This PDF file contains the editorial “Research in the Face of Terror” for OE Vol. 45 Issue 09

Unselective regrowth for fabricating 1.5-µm InGaAsP multiple-quantum well (MQW) distributed-feedback (DFB) buried heterostructure (BH) lasers is developed. The experimental results exhibit superior characteristics, such as a low threshold of 8.5 mA, high slope efficiency of 0.55 mW/mA, circular-like far-field patterns, the narrow linewidth of 2.5 MHz, etc. The high performance of the devices effectively proves the feasibility of the new method to fabricate buried heterostructure lasers.

The aim of the present work is to propose a brand-new algorithm based on an adaptive double threshold nonlinear anisotropic diffusion equation (DTPDE) to detect and track moving dim targets against complex cluttered background in infrared (IR) image sequences. We also illustrate the performance comparisons of the proposed algorithm DTPDE and two-dimensional least mean squares (TDLMS) on real IR image sequence data. Extensive experiment results demonstrate the proposed novel algorithm's flexibility and adaptability in detecting moving weak dim targets.

We investigate the appearance manifold of different face poses using manifold learning. The pose estimation problem is, however, exacerbated by changes in illumination, spatial scale, etc. In addition, manifold learning has some disadvantages. First, the discriminant ability of the low-dimensional subspaces obtained by manifold learning often is lower than traditional dimesionality reduction approaches. Second, manifold learning methods fail to remove the redundancy, such as high-order correlation, among original feature vectors. In this work, we propose a novel approach to address these problems. First, face images are transformed by Gabor filters to obtain a set of overcompleted feature vectors, which can remove intrinsic redundancies within images and provide orientation-selective properties to enhance differences among face poses as well. Second, supervised locality preserving projections (SLPPs) are proposed to reduce dimensionality and obtain the low-dimensional subspace, which has the ability to maximize between-class distance and minimize within-class distance. Finally, the support vector machine (SVM) classifier is applied to estimate face poses. The experimental results show that the proposed approach is effective and efficient.

Integral field spectroscopy (IFS) provides a spectrum simultaneously for each spatial sample of an extended 2-D field. It consists of an integral field unit (IFU), which slices and rearranges the initial field along the entrance slit of a spectrograph. We present an original design of IFU based on the advanced image slicer concept. To reduce optical aberrations, pupil and slit mirrors are disposed in a fan-shaped configuration, which means that angles between incident and reflected beams on each element are minimized. The fan-shaped image slicer improves image quality in terms of wavefront error by a factor of 2 compared with a classical image slicer, and furthermore, it guaranties a negligible level of differential aberration in the field. As an example, we present the design LAM used for its proposal at the near-infrared spectrograph (NIRSpec/IFU) invitation of tender for the James Webb Space Telescope (JWST).

High-resolution, large-angle optical beam scanning methods are sought to meet the ever-increasing demands of free-space laser communication, medical imaging and treatment, printers, scanners, and laser radar. We present a precise steering method with high angular resolution and a wide scanning range. The proposed beam-steering device is also lightweight and compact, which are significant advantages in many applications. The scanning is implemented by means of a pair of diffraction gratings, which can be translated relative to one another, and a tunable-wavelength laser. Thus the beam is steered by the combined effect of two independent mechanisms. The agility of wavelength tuning enhances the performance of a grating-based device, while the sensitivity to chromatic aberrations is minimized by performing the coarse steering with the diffraction grating. The system performance is demonstrated experimentally, and the results are reported. To the best knowledge of the authors, We present for the first time a scanning system that includes a combination of a pair of diffraction gratings and a tunable-wavelength laser.

Camera calibration is an important procedure for the image-based three-dimensional (3D) shape reconstruction of existing objects. Methods that use different mathematics for the computation of the camera calibration have been reported in the literature. But a reliable detection of calibration patterns is not considered in these methods, which prevents their practical use. A robust recognition method for the detection of a checkerboard pattern for camera calibration is proposed. After introduction of the principle of this method, experiments are used to check the method on a wide range of real data. The results show that the method is robust over a range of illumination and a complicated background. The proposed method can be used for automatic camera calibration in real-world environments.

