This PDF file contains the editorial ““Don’t be lazy.”” for OE Vol. 46 Issue 04

A novel all-optical set/reset flip flop (AOFF) based on a symmetric Mach-Zehnder switch with a feedback loop and multiple forward set/reset signals is presented. The proposed flip flop has a fast response, a flat output gain, and a short switching-on interval of a few hundreds of picoseconds regardless of the associated feedback-loop delay. It is shown that a high on/off constrast ratio at the AOFF output is achieved above 20 dB.

Low quality images are often corrupted by artifacts and generally need to be heavily processed to become visually pleasing. We present a modified version of unsharp masking that is able to perform image smoothing, while not only preserving but also enhancing the salient details in images. The premise supporting the work is that biological vision and image reproduction share common principles. The key idea is to process the image locally according to topographic maps obtained from a neurodynamical model of visual attention. In this way, the unsharp masking algorithm becomes local and adaptive, enhancing the edges differently according to human perception.

We introduce a fast partial difference elimination (PDE) algorithm for motion estimation (ME). The basic idea of the proposed approach is to eliminate invalid candidates earlier by predicting a total matching error between matching and candidate blocks. The matching error prediction is performed by using a partially computed matching error between the blocks. Experimental results show that the proposed algorithm can significantly save about 40% of the averaged computational costs versus the conventional PDE algorithm for ME at the cost of ignorable image quality degradation, whose average value is 0.0012 dB.

A fast motion estimation algorithm based on the adaptive search range adjustment (ASRA) is presented. The size of search range for each block is adaptively controlled according to the initial cost at the search center, and then the full search algorithm (FSA) is performed to find the optimal matching block in the adjusted search range. The proposed method is implemented in H.264/AVC reference software (JM) to demonstrate its efficiency over the conventional FSA.

We propose a simple technique to determine the distance to an object from two passive photometric measurements. The technique offers the possibility of developing fast and inexpensive passive optical range sensors for different applications.

Precision phase-contrast imaging has been achieved with in-line phase-shifting digital holographic microscopy. The complex amplitude of the object field on the charge-coupled device plane is measured by the phase-shifting method with a self-calibration algorithm, and the magnified object image is reconstructed with a plane wave expansion method. The phase fluctuation in the blank image without sample is 1.30 deg and the three-dimensional shape of a titanium phase test pattern is measured with an accuracy of 5.51 nm (corresponding to the phase resolution of 3.63 deg), which are better than those of off-axis systems.

Postdeposition chemical etching of spectral-hole filters, which were fabricated as chiral sculptured thin films with central 90-deg-twist defects, decreases the cross-sectional dimensions of the helical columns that such films comprise and blueshifts the spectral holes, thereby establishing the efficacy of postdeposition chemical etching as a means to tune the optical response characteristics of sculptured thin films.

We present a new electro-optic (EO) tunable bandpass filter design based on a long-period-grating-assisted asymmetric waveguide coupling mechanism. A narrow passband width of <0.2 nm and a large wavelength tuning range exceeding 30 nm can be obtained at a low driving voltage of ~16 V. This type of EO tunable filter would form key building blocks in dynamic wavelength division multiplexing (WDM) optical networks.

We present the fabrication process of straight-ridge Yb³⁺:Er³⁺ co-doped Al₂O₃ waveguides. Thin films are synthesized on silica-on-silicon wafers by middle frequency sputtering (MFS) and microwave ECR (MW-ECR) plasma source deposition. Waveguides are developed by reactive plasma etching employing BCl₃ gas. Photoluminescence (PL) spectrum and gain measurements at 1.53 μm are investigated at room temperature: a net gain of 5.225 dB/cm is achieved from a 10.5-mm-long waveguide obtained by MFS, and 0.043 dB/cm is achieved from a MW-ECR with a 980-nm pump power of 62 mW.

