This PDF file contains the editorial “Editorial: Engineering a Garden” for OE Vol. 44 Issue 06

A fast disparity estimation algorithm based on a pixel-based approach for intermediate view reconstruction (IVR) is proposed. The proposed algorithm uses the matching property of stereo imaging: in stereo images, the disparity vector of a pixel is located between those of previous and subsequent pixels. According to the experiments, the proposed algorithm can reduce the computational complexity by about 8 times and achieves competitive or slightly better peak signal-to-noise ratio (PSNR) in comparison with the pixel-based full search approach. The algorithm is proven to be effective in the implementation of the real-time disparity estimation processor for arbitrary 720×480 stereo images.

A 32-channel 50-GHz spaced arrayed-waveguide grating with our innovative configuration has been designed and fabricated. The performance of the device has been fully tested by using a tunable laser light source, optical power meter, and polarization controller. The insertion loss (IS) of the device is 4.2~7.4 dB. The crosstalk is about –28 dB. The IS uniformity is less than 3.2 dB. With our configuration, the performance of the device has been enhanced effectively and the difficulty in alignment process has been decreased obviously.

Fiber Bragg gratings (FBG) were manufactured during the fiber drawing process [draw tower grating (DTG)] with excellent reflectivity values. This was done in the region of 1550 nm by single pulses of a 248-nm excimer laser applied during the fiber drawing process of single mode fibers. An improved setup for the writing process and special photosensitive fibers enable the manufacture of type I DTG arrays with a reflectivity of up to 40% and type II DTGs with a reflectivity near 100%. Details of the setup and results of the DTG arrays and DTGs of type II are reported.

A new bidirectional pumped configuration for an L-band erbium-doped superfluorescent fiber source is demonstrated. Data are presented showing that with this configuration, the mean wavelength variation with the pump power can be reduced to zero by optimizing the fiber length and the pumping ratio of forward to total pump power.

We propose and experimentally demonstrate a novel and simple tunable passively mode-locked fiber ring laser. A polarization-dependent Mach-Zehnder amplitude modulator is used to replace the polarizer inside the cavity. When the modulator is biased at different voltages and without any rf input signal, we obtain a stable soliton pulse train with repetition rates from 50 to 300 GHz.

A new structure for diaphragm-based extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensors is presented. This structure introduces a through hole in a conventional diaphragm-based EFPI sensor and significantly reduces the effect of operating point drift due to the background pressure and fluctuations. This structure also potentially has high temperature stability.

We demonstrate tunable single- and dual-wavelength fiber ring lasers using a compact Er-Yb doped waveguide amplifier. In the single-wavelength operation, a signal-to-noise ratio higher than 63 dB and an output power maintaining around 11 dBm in the operation range over 50 nm (from 1529.1 to 1579.43 nm) are achieved. In the dual-wavelength operation, lasing wavelengths with wavelength separation from 51.73 to 6.2 nm are demonstrated.

A 1.60-µm laser diode and electroabsorption modulator monolithically integrated with a dual-waveguide spot-size converter output for low-loss coupling to cleaved single-mode optical fiber is demonstrated. The devices emit in a single transverse and quasi-single longitudinal mode with a side mode suppression ratio of 25.6 dB. These devices exhibit a 3-dB modulation bandwidth of 16.0 GHz, and modulator extinction ratios of 16.2 dB dc. The beam divergence angle is about 7.3×10.6 deg, resulting in 3.0-dB coupling loss with cleaved single-mode optical fiber.

We present an upstream transmission method independent of temperature characteristics of the remote node (RN) in a WDM-PON. This method employs a self-injection locked Fabry-Perot laser diode (F-P LD) for upstream transmission in the optical network unit (ONU). Using this method, the sidemodes of the F-P LD are suppressed, and the F-P LD is matched to the center wavelength of the wavelength distributor/combiner placed at the RN. The experimental results confirm that bidirectional error-free transmission at 1.25/10 Gbit/s could be achieved.

A new algorithm for the rate control of videos considering the sensitivity of the human visual system (HVS) is presented. The method adopts the three-step structure of MPEG-2 Test Model 5 (TM5) rate control, while a new measure for the macroblock (MB) activity based on spatiotemporal sensitivity is introduced. Experimental results show that the proposed activity measure outperforms the spatial activity of TM5 in picture quality.