The presence of a beam combination system that forms a united image in a common focal plane is one of the features of systems with an optical sparse array. Any control system of a beam combiner has a limited accuracy and, as a result, introduces some optical errors that influence the quality of the united image. This especially concerns systems with a dynamic aperture reconfiguration during an active process of observation. We present analytical expressions for the instantaneous spectral optical transfer function (OTF) of the optical sparse array consisting of N circular and annular subapertures depending on the residual random image alignment and optical path difference errors, and the average OTF for the Gaussian probability distributions depending on the statistical parameters of the last. The formulas are deduced on the basis of the Fraunhofer approach to the Kirchhoff diffraction theory. The results can be used for both space and earth sciences applications.

An instrument for measuring the level of a liquid surface is described. The device is compact, requires no special handling, is noncontact, and can measure variations in level of the order of a micrometer, although this value can be suitably modified by changing the setup parameters. The instrument was developed as a machine flatness profilometer using the liquid level as a reference surface. Two applications of the instrument as a machine profilometer are presented, the first in order to measure the straightness of the displacement of the spindle of a polishing machine and the second in order to find the flatness error of a coordinate-measuring machine of large dimensions.

A method for three-dimensional (3D) displacement measurement by separating out-of-plane displacement from in-plane displacement is presented. A reference beam is added to a dual-beam symmetric illumination electronic speckle pattern interferometry (ESPI) system and shared by the two illuminations. The test object is illuminated by the two object beams, respectively. Two phase maps, which include out-of-plane and in-plane displacement, can be obtained by phase-shifting techniques. In order to decrease electronic noises in the phase maps, one of the phase maps is calculated by the reversed phase-shifting method presented. By using inverse phase distribution, out-of-plane displacement can be easily separated from in-plane displacement by subtraction and can greatly decrease electronic noises. The principle of the method is presented and proved by a typical three-point bending experiment. Experimental results are offered.

Spectroscopic data recorded by dispersion spectrophotometers is usually degraded by the response function of the instrument. Double- or triple-cascade spectrophotometers use narrow slits to improve their resolving power, but the total flux of the radiation available decreases accordingly, resulting in a lower signal-to-noise ratio (SNR) and longer exposure time. Nevertheless, the spectral resolution can be improved mathematically by removing the effects of the instrument response function. A constrained high-order cumulant algorithm is proposed to blindly deconvolute the measured spectroscopic data and estimate the response function of the instruments simultaneously. Experiments on artificial and real measured spectroscopic data demonstrate the feasibility of this algorithm.

Wavefront reconstruction from the transport-of-intensity equation (TIE) is a well-posed inverse problem given smooth signals and appropriate boundary conditions. However, in practice experimental errors lead to an ill-condition problem. A quantitative analysis of the effects of experimental errors is presented in simulations and experimental tests. The relative importance of numerical, misalignment, quantization, and photodetection errors are shown. It is proved that reduction of photodetection noise by wavelet filtering significantly improves the accuracy of wavefront reconstruction from simulated and experimental data.

High-quality crystals of gallium selenide (GaSe) and thallium arsenic selenide (Tl₃AsSe₃) were successfully grown. The refractive indices were measured in the subterahertz spectral region using time-domain spectroscopy. GaSe has a refractive index of 3.2 and an absorption coefficient of 1 cm^–1, along with an absorption peak at 0.6 THz. Tl₃AsSe₃ clearly shows birefringence, where the refractive indices are 5.0 and 5.4 along the fast and slow axes, respectively. The absorption coefficient is over 3 cm^–1 at 0.3 THz, increasing steadily with frequency.

We have proposed and demonstrated a novel signal-pump double-pass distributed Raman fiber amplifier (RFA) by using a three-port optical circulator as a reflective mirror. This unique RFA architecture not only doubles the amount of dispersion compensation, but also enhances the pumping efficiency. In comparison with the conventional signal-pump single-pass scheme, the proposed RFA has a 2.0-dB gain improvement and a 3.7-dB equivalent noise figure suppression, measured at 1598 nm. The proposed RFA may find wide applications in long-haul transmission and optical networks, where dispersion compensation is of great concern.