High brightness light emitting diodes (LEDs) become a serious alternative for ultrahigh performance lamps in projection displays. We focus on the illumination part of a LED projection engine. We discuss the problem of using several LED light sources for each primary color. In critical applications, the use of several light sources for each color has important benefits. It increases the possible light output to the screen and makes it possible to design a system that is tolerant for failures of one of the LEDs. Therefore, we need an optical system that is both efficient and is able to produce a uniform light beam if one of the LEDs fails. We show that our illumination engine using a fly's eye integrator meets these requirements, using ray-tracing simulations of the engine. An efficient optimization method based on the simplex method [R. J. Koshel, Opt. Lett. 30, 649–651 (2005)] was developed to design the LED collimation reflective device with collection efficiencies up to 95%. The lens systems in the engine were designed with the same method. This results in a total system efficiency of 77%.

This paper employs a regional partition approach to establish the optimal distribution of the diffuser dots in the light guide of an edge-lit backlight. The proposed approach commences by dividing the light guide into a number of partitions and assigning an equal radius to every dot. An iterative optimization procedure is then performed in which the illuminance in each partition is calculated and the dot radius in each partition progressively adjusted until uniform luminance is obtained over the entire light-guide surface. To simplify the geometry construction process and improve the efficiency of the optimization procedure, a simple optical model is proposed for the diffuser dots and the bare surface of the light guide, and an analytical procedure is implemented to take account of the diffuser-film and brightness-enhancement-film effects. The simulation results confirm the ability of the proposed approach to accurately reflect the fine regulation of the dot radius required to obtain uniform luminance for typical light-emitting diode configurations used in practical backlight modules.

The BepiColombo Laser Altimeter (BELA), part of the payload of the European Space Agency's BepiColombo mission, is designed to point a telescope with a 200-mm aperture toward a surface that can reach 700 K. Furthermore, direct sunlight can shine into the instrument at angles of ≥ 38 deg from the boresight. At Mercury, the solar flux can exceed 14 kW m^-2. A baffle for such conditions must both reduce straylight to the best possible extent and minimize the heat load to the spacecraft, i.e., the sum of absorbed visible light and infrared flux. We describe the design and manufacture, including coating, of a reflective baffle. The baffle is made by diamond turning of aluminum and has a clear aperture of 200 mm, about 300-mm length, and a mass of 716 g.

Space-borne optical systems must be tolerant to radiation to guarantee that the required system performance is maintained during prolonged mission times. We show that the radiation hardness can be improved by selecting the relevant glass from a group of optical analogs. This conclusion is based on the study of gamma-radiation-induced absorption of crown glasses from group 517640 (glasses with n_d≈1.517 and ν_d≈64)—BK7 and NBK7 (Schott), S-BSL7 (Ohara), BSC 517642 (Pilkington), and K8 (NITIOM). Our results show that whereas these glasses are optical analogs before irradiation, they behave differently during and after irradiation.

To improve airborne search and rescue operations and the general aerial surveillance efficiency, new concepts of multiple field-of-view and variable-resolution imagers have been developed. These imagers provide surveillance operators with simultaneous wide area coverage and high-resolution imaging. Over the last years, several optical steering systems have been developed and field tested in operational conditions. These developments helped us to develop a novel camera steering system using achromatic Risley prisms. This simple and sturdy steering system allowed us to move rapidly and precisely the field of view of an infrared camera. To improve its performance, a three-dimensional (3D) refraction model was applied to enable fast pointing direction calibration and correction of distorted images. Image deformations were analyzed, and a fast linear image correction based on homographic transformation and the 3D refraction model are presented. Experimental results of mosaicking applications with real imaging systems in the 3- to 5-μm, 8- to 12-μm infrared, and 850- to 860-nm visible bands demonstrate the improvements achieved with the homographic image distortions correction and the fast pointing calibration procedure.

A denoising technique based on filtering the coefficients of a redundant wavelet transform is proposed for the purpose of reducing statistical noise in images without blurring sharp edges. The wavelet coefficients in the higher-spatial-frequency components are denoised using a function that has been used in nonlinear diffusion filtering. With this function, edge and noise points were correctly distinguished. This resulted in the elimination of the wavelet coefficients at the noise points and the preservation of the wavelet coefficients at the edge points. As a result, most of the image noise was successfully eliminated without appreciable losses in the sharp edges. Thus, the denoising technique coped with both noise reduction and edge preservation.

