This PDF file contains the editorial “Editorial” for OE Vol. 43 Issue 03

Various atmospheric properties can impact sensor performance modeling. Transmission, visibility, and contrast can be used in relatively simple expressions to summarize the impact of the atmosphere on static images. Transmission and contrast can be used together in an expression called the sky-to-ground ratio. Experimental measurements of radiance and imagery are used to assess the applicability of the delta Eddington radiative transfer approximation for estimation of apparent contrast and sky-to-ground ratio. The experiments were performed in southern New Mexico near the autumnal equinox. Delta Eddington calculations are made for two types of aerosol phase functions: Henyey-Greenstein and Deirmendjian haze. Comparisons also include computations from a much simpler radiative transfer model, the Huschke model. These experiments support the use of a relatively simple contrast model that more accurately reflects nature than more empirical models.

Effects of humid aerosols and fog on optical wave propagation at 1.064 µm over various horizontal atmospheric communication links are investigated both experimentally and theoretically by use of theoretical and empirical models as best fits of experimental data. Mie scattering is used to describe the attenuation of optical waves by aerosols for lower elevation horizontal atmospheric links. The geometrical optics approximation is used to obtain the extinction coefficient for optical waves at 1.064 µm passing through clouds, fog, water droplets, and atmospheric particles with dimensions larger than the wavelength. Good agreement between a new model of propagation effects through such particles, and measurements carried out at two different sites in southern and northen Israel, is obtained.

It is now possible to design real-time, low-cost computer vision systems even in personal computers due to the recent advances in electronics and the computer industry. Due to this reason, it is feasible to develop computer-vision-based human-computer interaction systems. A vision-based continuous GraffitiTM-like text entry system is presented. The user sketches characters in a GraffitiTM-like alphabet in a continuous manner on a flat surface using a laser pointer. The beam of the laser pointer is tracked on the image sequences captured by a camera, and the corresponding written word is recognized from the extracted trace of the laser beam.

We have recently observed several features from a randomly rough dielectric film on a reflecting metal substrate including a change in the spectrum of light at the satellite peaks, the high-order correlation, and enhanced backscattering from the grazing angle. In this paper, we focus on the enhanced backscattering phenomena. The backscattering signal at small grazing angles is very important for vehicle re-entrance and subsurface radar sensing applications. Recently, we performed an experimental study of far-field scattering at small grazing angles, especially enhanced backscattering at grazing angles. For a randomly weak, rough dielectric film on a reflecting metal substrate, a much larger enhanced backscattering peak is measured. Experimental results are compared with theoretical predictions based on a two-scale surface roughness scattering model.

Hollow waveguides are made from square and rectangular glass tubing for the transmission of polarized CO₂ laser radiation. These hollow noncircular cross section glass waveguides have Ag and AgI thin film coatings deposited on the inside surface using liquid-phase chemistry techniques. The losses for straight square (500×500 µm) and rectangular (225×1250 µm) hollow glass waveguides at 10.6 µm were 0.8 and 2.2 dB/m, respectively. The degree of polarization is more than 90% for the rectangular waveguides, and this degree of polarization is preserved when rectangular guides are bent or twisted to rotate the polarization.

We propose a new speckle method for enhancing the anticounterfeiting ability of holograms. The method adds light-diffusion marks on holograms. These marks are constituted with periodic speckle patterns. The size of element patterns is very small, so a microscope must be used to check the 2-D microstructure of a mark. When a laser beam illuminates a light-diffusion mark, the diffused light produces a special matrix intensity distribution. Because it is difficult to create an identical random speckle arrangement using different process setups, the matrix intensity distribution diffracted from a specially created light-diffusion mark is nearly impossible to counterfeit. Although holographic films possess birefringent phenomena, the diffraction efficiencies of marks that fit some confinement conditions can be kept stable for light with different polarizations. The proposed method is a good choice for enhancing hologram anticounterfeiting characteristics.

Robustness to noise and/or illumination variations has been a major issue with change detection. We present a novel change detection scheme that is robust to both noise and illumination changes. The major difference of our method compared to the existing ones is that our algorithm globally estimates and compensates for the illumination changes between two input images, whereas the previous approaches rely on some local change metrics for illumination-independent detection. Specifically, a piecewise quadratic model for describing global illumination changes (GICs) is formulated, and an efficient estimation algorithm for the model parameters is proposed. In this way, we can successfully detect any types of local changes, whereas the previous approaches show either limited performances in detecting object interiors or severe performance degradations when global illumination changes occur. We also present a noise-adaptive thresholding method for the GIC-compensated intensity differences. The noise variance is estimated accurately based on symmetricity and decrease of zero-mean noise distributions, and then the decision threshold is selected adaptively to the estimated variance. Experimental results show that the proposed method is very robust to both noise and illumination changes, and outperforms the previous algorithms in various aspects.