It is well known that propagation in an optical fiber alters the spectrum of ultrashort pulses due to the nonlinear interaction of the pulse with the fiber. The spectrum of the pulse as it emerges from the fiber depends on the input pulse parameters as well as the fiber parameters. We show by numerical analysis how this effect can provide a novel method to monitor with high sensitivity small relative changes in pulse characteristics of an ultrashort laser.

Modeling laser transmission welding of thermoplastics requires knowledge of the optical properties of the two materials being joined. Previous work measuring optical properties for this purpose placed little importance on the light reflection, emphasizing the light transmitted through a material. This paper presents work creating a low-cost solution allowing simultaneous measurement of the light transmission and reflection of clear rigid poly(vinyl chloride) from a diode laser source. Total reflection is quantified by numerically integrating measurements of the light reflection at specified locations around the perimeter of a sphere surrounding the sample; simultaneously the light transmission through the samples is measured. From a designed experiment involving two factors—surface finish and material thickness—the absorption coefficient of clear rigid poly(vinyl chloride) was calculated. In addition the quantity and distribution of light reflection was found to be dependent on the surface finish.

An annular beam provides a new laser drilling mechanism, which we refer to as optical trepanning. A refractive axicon system has been designed to transform an input Gaussian laser beam into a collimated annular beam. The diffractive effects of the axicon system and a convex lens focusing the collimated annular beam have been studied using the Fresnel diffraction integral. The theoretical diffraction patterns are compared with the patterns measured with a laser-beam analyzer. The results show that the refractive axicon system can produce Gaussian-like annular beams with the capability of easily adjusting the size of the annular beam.

The polarization characteristics of fiber Bragg gratings written into spun fibers with intrinsic birefringence and millimeter spinning periods are presented. Based on the Stokes parameter method, the evolution of states of polarization (SOPs) in spun fiber Bragg gratings is investigated. Their polarization-mode dispersion and polarization-dependent loss are measured in transmission and reflection. These spun fiber Bragg gratings always exhibit multiple side peaks near the Bragg peaks in their reflection spectra, and these reflection peaks have different polarization dependences on the input SOP. The polarization dependences are further analyzed in terms of the coupled-mode theory, and good agreement is obtained with the experimental results. Some potential applications are discussed.

A 40-channel 0.8-nm-spaced flat-top silica-based arrayed waveguide grating (AWG) with a tapered multimode interferometer (MMI) at the end of its input waveguide has been experimentally demonstrated for the first time. By adding the MMI, the 1-dB and 3-dB bandwidths are increased to 0.45 and 0.62 nm, respectively. The insertion loss (IS) of the device ranges from 3.8 to 6.8 dB. The IS uniformity is better than 3.0 dB. The crosstalk is better than –25 dB. Compared to the AWG with a rectangular MMI, the AWG with a tapered MMI shows better IS, crosstalk, and ripple.

The spectrum characteristic for the coupling between the core mode HE₁₁ and high-order cladding modes based on long-period fiber gratings (LPGs) is investigated with the aim of supplying a concrete concept to design narrow-bandwidth optical devices. In contrast to the better-known coupling between the core mode and low-order cladding modes, numerical simulation has shown that a 0.4-nm FWHM can be achieved by properly designing the period of the LPG in choosing the high-order cladding modes. In any case, in order to ensure that the analytic result for high-order cladding modes is meaningful, the validity of two-mode coupled-mode equations is also proved from the three-mode coupled-mode equations. According to this concept, LPG can be used to design not only gain flatteners that have wide bandwidth but also optical communication components that have narrow bandwidth to meet the ITU standard for a DWDM system.

A bidirectional dense wavelength-division multiplexing (DWDM) passive optical network (PON) based on injection-locked vertical-cavity surface-emitting lasers and a data comparator is proposed and demonstrated. Improved performance with respect to bit error rate and eye diagram was observed. Bidirectional transmission in DWDM-PON architecture is a very attractive option; the capacity of the optical network can be expanded relatively easily in that way.

A novel kind of optical fiber Raman amplifiers using time-division-multiplexed (TDM) pumping is analyzed. The equations governing the evolution of the pumps and signals are presented for both TDM forward and TDM backward pumping. Simulation results show that the performance in gain profile and ASE noise figure can be effectively improved. The optimal TDM pump repetition rates are between 2 and 8 MHz.