Segment-based stereo matching algorithms are not able to deal with the difficulty that disparity boundaries appear inside the initial color segments. To solve this problem, we propose a novel algorithm that segments the reference image by combining color and depth segmentation information. Then we construct the energy function in segment domain, which embodies the smoothness and visibility constraints to penalize the discontinuities of edge pixels and potential occluded regions, respectively. Finally, the optimal disparity plane labeling is approximated by applying loopy belief propagation. Experimental results on the benchmark images demonstrate that our algorithm is comparable to the state-of-the-art algorithms.

We have fabricated a complex-shaped mirror array and evaluated its fabrication accuracy. The mirror is constructed with 16 mirror elements with an arc-shaped contour and a spherical reflective surface, and is part of an arc-shaped fly-eye mirror for use in an extreme ultraviolet lithography system. All the mirror elements are manufactured individually, using single-crystal silicon as the mirror material, and are then arranged side by side on a base plate by magnetic attraction. The spherical mirror elements are manufactured to have highly accurate and smooth surfaces, although they have a different shape from those of general optics, and are assembled to form the fly-eye mirror. To evaluate the positioning errors of the mirror elements of the assembled fly-eye mirror, an optical testing system using visible rays are developed. From the measured results using this system, the average tilt error of the mirror elements is 69 arcsec, assuming that the system has a collimation error, which we corrected through calculation. Thus, the fly-eye mirror is fabricated with a high accuracy, demonstrating that the fabrication process is useful in realizing complex-shaped mirrors.

The thermal reflow process is widely used in microlens array fabrication. However, the resulting arrays are commonly criticized for their low fill factor. In this work, caulking is applied to fill the gaps between adjacent lenses. The experimental results prove that a gapless microlens array with a 100% fill factor could be successfully produced and the caulking time precisely controlled. Furthermore, an artificial neural network and genetic algorithm are used to achieve high quality using the thermal reflow and caulking. The L18 orthogonal array is used as the learning data for the artificial neural network to construct a system model that could predict the results (e.g., S/N, focal length, and roughness) for arbitrary parameter settings. The genetic algorithm is then applied to obtain the optimal parameter settings. The major objectives in using the optimal design are to reduce the variation in the focal length and the surface roughness for a microlens array. This allows improved focus and enhanced illumination brightness. The results show that microlens array quality could be significantly improved in comparison with the original design.

In phase-shifting-based fringe-projection surface-geometry measurement, phase unwrapping techniques produce a continuous phase distribution that contains the height information of the 3-D object surface. Mapping of the phase distribution to the height of the object has often involved complex derivations of the nonlinear relationship. In this paper, the phase-to-height mapping is formulated using both linear and nonlinear equations, the latter through a simple geometrical derivation. Furthermore, the measurement accuracies of the linear and nonlinear calibrations are compared using measurement simulations where noise is included at the calibration stage only, and where noise is introduced at both the calibration and measurement stages. Measurement accuracies for the linear and nonlinear calibration methods are also compared, based on real-system measurements. From the real-system measurements, the accuracy of the linear calibration was similar to the nonlinear calibration method at the lower range of depth. At the higher range of depth, however, the nonlinear calibration method had considerably higher accuracy. It seems that as the object approaches the projector and camera for the higher range of depth, the assumption of linearity based on small divergence of light from the projector becomes less valid.

The long trace profiler (LTP) is a useful optical metrology instrument for measuring the figure and slope error of cylindrical aspheres commonly used as synchrotron radiation (SR) optics. A multiple-function LTP (LTP-MF) is developed at the optical metrology laboratories of Brookhaven National Laboratory (BNL) with a goal of increasing the accuracy of the measurement and extending the range of applications to other areas. Characteristics of the LTP-MF are a very compact and lightweight optical head, a large angular test range (±16 mrad), and high accuracy. The LTP-MF can be used in various configurations: as a laboratory-based LTP, as an in situ LTP or penta-prism LTP, as an angle monitor, as a portable LTP, and as a small-radius-of-curvature test instrument. The system configuration, designs of the compact optical head and slide, and analysis of different measurements modes and systematic error correction methods are introduced. Preliminary comparison measurements between the LTP-MF and the LTP-II are presented.

