects necessary to obtain the equation for the fusion of tracking data. An analysis of the estimation errors associated with the proposed model is also described. Some simulation results demonstrate the capabilities of the presented technique.

Target range estimation is traditionally based on radar and active sonar systems in modern combat systems. However, jamming signals tremendously degrade the performance of such active sensor devices. We introduce a simple target range estimation method and the fundamental limits of the proposed method based on the atmosphere propagation model. Since passive infrared (IR) sensors measure IR signals radiating from objects in different wavelengths, this method has robustness against electromagnetic jamming. The measured target radiance of each wavelength at the IR sensor depends on the emissive properties of target material and various attenuation factors (i.e., the distance between sensor and target and atmosphere environment parameters). MODTRAN is a tool that models atmospheric propagation of electromagnetic radiation. Based on the results from MODTRAN and atmosphere propagation-based modeling, the target range can be estimated. To analyze the proposed method’s performance statistically, we use maximum likelihood estimation (MLE) and evaluate the Cramer-Rao lower bound (CRLB) via the probability density function of measured radiance. We also compare CRLB and the variance of MLE using Monte-Carlo simulation.

We present the use of polyacrylate membranes for the fabrication of pneumatically actuated variable lenses. Whereas the most commonly used membrane material for tunable liquid-filled lenses is polydimethylsiloxane (PDMS), polyacrylate membranes have the advantages of high resistance to swelling in silicone oil and enhanced compatibility with a wide range of aqueous optical liquids. These features are quantitatively demonstrated by comparing the material properties and performance of PDMS and polyacrylate membrane lenses. The optical transparency of polyacrylate is more than 92%. The surface roughness is below 3.3 nm rms, and reversible elastic deformation could be demonstrated. Optical measurements show that the cutoff frequency of the modulation transfer function of polyacrylate lenses with different liquid fillings, using a reference contrast of 0.2, is more than 1.5 times larger than that of the same system assembled with PDMS membranes filled with water.

For the purpose of biometric person identification, iris recognition uses the unique characteristics of the patterns of the iris; that is, the eye region between the pupil and the sclera. When obtaining an iris image, the iris’s image is frequently rotated because of the user’s head roll toward the left or right shoulder. As the rotation of the iris image leads to circular shifting of the iris features, the accuracy of iris recognition is degraded. To solve this problem, conventional iris recognition methods use shifting of the iris feature codes to perform the matching. However, this increases the computational complexity and level of false acceptance error. To solve these problems, we propose a novel iris recognition method based on multi-unit iris images. Our method is novel in the following five ways compared with previous methods. First, to detect both eyes, we use Adaboost and a rapid eye detector (RED) based on the iris shape feature and integral imaging. Both eyes are detected using RED in the approximate candidate region that consists of the binocular region, which is determined by the Adaboost detector. Second, we classify the detected eyes into the left and right eyes, because the iris patterns in the left and right eyes in the same person are different, and they are therefore considered as different classes. We can improve the accuracy of iris recognition using this pre-classification of the left and right eyes. Third, by measuring the angle of head roll using the two center positions of the left and right pupils, detected by two circular edge detectors, we obtain the information of the iris rotation angle. Fourth, in order to reduce the error and processing time of iris recognition, adaptive bit-shifting based on the measured iris rotation angle is used in feature matching. Fifth, the recognition accuracy is enhanced by the score fusion of the left and right irises. Experimental results on the iris open database of low-resolution images showed that the averaged equal error rate of iris recognition using the proposed method was 4.3006%, which is lower than that of other methods.

People tracking in crowded scenes from closed-circuit television (CCTV) footage has been a popular and challenging task in computer vision. Due to the limited spatial resolution in the CCTV footage, the color of people’s dress may offer an alternative feature for their recognition and tracking. However, there are many factors, such as variable illumination conditions, viewing angles, and camera calibration, that may induce illusive modification of intrinsic color signatures of the target. Our objective is to recognize and track targets in multiple camera views using color as the detection feature, and to understand if a color constancy (CC) approach may help to reduce these color illusions due to illumination and camera artifacts and thereby improve target recognition performance. We have tested a number of CC algorithms using various color descriptors to assess the efficiency of target recognition from a real multicamera Imagery Library for Intelligent Detection Systems (i-LIDS) data set. Various classifiers have been used for target detection, and the figure of merit to assess the efficiency of target recognition is achieved through the area under the receiver operating characteristics (AUROC). We have proposed two modifications of luminance-based CC algorithms: one with a color transfer mechanism and the other using a pixel-wise sigmoid function for an adaptive dynamic range compression, a method termed enhanced luminance reflectance CC (ELRCC). We found that both algorithms improve the efficiency of target recognitions substantially better than that of the raw data without CC treatment, and in some cases the ELRCC improves target tracking by over 100% within the AUROC assessment metric. The performance of the ELRCC has been assessed over 10 selected targets from three different camera views of the i-LIDS footage, and the averaged target recognition efficiency over all these targets is found to be improved by about 54% in AUROC after the data are processed by the proposed ELRCC algorithm. This amount of improvement represents a reduction of probability of false alarm by about a factor of 5 at the probability of detection of 0.5. Our study concerns mainly the detection of colored targets; and issues for the recognition of white or gray targets will be addressed in a forthcoming study.