In modern traffic surveillance, computer vision methods have often been employed to detect vehicles of interest because of the rich information content contained in an image. Segmentation of moving vehicles using image processing and analysis algorithms has been an important research topic in the past decade. However, segmentation results are strongly affected by two issues: moving cast shadows and reflective regions, both of which reduce accuracy and require postprocessing to alleviate the degradation. We propose an efficient and highly accurate texture-based method for extracting the boundary of vehicles from the stationary background that is free from the effect of moving cast shadows and reflective regions. The segmentation method utilizes the differences in textural property between the road, vehicle cast shadow, reflection on the vehicle, and the vehicle itself, rather than just the intensity differences between them. By further combining the luminance and chrominance properties into an OR map, a number of foreground vehicle masks are constructed through a series of morphological operations, where each mask describes the outline of a moving vehicle. The proposed method has been tested on real-world traffic image sequences and achieved an average error rate of 3.44% for 50 tested vehicle images.

The block-matching motion estimation algorithm using a translational motion model cannot provide acceptable image quality in low bit-rate coding. To improve coding performance, we can use image warping using affine transformation as a more complicated motion model than the translational motion model. However, when some node points are flipped over in the image warping method, it creates severe deformations of the mesh structure and brings image degradations. It also requires large computational complexity. We show that wide search ranges do not always improve reconstructed image quality due to the large deformation of meshes. We analyze optimal search ranges according to frame difference and decide variable search ranges adaptively to get a motion vector at each node point. Since the block with a larger error than a threshold makes a large distortion, we give higher priority during motion estimation at a certain rate. To reduce computational complexity, we also introduce an adaptive partial matching method instead of applying the hexagonal matching method on the whole image. As a result, we develop an effective image warping method in terms of computational complexity, reasonable reconstructed image quality, and fewer number of coding bits.

We show an embedded wavelet coder with a prioritization protocol, which provides an acceleration of benefit gain for quantizers of interest at extremely low bit rates. This means that decoded outputs provide better image quality at very low bit rates. By changing its risk attitude within a rational approach, which avoids certain forms of behavioral inconsistency, a quantifier may modify the gain in benefit that results from a particular bitstream candidate to be transmitted at a truncation time. At medium and high bit rates, quantizers exhibit only low risk tolerance, since they are aware that the next truncation time might be the last one. Since at extremely low bit rates the target bit rate may be far away, quantizers are able to exhibit higher risk tolerance, and as a consequence they will have greater possibilities of accelerating their benefit gain. The cooperation among subsets of the quantizers may be needed to increase the risk tolerance at very low bit rates within a rational approach and still prioritize first the more relevant pieces of information at each truncation time. The members of any coalition of quantizers can then negotiate a feasible change in the risk attitudes of the quantizers of the coalition that would benefit them all. The final risk tolerance of different quantizers comes from the balance of power among the coalitions of quantizers. The prioritization protocol chooses to transmit, at each truncation time, a bitstream for the quantizer that receives the highest payment (per coding bit) in a coalitional game, which minimizes the dissatisfaction of coalitions.

Earlier techniques used for noise filtering were global filters based on the assumption of a stationary image model. Although the stationarity assumption enables the use of the Fast Fourier transform (FFT)-based algorithm, such filters tend to oversmooth edges where stationarity is not satisfied. Recently, various noise smoothing algorithms based on the nonstationary image model have been proposed to overcome this problem. In most conventional nonstationary image models, however, pixels are assumed to be uncorrelated to each other in order not to increase a computational burden too much. As a result, some detailed information is lost in the filtered results. We propose a computationally feasible adaptive noise smoothing algorithm that considers the nonstationary correlation characteristics of images. We assume that an image has a nonstationary mean and can be segmented into subimages that have individually different stationary correlations. Taking advantage of the special structure of the covariance matrix that results from the proposed image model, we derive a computationally efficient FFT-based adaptive linear minimum mean-square-error filter for cases of signal uncorrelated additive, multiplicative, and film-grain noises. The justification for the proposed image model is presented, and the effectiveness of the proposed algorithm is demonstrated experimentally.