The aberration introduced by the primary optical element of a lightweight large aperture telescope can be corrected with a diffractive optical element called the liquid crystal spatial light modulator. Such aberration is usually very large, which makes the design and modeling of such a system difficult. A method to analyze the system is introduced, and the performance limitation of the system is studied through extensive modeling. An experimental system is demonstrated to validate the analysis. The connection between the modeling data and the experimental data is given.

Spectral and temporal influence of a conventional half-wave plate–polarizer attenuator on broadband 50-fs laser pulses is experimentally investigated. Strong spectral modulation, pulse narrowing, and pulse shape variation of the transmitted femtosecond laser beam are recorded at maximum attenuation together with substantial depolarization effect. A simplified theoretical model is developed to take account of the wavelength dependence of the wave plate, which provides satisfactory explanations to the experimental observations.

Laser welding technology is widely used in fiber optic components assembling. A big issue in fiber optic packaging using laser welding is the welding-induced alignment distortion (WIAD), which significantly reduces the fiber optic coupling efficiency. Various studies have been conducted to investigate the factors affecting the WIAD in butterfly laser module packaging, but the influence of laser parameters on the WIAD remains unnoticed. We present a study in minimizing the WIAD by laser pulse shape. Finite element method is employed and a realistic laser-materials interaction model is developed and incorporated into the analysis to investigate the influence of six types of laser pulse shape on the WIAD in the butterfly packages. The results show that the pulse shape significantly affects WIAD. Ideally, a properly selected pulse shape can eliminate or minimize the WIAD in the butterfly laser module packages.

The design and construction of a system to accurately determine the speed of a projectile (bullet) by measuring the time of flight between two parallel laser screens is described. Each screen is formed by a laser source and a set of prisms. At the detection end of each of the screens, a collector lens focuses the incident laser light beam onto a photodetector. The collector lens and detector are kept in a recess so that no stray or ambient light falls on the photodetector. Whenever a projectile crosses either of the screens, the corresponding photodetector senses the event, due to partial or full obscuration of the incident energy. An electronic circuit is used to accurately record the time when the projectile crosses each screen, and the time interval gives the time of flight. The distance between the screens being known, the velocity is displayed on a computer screen. Because a single collimated beam of light generates the entire optical curtain, the reduction in incident energy at the photodetector plane is independent of the entry point of the projectile into the screen. Due to the baffling of the photodetector from ambient light, the optical screens can be used at indoor or outdoor ranges equally effectively.

The model used for analyzing the gain characteristics of Er-Yb–doped phosphate glass waveguide amplifier (EYDWA) with forward-backward pumped configuration (FBPC) is based on the rate and optical power propagation equations, which include forward-backward pump, upconversion mechanisms, and light propagation loss. An overlap factor, which considers the difference between signal and pump field intensity distribution in channel waveguides, is introduced to evaluate the gain of EYDWA. The results show that FBPC can make the pump power light more uniform and lower than that in forward-pumped configuration (FPC), inhibiting the upconversion. Thus, FBPC increases the gain of the device by 2 to 3 dB compared with FPC, and pump conversion efficiency (PCE) is accordingly raised by 50%. The total power of amplified spontaneous emission (ASE) is also higher than that in FPC. The gain of EYDWA is affected obviously by the pump configuration, modes of pump light, upconversion coefficient, and scattering loss. Moreover the detrimental effect due to the above factors is reduced by the FBPC.

Light-wave switching with optical circuits consisting of directional couplers and amplifiers is discussed. Designing of the switch structure using coupled mode theory is proposed. Using some configuration examples, we find that the light-wave switching is feasible when several conditions involving angles are maintained by properly controlling the intensity of the propagating light wave. When waveguide-type Raman amplifiers are employed as the amplifiers, wavelength-selective switching can be realized. Switching characteristics in a proposed circuit are clarified with regard to their dependence on wavelength and phase.