The axial intensity distribution and focal depth of an apodized focusing optical system are theoretically investigated with two kinds of incident light fields: a uniform-intensity-distribution beam and a Gaussian beam. Both a low-numerical-aperture and a high-numerical-aperture optical system are considered. Numerical results show that the depth of focus can be adjusted by changing the geometrical parameters and transmissivity of the apodizer in the focusing optical system. When a Gaussian beam is employed as the incident beam, the waist width also affects the depth of focus. The tunable range of the focal depth is very considerable.

For successful assembly of deformable parts, information about their deformation as well as possible misalignments between the holes and their respective mating parts are essential. Such information can be mainly acquired from visual sensors, and mirrors can be incorporated with a camera to obtain the necessary three-dimensional information by stereo vision. In case of visual sensing systems with multiple mirrors, systematic errors need to be reduced by the system calibration and the mirror position adjustment in order to enhance system measurement accuracy. In this paper, a self-imaging method is presented to adjust and calibrate the mirror position of a visual sensing system designed to measure the three-dimensional information in deformable peg-in-hole tasks. It is composed of a CCD camera and a series of mirrors including two pyramidal mirrors. The measurement accuracy of the system is discussed as well. The ideal designed accuracy can be obtained from the design specification, and the actual accuracy can be obtained from experimental results. The designed resolution of the system is about 0.2 mm per pixel of the camera, but actual measurement error is about three times larger than the theoretically possible error according to the designed resolution.

A theoretical investigation of the effects of imaging a patterned rough surface through focus is performed, and the statistics of the image plane irradiance, as well as those of the image pattern printed in a threshold-type photoresist, are investigated. It is demonstrated that the line edge roughness in the printed image increases substantially as the image plane is moved out of focus, for both fully and partially coherent optical systems. Furthermore, the increase in line edge roughness occurs in what is considered to be an otherwise acceptable depth of focus for an ideal system.

A thin layer of SU-8 submicron pattern produced by holographic lithography is used as the dry etch mask in a chemically assisted ion beam etching (CAIBE) system. The effect of the chlorine gas flow rate on etched sidewalls is investigated; by matching the lateral etch rate and the deposition rate, etching selectivity of up to 7:1 is achieved, rendering smooth vertical sidewalls and damage-free upper portions for the etched structure.

We present a new algorithm to determine, quickly and accurately, the best-in-focus image of biological particles. The algorithm is based on a one-dimensional Fourier transform and on the Pearson correlation for automated microscopes along the Z axis. We captured a set of several images at different Z distances from a biological sample. The algorithm uses the Fourier transform to obtain and extract the image frequency content of a vector pattern previously specified to be sought in each captured image; comparing these frequency vectors with the frequency vector of a reference image (usually the first image that we capture or the most out-of-focus image), we find the best-in-focus image via the Pearson correlation. Numerical experimental results show the algorithm has a fast response for finding the best-in-focus image among the captured images, compared with related autofocus techniques presented in the past. The algorithm can be implemented in real-time systems with fast response, accuracy, and robustness; it can be used to get focused images in bright and dark fields; and it offers the prospect of being extended to include fusion techniques to construct multifocus final images.

We propose a distance measuring system based on lateral shearing interferometer (LSI) with extended range of measurement and improved resolution. The sensor is based on a wedge-shaped plate LSI and due to the presence of tilt, a finite number of fringes parallel to the direction of shear appear and hence significant spatial carrier frequency is generated at the focus position. On varying the distance of the object surface from the focus position, the orientation, fractional and integer order, and the width of the interference fringes change. It is shown that the orientation of the fringes is the most sensitive parameter, by means of which one can detect small changes in distance. The Fourier transform method for fringe analysis is used, and from the position of the maxima of the first-order Fourier spectrum the orientation of the fringes and hence the distance is measured. Experimental results of distance measurement by changing the focal length of the lens are presented. A large range of measurement without any fringe ambiguity problem can be achieved using the system.