In a previous work, a new method was introduced for correlation matching of binary targets (e.g., a light, uniform target on a dark, uniform background). This new method was based on the use of an augmented search template that contains not only the occupied pixel fractions of the synthetic reference that is being located, but also the derivatives of these pixel fractions with respect to shifts of the template along the image axes. In the present work, the augmented template technique is extended to cases in which a binary target is used for image registration, but is not rendered as a binary image feature due to experimental artifacts such as specular reflection, mixed image contrast, or partial occlusion. It is shown that subpixel localization of the target can still be accomplished, by extending the concept of a single augmented template to a composite one, which consists of overlapping three-by-three subtemplates. Examples of noncomposite and composite augmented template matching are demonstrated experimentally.

Infrared images often present distortions induced by the measurement system. Image processing is thus an essential part of infrared measurements. A distortion model based on a convolution product is presented. The analytical form of the convolution kernel has been obtained from an image formation theory, along with an analysis of the sampling of the focal plane array camera detector's matrix. Image restoration is an ill-posed problem, and its solution can be obtained using regularization methods. In this work, image restoration is performed using a variation of Tikhonov regularization that makes use of the particular form of the convolution kernel matrix, which is built as a block-circulant matrix that admits a diagonal form in the 2-D Fourier space. The restoration procedure is used to restore a knife-edge infrared source image.

An optoelectronic integrated circuit (OEIC), consisting of a photodiode for wavelengths up to 850 nm and a transimpedance amplifier, is introduced together with a voltage-up-converter to reduce the response time of the photodiode by increasing its reverse voltage. Depending on the stage count of the Dickson-type voltage converter, the bandwidth can be increased by factors of 10 to 30. This improvement is due to the elimination of slow carrier diffusion in the photodiode. Bandwidth, rise and fall times, eye diagram, as well as voltage converter characteristics are given for OEICs realized in a 0.6-µm bipolar CMOS (BiCMOS) process.

The design and fabrication of a 4×4 multimode interference (MMI) coupler is reported. A photopatternable organic-inorganic sol-gel on silica-on-silicon is adopted for the device fabrication. Optimization of waveguide parameters led to the coupler excess loss below 1 dB and power imbalance below 0.2 dB. An optical 90-deg hybrid based on the coupler is realized and tested. The experimental data are in very good agreement with predicted simulation results, demonstrating the simplicity and exactness of the sol-gel method as an advantageous fabrication route in integrated optics.

Quantum wire lasers and modulators offer superior performance over their quantum well counterparts. We present simulations of an integrated InGaAs-InP quantum wire laser-modulator structure operating at 1.55 µm. In the case of quantum wire lasers, we have computed the optical gain as a function of current density for wires having widths ranging between 60 and 100 Å. For example, the threshold current density of 61 A/cm2 is computed for a wire with a width of 80 Å. In the case of quantum wire modulators, we compute the changes in the absorption coefficient and index of refraction due to an external electric field to implement electroabsorptive and electrorefractive optical modulators. For example, the absorption coefficient changes (Δα/α) by 450% when an applied electric field changes from 30 to 60 kV/cm for an 80 Å quantum wire. The corresponding change of refractive index is about 11%. A structure integrating an edge-emitting laser with an in-line type electroabsorptive or electrorefractive modulator is presented. The quantum wires are designed to operate the laser at a wavelength that corresponds to the Stark effect tuning of the modulator. We can maximize the changes in electroabsorptive and electrorefractive modulators by choosing the right combination of wire dimensions, operating wavelengths, and electric fields.

An integrated Mach-Zehnder interferometer made of electro-optic (EO) polymers with a dimension of 3×1.2 cm was fabricated as a wideband rf receive antenna. When an electric field is applied to the interferometer arm(s) made of EO material, a phase delay is generated that results in a net imbalance in the interferometer, and thus a change in the output intensity. This output intensity change, which contains electric field strength and temporal profile information, is then read by a photodetector and processed. This antenna was tested in a µ-strip traveling wave electromagnetic cell at frequencies from 100 MHz to 1.04 GHz. The test results show the antenna had a good linear response over a 70-dB power range. The lowest possible measured E_min was about 4 mV/m (or 2.1 pW/cm²) at 1-kHz resolution bandwidth with a laser power of 0.4 mW (–4 dBm) measured after the sensor. The measured E-field signal increases with increasing laser power, which indicates that significant sensitivity improvement can be easily obtained by lowering passive losses. The antenna sensitivity can be further improved by lowering the device insertion loss, optimizing the photodetector and detection circuitry, and using EO polymers with higher EO coefficients.