A novel approach for automated road network extraction from multispectral WorldView-2 imagery using a knowledge-based system is presented. This approach uses a multispectral flood-fill technique to extract asphalt pixels from satellite images; it follows by identifying prominent curvilinear structures using template matching. The extracted curvilinear structures provide an initial estimate of the road network, which is refined by the knowledge-based system. This system breaks the curvilinear structures into small segments and then groups them using a set of well-defined rules; a saliency check is then performed to prune the road segments. As a final step, these segments, carrying road width and orientation information, can be reconstructed to generate a proper road map. The approach is shown to perform well with various urban and suburban scenes. It can also be deployed to extract the road network in large-scale scenes.

A system is proposed for automatic reading of the number of dots on dice in general table game settings. Different from previous dice recognition systems that recognize dice of a specific color using a single top-view camera in an enclosure with controlled settings, the proposed one uses multiple cameras to recognize dice of various colors and under uncontrolled conditions. It is composed of three modules. Module-1 locates the dice using the gradient-conditioned color segmentation, proposed, to segment dice of arbitrary colors from the background. Module-2 exploits the local invariant features good for building homographies, giving a solution to segment the top faces of the dice. To identify the dots on the segmented top faces, a maximally stable extremal region detector is embedded in module-3 for its consistency in locating the dot region. Experiments show that the proposed system performs satisfactorily in various test conditions.

An advanced two-step motion estimation algorithm that uses adjustable partial distortion for fast motion estimation is proposed. To overcome the demerits of existing two-step search algorithms, we propose a new, fast two-step algorithm, which achieves both speed and peak signal-to-noise ratio (PSNR) improvement by adding two predicted points. We improve the two-step search by using the relationship between a neighbor block and the current block. The proposed algorithm is 187 times faster than full search and 2.7 times faster than two-step edge based A partial distance search with negligible PSNR degradation. Therefore it is suitable for real-time video implementation.

We present a new method for converting circularly polarized light into radially or azimuthally polarized light by using an achromatic meniscus axicon and two additional halfwave retarders. The rotationally symmetric meniscus axicon, consisting of a pair of convex and concave conical surfaces with the same apex angle, exploits the double total internal reflections when light passes through it to produce π/2 phase retardation with an azimuth-variant polarization orientation. The properties of highly achromatic retardation, which provide excellent stability of retardation against temperature variation for the meniscus axicon, is numerically demonstrated.

We propose an approach to control the polarization and intensity of the focusing field with multiple focal spots in a high-numerical-aperture imaging system. This focused field is explained as the reversal radiation of the dipole array with presupposed oscillating direction in the focal volume. By engineering the structure of the electric dipole array and reversing the radiation from this dipole array, the local manipulation of intensity and polarization in the focal region is achieved, and the required field at the pupil plane is derived. A focusing field with six vectorial focal spots is created as an example to verify this method. This multifocal field will meet potential application in polarization-dependent optical microscope and optical trapping for multiple particles.

We present a hybrid configuration of joint transform correlator (JTC) and joint fractional transform correlator (JFTC) for encryption purpose. The original input is encoded in the joint fractional power spectrum distribution of JFTC. In our experimental arrangement, an additional random phase mask (master key) is holographically generated beforehand by a Mach–Zehnder interferometer with a JTC as the object arm. The fractional order of JFTC, together with the master key, can remarkably strengthen the safety level of encryption. Different from many previous digital-holography-based encryption schemes, the stability and alignment requirement for our system is not high, since the interferometric operation is only performed in the generation procedure of the master key. The advantages and feasibility of the proposed scheme have been verified by the experimental results. By combining with a multiplex technique, an application for multiple images encryption using the system is also given a detailed description.

We have designed and constructed a transverse excitation atmospheric-pressure CO ₂ laser using a multipass configuration. We compare the measured results of both laser output power and energy from various modes of operation. We have measured the maximum laser output energy to be 19 J and the peak output power to be greater than 100 MW.