A new programmable expression for calculating the error probability in the presence of intersymbol interference and Gaussian noise for M-ary pulse amplitude modulation systems is derived by expanding the series method used in the evaluation of the error probability of binary symmetric channels. Error bounds for the expanded method are derived, and evaluation results for systems with Gaussian, Chebyshev, and sinc signaling are provided.

The signal of a novel waveguide multilayer memory (WMM) is the side-scattered beam emitted from information pits. Side scattering plays a key role in the data readout of the WMM. In this paper, a model is proposed to investigate the side-scattering properties of the WMM. We not only theoretically and experimentally confirm the exponential attenuation distribution of the side-emission scattered light intensity of a waveguide with constant attenuation coefficient, but also deduce an expression for the relation between the attenuation coefficient and the light propagation distance of a waveguide with distributed attenuation coefficient when the side-scattered light intensity is uniform. Furthermore, a possible method to realize the uniformity of the side-emitted light intensity is demonstrated. These results will contribute to the improvement of the performance of the WMM.

An optical highway for parallel interconnection of processors has previously been presented. Several matrix-vector multiplication algorithms are mapped onto the highway, and these are compared with traditional results. The practicalities of implementing such a design are then discussed with attention to possible fabrication routes and the polarization losses involved. This specifically involves mapping the parameter space of the angle of polarizing elements by a Monte Carlo method.

A dot-matrix hologram contains many two-dimensional grating dots, which may have different features, e.g., two-dimensional positions, grating pitches, grating orientations, and dot sizes. In this paper, such features are used to encode binary data to hide a figure almost without changing the hologram appearance. Because many encoding methods are available, decoding the hidden figure without authorization can be very difficult. The encrypting scheme presented here possesses both feasible and confidential features.

A high-performance hand-held thermal imaging camera has been developed, based on a 320×256-element InSb infrared focal plane array (FPA) operating in the medium-wave infrared region. The primary design objective was a low-cost, compact, lightweight, and portable thermal camera with a recognition range of 2 km. A staring FPA based on InSb technology with long and variable integration time provides the answer best suited to these requirements. The system provides such features as two-point and adaptive nonuniformity correction, bad-pixel detection and replacement, dynamic range compression, contrast and edge enhancement, histogram equalization, and digital scan conversion for CCIR-B-compatible output. The design methodology and the performance are presented.

This paper describes a series of perception experiments directed towards developing a model of moving target detection. The experiments systematically and precisely varied target size and speed, and found that the final probability of detection is primarily dependent on the size and did not depend on the speed. This, coupled with the finding that time to detect varied inversely with angular velocity as seen by the observer, indicated that the angular distance traveled across the display screen described the perception threshold for detection of a moving target. These findings, especially that the primary figure of merit associated with the detection of moving targets was angular displacement, have not previously been reported, apparently because earlier experiments confounded variables and made it difficult to separate the effect of target speed and time to detect on the overall psychophysical response. This new view holds promise for providing a fruitful lens through which to view the phenomenology of detection of moving targets and should assist in establishing new insights into the nature of motion perception.

The emissivity of a silicon wafer during the growth of thin oxide films was studied from the viewpoint of spectral, directional, and polarization characteristics of thermal radiation. Experimental results were mostly coincident with simulated results. By using a simulation model to estimate the optical properties of silicon wafers, a direct relationship was found between the ratio of p- to s-polarized radiance and the polarized emissivity under specific conditions. This relationship was experimentally confirmed at high temperatures (>900 K). On the basis of these results, the present study proposes a new radiation thermometry technique that can measure the temperature and spectral polarized emissivity of a silicon wafer at a wavelength of 0.9 µm and at moderately high temperatures, irrespective of the variation in emissivity with oxide film thickness.