Visible/long-wave infrared (LWIR) beamsplitter optical elements are designed, fabricated, and tested to enable implementation of a single common-aperture dual-spectral-mode imaging sensor system. The coating design is compatible with both germanium and low-cost electronic-grade silicon wafer substrates. Multispectral transmission and reflection efficiencies averaging over 90% are measured over both the visible to near IR (NIR) and the LWIR spectral regions, in agreement with theoretical models. The coating design uses commercial-off-the-shelf (COTS) coating materials known to exhibit excellent mechanical and environmental stability for performance reliability and extended operational lifetime.

A novel high-average-power pulsed CO₂ laser with a unique electrode structure is presented. The operation of a 5-kW transverse-flow CO₂ laser with the preionized pulse-train switched technique results in pulsation of the laser power, and the average laser power is about 5 kW. The characteristic of this technique is switching the preionized pulses into pulse trains so as to use the small preionized power (hundreds of watts) to control the large main-discharge power (tens of kilowatts). By this means, the cost and the complexity of the power supply are greatly reduced. The welding of LF2, LF21, LD2, and LY12 aluminum alloy plates has been successfully achieved using this laser.

We demonstrate efficient lasing of bulk diode-pumped Er³+:Yb³+:YAG at 1.645 µm. The material is transversely pumped using three quasi-cw 960-nm laser diode arrays in a simple arrangement. In the free-running mode of operation, an output pulse energy of 79 mJ is obtained at 4.7 J of incident optical pump energy. The lasing threshold lies in the range 1.0 to 1.9 J in long-pulse operation, depending on pumping conditions, and optical slope efficiencies of 2.2% to 3.4% were measured with respect to the incident pump energy. Furthermore, initial Q-switching experiments with a Co:MALO saturable absorber yielded pulses of 1.7-mJ energy and 340-ns FWHM duration. As the reported laser setup also has an uncomplicated and compact design, it represents a good crystalline rare-earth candidate system with superior material qualities to compete against the established glass-host materials in the eye-safe wavelength range.

We report an intracavity ring laser constructed using two parallel directional fiber couplers that generates up to sixth-order cascaded Stokes. Pumping with 1117 nm results in a Raman fiber laser operating at 1572 nm. Using 4.2-W pump power and a fiber Bragg grating at 1117 nm to reflect the residual pump, we obtain an output power of 0.65 W, and hence near 15% conversion efficiency. The linewidths of the dual-coupler laser are significantly narrower than those of the single-coupler laser. This enhanced wavelength selectivity is attributed to the significant increase in the contrast or the finesse of compound ring resonators constructed with two parallel couplers.

We present an axisymmetric-fold combination laser resonator. For a laser with the resonator, it can give a strong output, a good light beam, and a small device volume. The energy flux of the beam is high and the diameter is small in the near field; it diverges with a small angle, but transforming the beam from a divergent beam into a parallel or convergent beam is convenient. The resonator is suitable for various kinds of lasers.

A system to generate wavelength-tunable optical short pulses with a constant repetition frequency and pulse width by a gain-switched Fabry-Pérot laser diode (FPLD) in a self-injection scheme is demonstrated. A variable optical delay line is used to control the self-injection scheme to maintain a constant repetition frequency and pulse width at different wavelengths. The optical sidemode suppression ratio (SMSR) of this system is better than 33 dB over the wavelength-tunable range of 33 nm.

We demonstrate a highly stable, all-polarization-maintaining fiber semiconductor ring laser source. It uses a semiconductor optical amplifier (SOA) to provide both gain and gain modulation from an external 5-GHz optical pulse train. The laser source generates 3.5-ps pulses up to a 50-GHz repetition rate with negligible amplitude pattern.

We report on the design and experimental evaluation of the hybrid fiber Bragg grating (FBG) piezoelectric voltage sensor developed specifically for remote monitoring of electrical submersible pump (ESP) motors. Unlike a previously reported transducer based on a single piezoelectric element, the voltage rating of the presented device could be as low as 500 V due to the use of a multilayer piezoelectric stack as the primary voltage-to-strain transducer. This enables the use of such sensors across a wider range of ESP applications, which often have subkilovolt voltage ratings. In addition to the design details, we present details of the full characterization of the device, including the hysteresis and temperature-dependence characteristics and discuss ways of eliminating or reducing these effects. We also demonstrate that the sensor can be used to simultaneously measure voltage and temperature.