We report a design for a small-residual-dispersion fiber system suitable for all wavelengths in the range of 1480 to 1610 nm, which covers the entire S to L bands. It consists of a small-relative-dispersion-slope fiber (SRDSF) with a flat modal field over the central part of the core, and the corresponding dispersion-compensating fiber (DCF). The SRDSF has mode field diameter (MFD) <10 μm at wavelength λ0=1.55 μm, leading to the large effective area (Aeff≈ 95 μm²) required to reduce nonlinear effects, and dispersion 9.5 ps/(km nm) with small relative dispersion slope <0.003 nm−1 at λ0=1.565 μm. The DCF, which is based on the dual-core coaxial configuration, has large negative dispersion [ ≈−248 ps/(km nm) at λ0=1.565 μm], leading to a large figure of merit (FOM). The dispersion slopes of these fibers are so adjusted that a small length of DCF will compensate the accumulated dispersion in the SRDSF simultaneously at all wavelengths in the range of 1480 to 1610 nm. The maximum values of the effective dispersion of the fiber system and its slope are about ±0.2 ps/(km nm) and ±0.03 ps/(km nm²), respectively, in the entire wavelength range of 1480 to 1610 nm.

The input power dynamic range and switching speed of an optical switch matrix based on cascaded semiconductor optical amplifier (SOA) gates with holding-light injection were studied numerically using the carrier-density rate equation of the SOA and a dynamic bit-error-rate calculation method. It is shown that holding-light injection can effectively extend the input power dynamic range to high signal input powers, on account of the suppression of the patterning effect in the presence of holding light. Moreover, cascaded SOA gates tend to provide a more linear output-input relation with holding-light injection. A useful by-product of holding-light injection is the enhanced switching speed of the SOA. The switch-on time with holding light is always shorter than that without, owing to a shorter carrier lifetime in the presence of holding light.

Intensity distributions of linearly polarized (LP) propagation modes of several orders are plotted for a step-index elliptical-core dielectric waveguide. A simplified characteristic equation is obtained through the weakly guiding approximation, which can be used to find the propagation constants and the cutoff frequencies of each LP mode. These constants are then applied to the solution of the scalar wave equation, which is expanded in series of ordinary and modified Mathieu functions, to obtain the intensity patterns of the LP modes. Results are compared with previous work, and it is found that when the elliptical core tends to a circle (ratio of semimajor to semiminor axis equal to 1.0001) our cutoff frequencies are closer to the LP-mode cutoffs of the circular fiber than are the cutoffs obtained in other papers on elliptical fibers.

We propose a novel survivable algorithm, called backup-shared with trap avoidance (BSTA), to protect against single failure with shared-risk link groups (SRLGs) in wavelength-division multiplexing optical networks. In BSTA, each connection request will be assigned one primary path and one SRLG-disjoint backup, or one primary path and two SRLG-disjoint segment-backup paths. In contrast with previous algorithms, BSTA not only can effectively avoid the trap problem, but also can obtain better resource utilization ratio and lower blocking probability. Simulation results are shown to be promising.

Based on the chirp-pulse compensation technique, a 40-GHz supercontinuum (SC) source generated in a highly nonlinear fiber (HNLF) with large normal dispersion is investigated. We show numerically and experimentally that the widest SC spectrum can be obtained by setting a two-stage all-fiber pulse compressor consisted of the HNLF and standard single-mode fiber (SMF) in front of the last-section HNLF for SC generation. The third dispersion of the fibers, especially the SMF used as chirp-compensating fiber, is found to greatly degrade the SC spectrum generated in this scheme.

By designing multiple single-mode cores across the multimode fiber core area, this new multimode fiber can support only the fundamental mode or fewer low-order modes propagation to some extent. Therefore, the modal dispersion of the multimode fiber has been suppressed greatly, and the bandwidth is enhanced 6.5 times.