One of the most challenging research topics in the field of target detection in electro-optical images is the relationship between image content and human detection performance. We propose two target structure similarity (TSSIM) metrics to describe global image clutter. Via a simple mathematical formula, the TSSIM clutter metrics and their combinations with different local target-to-background contrasts, which are loosely referred to as signal-to-clutter ratios (SCRs), are used to predict human detection performance. Other clutter measures and their combinations with the contrast ones are also considered for comparison. The degrees of correlation between target detection probabilities and various clutter metrics, as well as the SCR models, are presented. Experiment results show that the TSSIM measures are more suitable for quantifying electro-optical clutter than other clutter measures compared. And the SCR metric, which combines the root-sum-of-squares local contrast and a TSSIM clutter metric, generates the best predictive capabilities for the experimental detection probabilities.

This paper describes a visual cryptography method for the elimination of pixel expansion and the improvement of contrast. The proposed method uses the probability concept to construct a multiobjective linear programming model for general access structures. Then, the solution space of the model is explored by goal programming. The advantages of the proposed method are fourfold. First, it can avoid expanding the shadow images. Second, it can reach better contrast. Third, it can deal with general access structures and get the desired contrast levels. Fourth, it can be easily extended to deal with the problems of multiple secret images. Experiments on several access structures show that the proposed method is effective against pixel expansion and is capable of contrast improvement.

Spectral signature coding is an effective means of characterizing spectral features. This paper develops a rather different encoding concept, called progressive signature coding (PSC), which encodes a signature in a hierarchical manner. More specifically, it progressively encodes a spectral signature in multiple stages; each of these stages captures disjoint spectral information contained in the spectral signature. As a result of this progressive coding, a spectral profile of progressive changes in a spectral signature can be generated for spectral characterization. The proposed idea is very simple and evolved from the pulse code modulation (PCM) commonly used in communications and signal processing. It expands PCM to multistage PCM (MPCM) in the sense that a signature can be decomposed and quantized by PCM progressively in multiple stages for spectral characterization. In doing so, the MPCM generates a priority code for a spectral signature so that its spectral information captured in different stages can be prioritized in accordance with significance of changes in spectral variation. Such MPCM-based progressive spectral signature coding (MPCM-PSSC) can be useful in applications such as hyperspectral data exploitation, environmental monitoring, and chemical/biological agent detection. Experiments are provided to demonstrate the utility of the MPCM-PSSC in signature discrimination and identification.

Cone-beam computed tomography (CBCT) is a three-dimensional (3-D) imaging modality. The spatial blurring or spatial resolution of a CBCT system can be quantitatively characterized by a 3-D point spread function (PSF), which can be experimentally measured through the use of a small ball phantom and an edge-blurring algorithm. A solid ball offers a number of step edge functions along its radial lines, in terms of density profile. The CBCT system PSF is responsible for blurring a step edge into a spread edge, which can be determined by an iterative algorithm. By a spatial separability assumption, a 3-D PSF can be decomposed into 2-D and 1-D PSFs. The spatial shift variance refers to the nonuniform distribution of PSF full width at half maximum (FWHM) over the object domain. The anisotropic blurring is reflected by the blurring differences along three orthogonal directions of a PSF ellipsoid. The experimental results show that our CBCT system varies in the range between 0.43 and 0.82 mm in the object domain of 80×80×120 mm³, and the anisotropy of 3-D PSF is generally insignificant and is bounded by 0.04 mm.

The encoding of vector quantization (VQ) needs expensive computation for searching the closet codeword to the input vectors. To reduce the computational burden, many researchers have developed some efficient full-search-equivalent algorithms by using the characteristics of the mean values and variances of an input vector to reject unlikely codewords. However, some computational redundancies still exist. As far as we know, Pan's method has the best performance of rejecting unlikely codewords using both characteristics. In this work, we introduce a technique to efficiently partition a vector into two dynamic subvectors according to the patterns inside the block (or vector), and then further improve the computational load given by Pan's method. Experimental results show that the proposed method is superior to other algorithms in terms of processing time and the number of distortion calculations. Compared with the best encoding algorithm, our algorithm can further reduce the processing time and the number of distortion calculations for various codebook sizes by 14.7 to 41.3% and 14.9 to 44.6%, respectively.