The combination of the effective index method and the transfer matrix method is adopted to calculate the indices of quasi-TE and quasi-TM modes in a UV-written channel waveguide, and the difference between the indices is used to characterize its birefringence. The dimensions, the ratio of width to thickness, the original index of the core layer, the index of the cladding, and the index profile are all taken into account. The simulation results indicate that the birefringence decreases with increasing dimensions, ratio of width to thickness, and indices of the cladding; on the contrary, increases of the original index of the core layer and of the vertical index gradient intensified the birefringence.

A thermo-optic variable optical attenuator module composed of a silicon-on-insulator attenuator chip and driving circuit was designed and fabricated. The module exhibited a maximum attenuation of 21.8 dB and a response time of 10 µs.

The operation of a semiconductor-optical-amplifier-assisted Sagnac recirculating shift register with an inverter is studied theoretically and analyzed using a numerical model developed for this purpose. The impact of critical operational parameters, such as the SOA small-signal gain and carrier lifetime, the controlling pulses' energy and width, and the Sagnac loop asymmetry, on the switching energy and contrast ratio metrics is thoroughly investigated. The performance of the shift register is first evaluated at 10 GHz by comparing the simulated results against experimental ones, which reveals good agreement and proves the validity of the model. The model is then exploited to derive the optimum operating conditions in terms of the critical parameters that render feasible the extension of the storage capability to 20 GHz. The analysis demonstrates that the major limiting factor in achieving this goal is the SOA carrier lifetime, which must be significantly reduced. Since this requirement cannot be satisfied by simply varying the SOA bias current, either efficient gain recovery acceleration techniques must be used (at the cost of increased complexity), or the faster response and ultrahigh-speed switching potential of quantum-dot SOAs can be exploited.

A theoretical analysis of the light absorption and gain mechanisms in a Cd₃P₂ Semiconductor Cylinder Fiber is presented. The results of these calculations are in good agreement with previously published experimental data. Cd₃P₂ has two direct energy gaps, which both influence the gain mechanism. Pump light can be used to reduce the absorption. Stronger pump light that generates more charge carriers will produce net gain (gain above absorption compensation). The fiber exhibits gain over a very wide light wavelength bandwidth.

Optical soliton propagation through an optical fiber is a well-established phenomenon in digital optical communication. This propagation can be exploited to secure many advantages in communication because of the unattenuated, unchirped, and undistorted Gaussian optical pulse propagated through the fiber. Here we propose a completely new scheme for controlling the power shape function of a Gaussian optical pulse propagated through an optical fiber in the form of soliton, leading to some new characteristics in connection with such propagation. To exploit this possibility an electro-optic modulator is used on the pulse before its introduction into the fiber.

A multiresolution time-domain (MRTD) method based on Daubechies scaling functions is proposed for the time-domain analysis of planar optical waveguide devices. The anisotropic perfectly matched layer absorbing boundary condition is implemented for the MRTD method. The proposed scheme is used to model the parallel-slab directional coupler, and the simulation results are in good accord with the analytical solutions. Compared with the standard finite-difference time-domain method, this scheme can save considerably computer resources without loss of accuracy.

We propose a simple all-optical technique for digital encoding of ASCII. The method accommodates a digital encoding system by using the optical tree architecture and a nonlinear-material-based optical switching operation.

Two novel read-only memory (ROM) disks, one with an AgO_x mask layer and the other with an AgInSbTe mask layer, are proposed and studied. The AgO_x and the AgInSbTe films sputtered on the premastered substrates with pit depths of 50 nm and pit lengths (space) of 380 nm are studied by atomic force microscopy. Disk readout measurement is carried out using a dynamic setup with a laser wavelength of 632.8 nm and an object lens numerical aperture (NA) of 0.40. Results show that the superresolution effect happens only at a suitable oxygen flow ratio for the AgO_x ROM disk. The best superresolution readout effect is achieved at an oxygen flow ratio of 0.5 with the smoothest film surface. Compared with the AgO_x ROM disk, the AgInSbTe ROM disk has a much smoother film surface and better superresolution effect. A carrier-to-noise ratio (CNR) of above 40 dB can be obtained at an appropriate readout power and readout velocity. The readout CNR of both the AgO_x and AgInSbTe ROM disks have a nonlinear dependence on the readout power. The superresolution readout mechanisms for these ROM disks are analyzed and compared as well.