We propose a sinusoidal phase-modulating laser diode interferometer that uses a charge-coupled device (CCD)-based additive operation on four integrating buckets. By shifting the injection-current bias of a laser diode to introduce additional phase shifts, a portion of the subtractive operations on the integrating buckets become additive operations, which are achieved in the CCD. This approach serves to reduce both data processing and measurement time.

We discuss some properties and limitations of the method called fringe compensation in electronic speckle pattern interferometry (ESPI), or TV holography, based on fringe visibility data. The properties of phase maps used in this method and their impact on the process is discussed, then experimental result are presented that apply the method to rigid body rotation measurements, producing simple parallel fringes in two different cases.

High-frequency fringe patterns found in non-null interferometric testing of aspheres require the use of special detector arrays containing small, widely spaced pixels. A sparse array camera with the ability to detect high spatial frequencies has been developed. The modulation transfer function (MTF) of the camera is measured using a sinusoidal fringe pattern generated by a Mach-Zehnder interferometer. Spatial frequencies up to 400 cycles/mm are generated and used to characterize the MTF of the camera.

Null correctors are important in the fabrication of aspheric optics. Although null correctors simplify testing of aspheric surfaces, they can increase the risk of fabricating aspheric surfaces. Undetected errors in the null corrector will result in an aspheric surface that does not meet design specifications. To prevent such problems, a null corrector is certified prior to using it to test an aspheric surface during fabrication. Certification verifies that the null corrector has been produced properly. Current methods of certification that include computer-generated holograms and diamond-turned mirrors require a mathematical description of the certifier. We provide sag and phase formulas for describing such certifiers. The formulas can be used to define certifiers for a broad range of aspheric surfaces. For each aspheric test surface, the specific certifier parameters are found through optimization using default merit functions. Via two different aspheric surfaces, we demonstrate the usefulness and simplicity of our truncated-series sag and phase formulas to define certifiers.

A new wavelength multiplexing configuration for self-referenced fiber optic intensity sensors using fiber Bragg gratings and wavelength division multiplexing (WDM) couplers is investigated. First, the network multiplexing concept is characterized, and then the self-referenced intensity sensor is presented, which is the basis of each individual sensor in the network. The implemented experimental setup of the multiplexing network is described, and results are presented considering the crosstalk, resolution, and power budget of the sensing multiplexing network. The characteristics and features of the configuration proposed are addressed.

A new method for both the phase-height mapping and the 3-D coordinate calibration in phase-measuring profilometry (PMP) is presented. A calibration gauge containing four virtual calibration planes is designed. The application of the calibration gauge avoids the translation of the standard plane during the calibration process. Furthermore, circular steps are designed to calibrate lateral coordinates automatically. With this calibration gauge, both the phase-height mapping and lateral coordinates calibration could be done simultaneously through only one measurement. Additionally, to recover a continuous phase distribution of all the steps with the same height, an iterative procedure is proposed. The effectiveness of the proposed method is demonstrated by experimental results.

A multispectra method is proposed for the error reduction of the quantized Fourier modulus in the iterative Fourier transform algorithms used for phase retrieval. The Fourier modulus is usually obtained by measuring the Fourier intensity with a digital device, thus the quantization error caused in the measurements of Fourier intensity leads to the error of the reconstructed object when iterative Fourier transform algorithms are used. The idea of the multispectra method uses several Fourier intensity distributions for various measuring ranges to generate a Fourier intensity distribution with low-quantization error. The error reduction of Fourier intensity with the multispectra method connects to the improvement of the phase retrieval with the iterative Fourier transform algorithms. Simulations are performed to demonstrate the effect of the multispectra method for phase retrieval with the iterative hybrid input-output algorithm.

We study the possibility of introducing programmable filters in the Fourier plane of an optical free-space wavelength demultiplexer to provide wavelength-band selection or programmable optical add and drop multiplexing. Various 4f configurations are modeled, and we compare the respective advantage of two main cases: the first where the dispersive element is superimposed in the Fourier plane with a programmable transmittance, the second where the dispersive element is combined with the lens(es) and the Fourier plane is free to set the programmable element. An analytical model of the beam propagation is proposed in the case of a Gaussian beam to make easier the choice of adjustable parameters and optical configurations. The potential use of the Fourier plane free configurations is assessed in terms of wavelength-band resolution, selectivity, and attenuation dynamic range.