We present a 1:2 variable optical splitter (VOS) with a self-latching property. This new generation of optical coupler presents two coupling ratio states (50%–50% and 100%–0%) and is based on magneto-optical technology. Fabricated VOS has an intrinsic loss of about 1 dB with a polarization-dependent loss (PDL) less than 0.1 dB. The flatness of the optical characteristics has also been measured in the C+L band at various temperatures. The active optical component needs an electrical pulse (with τ=1 ms) of around 2 V and 60 mA to be activated. Various passive optical network (PON) architectures using active 1:2 VOSs with self latching are investigated here. These components are cascaded to make a splitter with a tunable number of branches. The use of this splitter allows the achievement of adaptive, flexible, and scalable optical network architectures. The devices can be implemented in the central office (CO) or in the middle of the network. Last, we propose a remote powering and/or monitoring technology using a fiber-optic link in order to activate the dynamic optical power splitter. The key element of this technology is a pigtailed power converter module. The powering system avoids use of a local power supply via a power line and/or battery, maintains the passive and reliable properties of the network, and significantly limits its cost.

Contamination at the head-disk interface (HDI) was observed for first-surface near-field recording (NFR) under accumulation over a long writing time with a high writing power. The contamination was caused by laboratory dust coupled with the heat from the focus of the writing laser at the HDI. One suggested solution to the problem is that a cover layer should be laminated for cover-layer-incident NFR. A uniform and edge-bead-free UV-curable cover layer was laminated by using an outer-ring technique. Diamondlike carbon films were optimized and coated on the cover layer, and then a lubricant film was applied to reduce the tribological problems at the HDI.

The complex Fresnel field that contains three-dimensional (3-D) information about an object can be retrieved from an optically generated and electronically detected single off-axis Fresnel hologram of a 3-D object. The retrieved complex Fresnel field gives the appearance of a noise-like distribution. This is primarily due to the scattering nature of the object and the resulting speckle noise, which is a salient trait of the reconstruction process of a hologram. We describe a possible method for securing holographic information by digital encoding of the Fresnel field. A single random-phase Fourier plane encoding is carried out with an assumption that the noisy nature of the complex field may be equivalent to the primary random mask-bonded field, as in the case of conventional double random-phase Fourier plane encoding. The analogy between the decryption process and the numerical reconstruction of the hologram leads to a single-step reconstruction of the complex object field from the encrypted Fresnel field, thus saving computational power. The use of a single off-axis hologram is helpful in zero-order and twin-image free reconstruction. The algorithm is explained with experimental results to support the proof of the concept.

We present an experimental confirmation of optical properties of multiplane holograms designed with our novel iterative method. The method allows encoding many input intensity distributions into a single phase-only hologram. The object planes can be placed at variable distances, and their content is fully customizable. The reconstructed three-dimensional (3D) scenes exhibit high contrast and low noise level in all designed image planes. The results of numerical simulations are compared with those of a reconstruction in an optical setup. Holograms for optical reconstructions were manufactured using two methods: photographic and electron beam lithography (EBL). Experimental results achieved with both methods are compared. We present our research on a new class of iterative holograms, containing up to eleven object planes, designed in close distance to each other. The elements exhibit unusual light focusing possibilities and extraordinary imaging properties, thus introducing a number of possible practical applications, which are discussed.

The reproduction of computer-generated hologram (CGH) with white light source was realized using a liquid crystal panel instead of holographic film. The Burch-coding CGH was achieved by simulating the interference of a digital image and virtual reference light, displayed on liquid crystal displays and illuminated by a white light-emitting diode. The system is compact and the reconstructed images include full parallax. The full-parallax images of the Fresnel hologram computed with our algorithm were compared with the reproduced images by the rainbow hologram. The results implied this method was ready for the development of real-time three-dimensional color digital holography.

The use of diffusers in space-based spectrometers leads to the creation of speckles, in the entrance slit. Due to these speckles, unwanted modulations in the measured spectral data are observed. We explain the origin of these unwanted modulations, which we refer to as speckle-induced spectral features or, in short, spectral features. A single value is introduced that can be used to indicate the effect of the speckle-induced spectral features, the spectral feature amplitude (SFA). Measurement and modeling of the SFA parameter on aluminum diffusers are presented.