Numerical simulations of the influence of the phase step miscalibration and average intensity changes between the registered frames on the time-averaged interferogram contrast calculated using the temporal phase-shifting (TPS) method are presented. The amplitude of sinusoidal vibration studied by the time-averaged method is encoded in the interferogram contrast or intensity modulation described by the zero-order Bessel function. The properties of the TPS method used for contrast determination are established. Experimental studies of vibration mode patterns of silicon microelements with specular reflection surfaces provide corroboration of theoretical and numerical findings.

Two designs for antenna-coupled Ni-NiO-Ni diodes are fabricated and tested for dual-band detection in the millimeter-wave (MMW), 94-GHz, and infrared (IR), 28.3-THz, frequencies. The detector noise, antenna receiving properties, and noise equivalent power (NEP) are measured. The simultaneous dual-band response is verified.

We describe the development of an analog very large scale integration (AVLSI) system for perceiving depth of a stationary object, termed the depth through motion parallax (DTMP) system. The system consists of an AVLSI smart focal plane array and an optical lens, with a laser system for the object. The DTMP integrated circuit is implemented using the AMI Semiconductor 1.5-µm process available through the MOSIS integrated circuit fabrication service. The DTMP chip and the lens are mounted on a single motion-controlled stage to mimic the human head and eye. The object is mounted on a different motion stage and is manually moved to different depths with respect to the lens. We report experimental results obtained for depth perception with the head being stationary and the object moving with a constant velocity that is geometrically equivalent to the object being stationary and the head moving with a constant velocity. Our results show that the transit time across the DTMP chip, which is equivalent to the perceived velocity, can be used to determine the depth of an object, and uses less than 2 mW of average power.

A unified, simplified, and concise overview of spectral target detection algorithms for hyperspectral imaging applications is presented. We focus on detection algorithms derived using established statistical techniques and whose performance is predictable under reasonable assumptions about hyperspectral imaging data. The emphasis on a signal processing perspective enables us to better understand the strengths and limitations of each algorithm, avoid unrealistic performance expectations, and apply an algorithm properly and sensibly.

Although side-match vector quantization (SMVQ) and its variants have been proposed to reduce the bit rate of coding images, the coding quality is decreased by it. The reason is that when a block is encoded in SMVQ, the side-match method uses only two neighboring blocks, (no edge information is available in the other two neighboring blocks) to predict the state of the codebook. We propose a new variable-rate finite state vector quantizer (VRFSVQ) to encode the blocks with a variable rate according to both the coding quality and the bit rate. The VRFSVQ can preencode all the blocks, allowing each block to employ more than two neighboring blocks to yield the state codebook. Furthermore, whereas users of SMVQ must specify the size of the state codebook before applying the side-match method to yield the state codebook, in the VRFSVQ the users do not need to specify the size of the state codebook for each encoding block. Experimental results indicate that the VRFSVQ has a high peak SNR and low bit rate for image coding.

Recently, wavelet analysis has been used to denoise a digital image corrupted by noise in the acquisition step. Because of the multiscale decompositions (multiresolution) and translation parameter (locality in space), in addition to the scale parameter of the wavelet there are two types of correlations that can be used to detect edges. Many previous works have exploited the intrascale or interscale dependences alone to denoise the image. In this paper, a denoising method that combines the intrascale and interscale correlations simultaneously is proposed. By manipulation of the wavelet coefficients in successive bands, this noise model is investigated exhaustively and estimated as the well-known Gaussian distribution. With the investigated noise distribution, a new denoising method is proposed. Experimental results show the superiority of the proposed method to the interscale or intrascale method according to objective and subjective criteria.