Red light can convert a blue membrane into a pink membrane, which has good thermal stability and can be converted back by illumination of blue light. Taking advantage of this property, a reusable biological film based on a deionized blue membrane is demonstrated, which can be used to store and erase images conveniently. The device exhibits a resolution of ~64 line pairs/mm. The modulation transfer function (MTF) of the blue membrane system is presented.

Salinity measurement with a reflex optical and electrical dual-differential sensor is experimentally developed. The sensor exploits the beam deviation due to optical refraction at the receiving endface of the measurement cell, which is caused by changes in the refractive index with different concentrations of saltwater. With the help of a right-angle reflecting prism and in the presence of a referenced distilled water cell with an inclined optical window, optical differential measurement of incident beam deviations is implemented, and the deviation caused by changes in salinity are detected by a position-sensitive detector (PSD) with an electrical differential signal processing technique. Experimental setup and measurement principles are discussed. Salinity measurements based on this method avoid the influences by light power fluctuation of the incident light and temperature drift. Experimental results indicate that the estimated salinity measurement resolution can reach 0.012%.

A laser beam is used to determine the radius of curvature of a material surface. For this, an equation relating the radius of curvature of a material surface to the curvature of a laser wavefront and the spot radius of a laser beam, and the optical path length, is first established. Then, by substituting the calculated radius of the wavefront curvature at the sample, the measured spot radius of the beam at the sample, and at the testing plane in the equation, the radius of curvature of the sample surface can be determined. Furthermore, the optical-lever method to determine the surface's curvature has practical application. A comparison between results obtained with the proposed and optical-lever methods is made. The two sets of values yield the radii of surface curvature that are in good agreement. But if the experimental layout, signal detection, and measuring capability are also compared, the proposed method is superior to the optical-lever method.

The surface topography of thin, transparent materials is of interest in many areas. Some examples include glass substrates for computer hard disks, photomasks in the semiconductor industry, flat panel displays, and x-ray telescope optics. Some of these applications require individual foils to be manufactured with figure errors that are a small fraction of a micron over 10- to 200-mm lengths. Accurate surface metrology is essential to confirm the efficacy of manufacturing and substrate flattening processes. Assembly of these floppy optics is also facilitated by such a metrology tool. We report on the design and performance of a novel deep-ultraviolet (deep-UV) Shack-Hartmann surface metrology tool developed for this purpose. The use of deep-UV wavelengths is particularly advantageous for studying transparent substrates such as glass, which are virtually opaque to wavelengths below 260 nm. The system has a 143×143-mm² field of view at the object plane. Performance specifications include 350-µrad angular dynamic range and 0.5-µrad angular sensitivity. Surface maps over a 100 mm diam are accurate to <17-nm rms and repeatable to 5 nm rms.

We have developed a novel target set to scale our underwater lidar imaging (UWLI) video system in a 3-m tank with turbid water (1.0/m). By use of light speed in water 22.5 cm/ns, the set consists of a series of three bar targets at 22.5-cm intervals along the laser illumination direction, but distributed over the section across. As a result, a sequence of nice gated images (video), in steps of 1-ns delay time, are presented, which give very clear revelation of "sliced-view" phenomenon for nanosecond-level range gating in such a limited water body. Also, the depth of gating (DOG) and DOG profile of the UWLI system are measured for the first time, which are used for evaluating the gating performance efficiently.

A six-wavelength hybrid dense-wavelength-division-multiplexing (DWDM) system with CATV, 256-QAM, and OC-48 (2.5 Gb/s) video and digital trunking applications, which employ optical vestigial sideband (VSB) filters to improve system performances, are proposed and demonstrated. Excellent performances of composite second order (CSO) and composite triple beat (CTB) are obtained, accompanied by acceptable carrier-to-noise ratio (CNR) value for CATV. Low bit error rate (BER) is also achieved for the 256-QAM and OC-48 digital channels in our proposed system.

A hybrid wavelength-division-multiplexing (WDM) system based on a broadband amplified spontaneous emission (ASE) optical source for CATV, 256-QAM, and OC-48 transport is proposed and demonstrated. The proposed hybrid WDM system uses four spectrum-sliced wavelengths to transmit 111 AM-VSB channels, 4 256-QAM digital passband channels, and 1 OC-48 digital baseband channel simultaneously. Since our proposed system does not use multiple distributed feedback (DFB) laser diodes, it reveals a prominent one with simpler and more economic advantages than that of traditional hybrid WDM systems.