Unlike conventional video-based face recognition systems, in which the tracking and recognition are considered as two independent components, this paper presents a new integrated framework for simultaneously tracking and recognizing human faces. In this framework, tracking and recognition modules share the same appearance manifold. During training, because locally linear embedding (LLE) can detect the meaningful hidden structure of the nonlinear face manifold, LLE combined with K-means is employed to assign face images of every individual into clusters to construct view specific submanifolds. To improve the robustness of tracking and recognition, robust locality-preserving projection is developed to obtain linear subspaces that approximate the nonlinear submanifolds. Dynamics is also learned during this period. During testing, to reduce the great computational load, the integrated posterior probability is partitioned into two independent probabilities, which are obtained by a particle filter and by maximum posterior estimation by Bayesian inference, respectively. Extensive experimental results show that our proposed framework is effective for tracking and recognition under significant variations in pose, facial expression, and illumination and under scale variations and partial occlusion.

A region-growing algorithm requires knowledge of the position of seed points in advance and must prespecify a threshold for the homogeneity test. Thus, the process of image segmentation by this algorithm cannot be implemented automatically, which often restricts its application in engineering practice. We propose an adaptive region-growing algorithm for automatically extracting small targets from an IR image. Using support vector regression (SVR), seed points can be detected automatically by regarding the intensity of an image as a surface. Furthermore, an adaptive threshold function is given as the criterion of the homogeneity test instead of a fixed threshold, as used in conventional region-growing algorithms. Our technique can extract small targets without human intervention. We carefully design many experiments to demonstrate its validity in extracting IR small targets.

This paper presents an adaptive control scheme for adaptive optics. Adaptive compensation is needed in many adaptive optics applications because wind velocities and the strength of atmospheric turbulence can change rapidly, rendering classical fixed-gain reconstruction algorithms far from optimal. The paper also presents a method for generating frequency-weighted deformable-mirror modes, which are important for optimal performance of the adaptive control scheme. The performance of the adaptive control scheme is illustrated by simulations of a directed-energy system with a high-energy laser propagating through extended turbulence.

We have developed a spatial demultiplexing/multiplexing algorithm for correcting sinusoidally scanned distorted images. In our approach, the scanned image is demultiplexed into equal spatial slots (strips) perpendicular to the scan direction. Each spatial slot is interpolated through either an oversampling or an undersampling algorithm, depending upon its location. The interpolated spatial slots are multiplexed to reconstruct the corrected image. The implementation of this algorithm shows that, for our 100-pixel-wide test image, depending upon the slot size, it is possible to retrieve at least 99% of the original image, as measured by the recovered energy.

Contrast enhancement is an important issue in image processing, pattern recognition, and computer vision. There are two major kinds of techniques for contrast enhancement: indirect methods and direct methods. The indirect approach is to modify the histogram by changing the original gray levels to new values; it is not efficient and effective because it only stretches the global distribution of the intensities. The basic idea of the direct method is to define a measurement of the contrast and use it to enhance the contrast. Fuzzy logic has been widely applied to image processing since fuzzy set theory can handle the uncertainly, vagueness, and imprecision inherent in the images well. The proposed approach employs the fuzzy entropy principle and fuzzy set theory to automatically determine fuzzy membership functions and uses fuzzy homogeneity to define the contrast and enhance the image. We have conducted experiments on a variety of images, and the results have proved that the proposed method has better performance than the existing approaches.

We propose a novel automatic seeded region growing method based on gradient vector flow (GVF) for color image segmentation. YC_bC_r color space is selected to avoid the high correlation of RGB color space. First, a GVF field is constructed from an edge map of the input image. Then a scaler force field is derived from it by minimizing an energy functional iteratively. From the scalar field, we can select a set of seeds and get an initial segmentation via a straightforward downstream process. Finally, a region adjacency graph–based region merging is applied to merge similar neighboring regions into true results. Experimental results demonstrate that this method is insensitive to noises and efficient to multiple objects segmentation in color images.