The theoretical foundation is developed for a new technique to determine displacements with subpixel accuracy at each pixel location in a digital image of a deformed object using digital image correlation (DIC). This technique, known as pointwise DIC, is evaluated using ideal sinusoidal images for the cases of rigid body translation, extensional strain, and rigid body rotation. Displacement fields obtained using objective correlation functions with and without intensity gradients are compared. Both bilinear and bicubic interpolation schemes are investigated for reconstructing the subpixel intensity and intensity gradient values in undeformed and deformed images. The effects of transforming the Eulerian description of the intensity gradients in the deformed images to the Lagrangian description in the undeformed images are also investigated. The optimal correlation value and the calculated displacement fields of the two interpolation schemes are compared. Theoretical results demonstrate that pointwise DIC can accurately determine displacement fields. To demonstrate the advantages of pointwise DIC over conventional DIC techniques, an ideal image simulating a twinning deformation is correlated, indicating the pointwise technique is up to two orders of magnitude more accurate at determining discontinuous displacements than the conventional technique. Experiments are also conducted on a polycarbonate dogbone specimen that validate pointwise DIC on real images and determine the inherent accuracy in the digital image acquisition.

In the absence of a priori knowledge about regions of interest, does dysfunctional behavior in the subband pyramid lead to the emergence of a region-based approach to image transmission as complexity grows? A model of image transmission that links simplification of information and time to produce a transmission plan to the bit-rate cost of the transmission, and where the decoded output is affected negatively by those factors that reduce the quality of the transmission plan and delay its preparation, answers the question in two steps. First, we characterize the variables (degrees of simplification and subordination) through which we expect to control, at any truncation time, the optimum transmission system. We observe that transform-domain coefficients exhibit self-seeking behavior if errors that result from the transmission plan increase as the distance of the coefficient from the top of the hierarchy grows. Then we use the degree of detail that arrives at the central control in any system of progressive transmission to derive conditions under which the likelihood of emergence of a region-based approach to progressive transmission grows with the increase of complexity of the picture. We find that the presence of self-seeking coefficients leads to a higher likelihood of emergence of a region-based approach as complexity rises. On a data set composed of 100 standard gray-scale test images, 26% of the test images exhibit self-seeking behavior, from very low bit rates, using the state of the art codec based on set partitioning in hierarchical trees.

The performance of target detection and tracking algorithms generally depends on the signature, clutter, and noise that are usually present in the input scene. To evaluate the effectiveness of a given algorithm, it is necessary to develop performance metrics based on the input plane as well as output plane information. We develop two performance metrics for assessing the effects of input plane data on the performance of detection and tracking algorithms by identifying three regions of operation—excellent, average, and risky intervals. To evaluate the performance of a given algorithm based on the output plane information, we utilize several metrics that use primarily correlation peak intensity and clutter information. Since the fringe-adjusted joint transform correlation (JTC) was found to yield better correlation output compared to alternate JTC algorithms, we investigate the performance of two fringe-adjusted JTC (FJTC)-based detection and tracking algorithms using several metrics involving the correlation peak sharpness, signal-to-noise ratio, and distortion invariance. The aforementioned input and output plane metrics are used to evaluate the results for both single/multiple target detection and tracking algorithms using real life forward-looking infrared (FLIR) video sequences.

A watermarking algorithm operated in the wavelet transform domain is proposed. For the purpose of security and robustness, we generate a watermark sequence by selectively modifying the middle-frequency parts of images. Meanwhile, we also employ the masking characteristics of the human visual system (HVS) to ensure the watermark invisibility. The watermark data are detected using the embedding position after the wavelet decomposition of the watermarked image. The experimental results show that the proposed scheme is superior to quantization-based methods in terms of transparency, robustness, and computation complexity.

We propose a new method of digital watermarking with the double binary optical phase encoding technique. The iterative Fourier transform algorithm (IFTA) is used to generate the binary phase structures. The combination of two binary phase structures, in which one is used to encode the hidden image and the other is used as the encryption phase key, is inserted as a watermark into the host image. The effects of phase levels of binary phase holograms on the quality of extracted image are analyzed, and the results show that the 2/2 phase level combination is a better scheme for watermarking than other multiple combinations. We also present the principle of the encrypting key. Both analysis and experimental results illustrate that this technique is of high security and robust against the printing and scanning process.