We propose a two-stage real-time tracking algorithm for an active camera system having pan-tilt-zoom functions. The algorithm is based on the assumption that a human head has an elliptical shape and that its model color histogram has been acquired in advance. The algorithm consists of two stages, a color-based convergence stage for fast and reliable tracking and a refinement stage for accurate tracking based on multimodal information. In the first color convergence stage, we roughly estimate the target position by using the mean-shift method based on the histogram similarity between the model and a candidate ellipse. To better predict the initial position for the mean shift, the global motion is compensated; to enhance reliability of the mean shift, the model histogram is appropriately updated by referring to the target histogram in the previous frame. In the subsequent refinement stage, we refine the position and size of the ellipse obtained at the first stage by using multimodal information such as color, shape, and quasi-spatial information. In particular, to quantify the quasi-spatial information, we use a spatial color histogram obtained by properly dividing the ellipse into two regions. Extensive experiments verify that the proposed algorithm robustly tracks the head, even when the subject moves quickly, the head size changes drastically, or the background has many clusters and/or distracting colors. Also, the proposed algorithm can perform real-time tracking with a processing speed of about 10 fps on a standard PC.

Digital watermarking has been widely studied for the copyright protection of digital multimedia data. In traditional digital image watermarking techniques, a watermark signal is inserted into the host image, which generally introduces visual quality degradation. On the contrary, zero-watermark techniques extract some features from the host image and use them for watermark detection, instead of watermark embedding. In this method, the distortion problem to the host image due to watermark embedding is eliminated. The zero-watermark scheme proposed in this work employs neural networks for features extraction. It can be used for automatic piracy detection as well as copyright demonstration if it is associated with a copyright authentication center.

The high demand for multimedia applications has emphasized the requirement for newer methods for the transmission of video over low-bit-rate error-prone channels. H.264 video coding provides a versatile video coding format suitable for different network and storage applications. The versatility is exposed through a set of encoder control parameters. We investigate the effects of these parameters on the rate, distortion, and algorithm complexity and determine a suitable set of parameters, keeping the low bit-rate wireless channel in perspective. Rate-compatible punctured convolutional coding is used to produce code rates varying from 8/9 to 1/4 using the same encoder and the same Viterbi decoder. A feedback-based adaptive forward error correction (FEC) technique is developed to use the rate compatible codes in the transmission of video, which is especially vulnerable to transmission errors because of the high compression using predictive coding. The proposed system is used to perform joint source-channel coding of video and to study the effects over mobile channel over various E_b/N₀ values. The results are used to develop a channel-adaptive system for the transmission of video over low bit-rate channels. Frame-by-frame adaptation of the video to the channel conditions is simulated to demonstrate that proposed channel-adaptive joint source-channel coding of H.264 video could utilize the available channel capacity more efficiently than a fixed-coding-based system when transmitting over low-bit-rate error-prone channels.

A fast intramode SKIP detection algorithm based on the rate-distortion (RD) cost for an interframe (P slices) is proposed for H.264/AVC video encoding. There are three types of intrapredictions according to profiles. These are 16×16 and 4×4 intrapredictions for luminance and an 8×8 intraprediction for chroma. For the high profile, an 8×8 intraprediction is added for luminance. The 4×4 prediction mode has nine prediction directions with four directions for 16×16 and 8×8 luma, and 8×8 chrominance. In addition to the intermode search procedure, an intramode search causes a significant increase in the complexity and computational load for an interframe. To reduce the computational load of the intramode search at the interframe, the rate-distortion (RD) costs of the neighborhood MBs for the current MB are used, and we propose an adaptive thresholding scheme for the intraSKIP extraction.

Classifier combinations can be used to improve the accuracy of demanding image classification tasks. Using combined classifiers, nonhomogenous images with noisy and overlapping feature distributions can be accurately classified. This can be made by classifying each visual descriptor first individually and combining the separate classification results in a final classification. We present an approach to combine classifiers in image classification. In this method, the probability distributions provided by separate base classifiers are combined into a classification probability vector (CPV) that is used as a feature vector in the final classification. The proposed classifier combination strategy is applied to the classification of natural rock images. The results show that the proposed method outperforms other commonly used probability-based classifier combination strategies in the classification of rock images.