This paper presents the timing advantage of implementing a multiple-fan-beam projection technique using optical fiber sensors for a tomography system. To prepare the sensors to be used for this projection, a collimator is not needed, but optical fiber lens termination is crucial. In this research, the fiber optic lens for transmitters is modeled by experimental methods to transmit light at an emission angle of 30 deg. Due to this small emission angle, a multiprojection technique can be implemented without the light overlapping. A multiple-fan-beam projection technique is here defined as one allowing more than one emitter to project light at the same time using the switch-mode fan-beam method. This method can increase the optical sensor's ability for flow visualization. For the 32 pairs of sensors used, the two-projection technique and four-projection technique were investigated. Sixteen sets of projections formed one frame of light emission for the two-projection technique, and eight sets did so for the four-projection technique. Compared to the conventional single-light projection used in the switch-mode fan-beam method, multiple-light projection can achieve a higher data acquisition rate, thus minimizing data loss and producing a more accurate real-time tomographic image. For four projections the data acquisition rate is 609.76 frames/s.

In this paper, we generate a virtual right image corresponding to an input left image by using given RGB texture data and 8-bit gray-scale depth data from a depth camera. First we transform the depth data to disparity data. Then, using this disparity data, we produce a virtual right image. Further, we propose a real-time multiple-view synthesis algorithm using geometric transformations, such as rotation and translation after the stereo image synthesis, and also a fast LUT (look-up table) method for real-time processing through analyzing the correlation between the depth data and the disparity data. As a result, we are able to achieve real-time synthesis of 11-viewpoint stereo images using only RGB texture data and the 8-bit depth information.

A disjoint track matching algorithm is proposed based on major color spectrum histogram representation (MCSHR) matching and post-matching integration algorithms; this algorithm is useful for reconnecting broken tracks due to occlusions and potentially useful for tracking a single object across multiple, disjoint cameras. An incremental MCSHR (IMCSHR) matching algorithm is also proposed to cope with small pose changes occurring along the track. First, an MCSHR is introduced to represent a moving object by its most frequent colors. Then a two-directional (2-D) similarity measurement algorithm based on the most similar major color searching algorithm is proposed to measure the similarity of the two given moving objects by using IMCSHR in a few frames. Last, our track matching algorithm extends the multiframe matching along the object's tracks by a post-matching integration algorithm. Experimental results have shown that the similarity of two tracks from the same moving objects has proven as high as 89 to 97%, while the similarity of two tracks from different moving objects has been kept as low as 14 to 54%. The post-matching integration algorithm has been proven to be able to make track matching more robust and reliable.

The study of the dynamics of an exploratory effort to build knowledge for progressive transmission shows that if initial knowledge about information of interest is large, most exploration to increase the knowledge base can be postponed to higher bit rates, with independence of transmission costs. On the contrary, if proved knowledge is initially small, high exploratory effort must occur at extremely low bit rates so as to increase the inventory of proved knowledge about relevant visual information. From the dynamics of exploratory effort, it follows a hierarchical quantizer partition tree at a near optimal level of exploratory effort until near the end of the progressive transmission without the necessity for any additional exploratory effort. We show an example of the application of this hierarchical quantizer partition tree for progressive transmission of video sequences, where interquantizer prioritization follows a novel hierarchical bit allocation algorithm.

A concave micrograting designed for optical communication applications was fabricated by deep x-ray lithography (DXL). The micrograting has a height of 125 μm, a grating pitch of 3 μm, a total of 2584 lines, and a sidewall root-mean-square surface roughness of 5 nm. The designed operational wavelength range is from 1475 to 1625 nm. This micrograting is embedded inside a mirror-planar waveguide to form a spectrometer chip. The Rowland-circle grating mounting scheme is used for the spectral detection. The calculated diffraction efficiency of the third-order diffraction reaches 65% when Au is coated on the grating surface and the blaze angle is suitably chosen. The measured spectral width is 1.1 nm, which is in very good agreement with the calculated result of 0.9 nm. This chip-based grating device can be used as an ultracompact spectrometer or an ultracompact wavelength-division multiplexer in optical communications. Based on this work, our DXL technique can be further developed into an x-ray LIGA method for the mass production of such chip-based spectrometers.