We propose a reformed method that utilizes the motion vectors (MVs) in an MPEG sequence as the motion depicter for motion analysis and representation of video contents. The MVs are converted to a uniform MV set, independent of the frame type and the direction of prediction, and then used as motion depicters in each frame. To obtain such a uniform MV set, a new motion analysis method using bidirectional prediction-independent framework is proposed. Generally, it is impossible to directly compare an I frame without MV to others such as B or P frames. But, this approach enables a frame-type-independent representation that normalizes temporal features including frame type, macroblock (MB) encoding, and MVs. Experimental results show that our method has good performance and high validity. Compared with a full-decoding method, the average of the processing time in our method is reduced about 55%, because our method is directly processed on the MPEG bit stream after variable length code (VLC) decoding. Average of the effective number of the normalized MVs in the proposed algorithm is increased about 25% than that of the conventional method.

We obtain a novel analytical derivation for distortion-related constraints in a neural network- (NN)-based automatic target recognition (ATR) system. We obtain two types of constraints for a realistic ATR system implementation involving 4-f correlator architecture. The first constraint determines the relative size between the input objects and input correlation filters. The second constraint dictates the limits on amount of rotation, translation, and scale of input objects for system implementation. We exploit these constraints in recognition of targets varying in rotation, translation, scale, occlusion, and the combination of all of these distortions using a learning vector quantization (LVQ) NN. We present the simulation verification of the constraints using both the gray-scale images and Defense Advanced Research Projects Agency's (DARPA's) Moving and Stationary Target Recognition (MSTAR) synthetic aperture radar (SAR) images with different depression and pose angles.

We differentiate surfaces with different properties with simple low-cost IR emitters and detectors in a location-invariant manner. The intensity readings obtained with such sensors are highly dependent on the location and properties of the surface, which complicates the differentiation and localization process. Our approach, which models IR intensity scans parametrically, can distinguish different surfaces independent of their positions. Once the surface type is identified, its position (r,θ) can also be estimated. The method is verified experimentally with wood; Styrofoam packaging material; white painted matte wall; white and black cloth; and white, brown, and violet paper. A correct differentiation rate of 100% is achieved for six surfaces, and the surfaces are localized within absolute range and azimuth errors of 0.2 cm and 1.1 deg, respectively. The differentiation rate decreases to 86% for seven surfaces and to 73% for eight surfaces. The method demonstrated shows that simple IR sensors, when coupled with appropriate signal processing, can be used to recognize different types of surfaces in a location-invariant manner.

The coupling of a laser focused into a water microjet is studied. Using a high-power laser, the light guided in the jet is used to process various materials. To explain the observed ablation patterns, the propagation of a low-power and highly coherent laser beam coupled into a laminar water jet is studied. The light of a He-Ne laser (5 mW) is focused into the water jet, which behaves as a multimode waveguide. The distribution of the light intensity in the jet impinging on a glass plate cutting the jet perpendicularly to its propagation direction is recorded for various laser coupling conditions. The influence of the jet diameter, as well as the influence of the depth of focus of the incident beam and its position with respect to the center of the jet is studied. A nearly homogeneous grain size was observed over the whole jet cross section. The characteristic grain size was then compared with predictions from standard multimode fiber theory. Finally, it is confirmed that the structures resulting from material ablation using the laser-microjet technology when coupling Q-switched Nd:YAG (λ=1064 and 355 nm) are closely related to the predicted light intensity distributions. Furthermore, recommendations are made concerning the coupling conditions for optimizing the laser processing applications.

Diffractive wavefront control with programmable optically efficient modulo λ gratings was previously demonstrated as a means of extending the capabilities of a telescope system by compensating large aberrations associated with variations in object range and field angle within the telescope's field of regard. Inherent in diffraction phenomenon, however, are wavelength dependences that impose limitations on operating spectral bandwidths. This paper builds on past work integrating a programmable diffractive element of large pixel count with a telescope system. We present a theoretical evaluation of the wavelength-dependent performance characteristics of a modulo λ diffractive aberration compensator and experimental demonstrations of wavelength-tunable and extended spectral bandwidth operation. Near-diffraction-limited-resolution imaging is demonstrated within the spectral operating limits imposed by diffraction theory.