We present a new image segmentation algorithm based on Markov random fields (MRF) with adaptive neighborhood (AN) systems. First, a new criterion function is developed to adaptively select the neighborhood system of the MRF. Second, thanks to the appropriate format of the new criterion function, a general iterated conditional mode (GICM) is deduced to incorporate the AN selection into the inference process in the segmentation of images. Third, an end points detection step is introduced to preserve the ends of line structures in the images. The proposed algorithm has the following advantages over previous works: the convergence of the new algorithm is much faster than classical algorithms; the AN configuration of each site is iteratively optimized in the inference process, which leads to more accurate segmentation results; and no extra knowledge is needed in the AN selection. Numerical experiments on a wide range of images demonstrate that the proposed image segmentation algorithm performs better, in terms of speed and detail preserving, than the algorithms based on classical MRFs.

A transmitting process of a sequence of holograms describing 3-D moving objects over a communicating network system is presented. A sequence of holograms involves holographic information of 3-D moving objects recorded as fringe patterns. In this process, holographic information recorded in the holograms is transformed into bit stream data, and then is transmitted over the Internet. We call this process a "network streaming technique." It is shown that by applying this network streaming technique, holographic data of 3-D moving objects are transmitted in high quality, and a relatively good reconstruction of the holographic images is performed. Moreover, it suggests that if this network streaming technique is employed together with MPEG-4, a new transmitting process for holographic information of 3-D moving objects may be rigorously developed over network systems, and will play a very important role in this field.

New discoveries in astronomy require the use of ever larger telescopes. These telescopes require segmented apertures, since current technology does not provide for the fabrication of monolithic mirrors with diameters much larger than 8 m. As a result, the point spread function (PSF) of the system presents a diffraction pattern characteristic of the segmentation geometry, and this complicates the task of detecting faint structures with high spatial resolution. In this work, we investigate the use of amplitude filters at the pupil plane to decrease the intensity of this diffraction pattern. It is sufficient if this diffraction pattern is reduced below the residual halo that remains after adaptive optics compensation, so that the intensity distribution that surrounds the PSF core is limited by scattering rather than diffraction. We show different kinds of filters that allow us to achieve this goal. We analyze their performance, taking into account some unavoidable errors in the telescope operation such as imperfect phasing of the telescope segments and gaps between them. Finally, we discuss the application of the technique considering errors in the adaptive optics correction.

A motorized rotating retarder, a linear polarizer, and a digital camcorder are used to obtain polarization profiles of natural daylight scenes. A correlation technique synchronizes real-time video frames with respect to the rotating retarder's fast axis. Polarization parameters are calculated for each red-green-blue (RGB) channel and scene pixel. Extending the quasimonochromatic approximation to larger bandwidths is solved by expressing the Stokes parameters explicitly as functions of wavelength. A detailed numerical analysis examines errors due to ill-conditioning effects that are associated with specific relative angular orientations of the optical components. A comparison of the theoretical results with empirical data from the digital camcorder provides a validation process for the results in this paper. A RGB pseudocolor encoding algorithm provides a means to visualize the polarization imagery. An ellipticity study was conducted during the early morning hours when scene lighting conditions change rapidly. A comparison of the results from a digital still camera, using a 30-s data acquisition time period, was made with respect to a 0.6-s time period for the rotating retarder configuration. The results clearly show that errors due to temporal registration effects are dramatically reduced as the time interval between images goes to zero.

Radially polarized illumination produces, in combination with annular pupil filtering, the sharpest focal spot. However, the enhanced sidelobes produce an effective deterioration of spatial resolution. This study shows that if one substitutes the annular filter by one, adequately designed, shaded-mask filter, the sidelobes' strength is strongly reduced, and an important, effective improvement of resolution is achieved.

A new technique is proposed for optical encryption and multiplexing of binary characters and images used for personal identification information. Different binary images can first be encrypted using orthogonal code and then multiplexed together in the spatial domain. The resulting encrypted single image provides security as well as makes efficient use of storage and/or transmission capacity. The image can finally be decrypted and the individual input images can be decoded employing the same orthogonal code set. Because of the orthogonal nature of the code used, the encryption and decryption processes do not deteriorate the quality of the images employed. Also, the proposed technique involves a very simple architecture, as it does not require any mathematical transformation.