This PDF file contains the editorial “Editorial: Life in the Dark Ages” for OE Vol. 44 Issue 10

A strategy to escape from poor local minima by switching merit functions during local optimization is discussed. As a switching partner, we define a new auxiliary merit function, which also tends to zero for ideal systems, but differs significantly from traditional merit functions. The examples include high-dimensional optimization problems.

We demonstrate a tunable microwave-photonic notch filter based on a variable polarization beamsplitter, a Hi-Bi coupler, and a variable time delay line. The configuration is free from the problems of optically coherent interference and chromatic dispersion. An expression for the filter transfer function is derived. Measured results match the calculated results and show a notch rejection greater than 35 dB. The notch frequency is continuously tunable by adjusting the time delay value. The scheme can operate over a wide range of optical carrier frequencies.

The properties of a paraboloid made of dielectric material and truncated from the focal plane are studied. In addition, the focusing of light emitted by astigmatic diode lasers with a truncated paraboloid is discussed. Finally, ray-tracing calculations are presented for a high-numerical-aperture truncated paraboloid used for focusing light emitted by a large number of diode lasers in an axially symmetric structure.

The parasitic background signal produced by gas detectors using a Fabry-Pérot interferometer (FPI) as a modulator is shown to be very sensitive to the infrared bandpass filter characteristics. This parasitic signal is generally the feature limiting the sensitivity of such devices. We review this problem, and provide a general approach to filter choice that minimizes the background amplitude for this kind of detection system. It is shown that in general filters with very abrupt transitions from the stop to passband are in fact undesirable, and fortuitously the optimum choice of filter leads to easily realized, low-cost designs.

The paper describes a technique, based on quaternion algebra, to implement the control loop for the inertial stabilization of the line of sight of an optical system. The paper includes a theoretical description of the method and the adopted mathematical tools, thus indicating the meaning of the symbols used. Particular attention is paid to the specific use made of quaternions in the algorithms. The parameters of the control loop, used in the verification of the technique, are detailed in order to provide a better understanding of the problem. The control loop has been extensively tested in simulation and in practice, and it has provided good and appropriate results.

One feature of systems with sparse optical aperture is the possible existence of zero-value regions of the optical transfer function. In using fast-convergent gradient methods for nonlinear constrained optimization with criteria based on the optical transfer function or the modulation transfer function, the gradient of the minimized function can also contain zero-value regions. Such situations can result in a suspension of the calculation if an intermediate solution falls into such a region. We show that, using gradient methods, it is possible to avoid this calculation problem if we redefine the subaperture step pupil functions--in particular, approximate them by continuously differentiable functions having no zero-value regions. This is demonstrated on examples of apertures consisting of circular and annular subapertures. This approach can be used for both types of multiaperture optical telescopes, the Michelson and Fizeau, and for both space and earth science missions.

Programmable diffractive optics (PDO) based on liquid-crystal (LC) technology has been demonstrated as a wavelength-tunable technology for compensating large aberrations over limited instantaneous spectral bandwidths. Acousto-optic tunable filters (AOTFs) based on acousto-optic Bragg diffraction have been demonstrated as a wavelength-tunable technology for selecting narrow spectral bands from white light with high rejection ratios. These technologies are integrated into a telescope system that includes a conventional primary mirror utilized off axis with more than 40 waves of aberration to view a white-light-illuminated object bar chart. A high-resolution LC PDO, situated in a pupil plane, compensates for the large primary mirror aberration. The AOTF, operating in an image plane, rejects light outside a 2-nm spectral band centered about the wavelength at which the modulo λ phase profile of the PDO is defined. Wavelength-tunable narrowband imaging is achieved by synchronously tuning the PDO and AOTF over a 100-nm spectral range. Near-diffraction-limited image quality is demonstrated.

It is well known that ion-assisted deposition (IAD) using a plasma source improves the optical and physical characteristics of optical thin films. A broad-beam cold-cathode plasma source was used in this study. The versatile ion source selected can easily be retrofitted into existing deposition chambers or new installations. This paper discusses characterization of the ions produced by the plasma source and analyzes the properties of thin films produced using the plasma source for IAD. Ion energy measurements were made using an ion energy analyzer for the determination of ion energy distribution functions (IEDFs). IEDFs were measured for three gases; argon, oxygen, and nitrogen. The ion characteristics in oxygen are focused on. The effect of pressure and drive current on the IEDFs of oxygen ions is discussed. Mean ion energies of oxygen as a function of pressure, drive voltage, and drive current were calculated. Since the density and quality of films are related to the ion current density during deposition, the effects of drive voltage, pressure, and the pumping speed of the system are discussed. Characteristics of TiO₂ and Ta₂O₅ films deposited on silicon wafers and microscope slides were investigated. The conditions for moisture stability of these films were analyzed.

A simple and intelligent technique of reducing the zero-order diffraction in an optical spectrographic processor is discussed and the corresponding nonbias optical architecture, by which spectrograms can indeed be obtained, is proposed. Reduction of zero-order diffraction in a Fourier optical system arises from the removal of the dc bias, which is usually needed when a conventional optical spectrographic processor is utilized. We have shown that discrimination sensitivity of the optical spectrograms is significantly enhanced and the dynamic range (DR) requirement for the spectrogram capturing device is also notably reduced due to the removal of the dc bias. In addition, energy utilization efficiency in the optical signal processing is drastically improved by our nonbias architecture. Simulated demonstration is provided.

In part I of this study a laser-based system for automatic measurement of spur gears' tooth thickness and pitch was introduced. The developed system provides an inaccuracy value on the order of 5 µm, and the measurement time, for all gear teeth, was just about 1 min. In this part the experimental work is further extended to measure the tooth flank profile of spur gears. Flank profile is one of the most important factors that affect gear performance. In gear meshing, motion is transferred through contact along gear flanks. Deviations in flank profile due to errors in manufacturing or nonuniform wear result in variations in gear movement. Measurement of the flank profile can help in adjusting the gear manufacturing process, control the quality of manufactured gears, and monitor the wear of gears during action. The proposed flank profile measurement system is based on the principle of optical triangulation. The flank profile measurement setup is integrated with that of the tooth thickness and pitch, and hence tooth thickness, pitch, and profile measurements are performed simultaneously, and the measurement time for the three parameters for all gear teeth remains less than 1 min. Software is developed to graph the actual tooth profile and evaluate its deviation from nominal shape. The flank profiles measured using the developed system are in good agreement with those obtained from a well-established measurement method.

A stable and wavelength-tunable C- plus L-band fiber double-ring laser, which uses a two-stage hybrid amplifier with a semiconductor optical amplifier and an erbium-doped fiber amplifier, has been proposed and experimentally demonstrated. Based on the double-ring configuration, the proposed fiber ring laser exhibits more stable output wavelengths and powers than the single-ring laser. A wide tunable range of 1540 to 1620 nm, a side-mode suppression ratio (SMSR) of <31.2 dB/0.05 nm over a wide tuning range from 1550 to 1612 nm, and an output power of <2 dBm over the operation range of 1546 to 1608 nm have been achieved.

The effect of intracavity apertures and distributed Bragg reflectors (DBRs) on transverse-mode discrimination in vertical-cavity surface-emitting lasers is investigated theoretically. The effects of aperture shape and size as well as the stop-band width of the DBRs are examined with the goal of optimizing the mode discrimination for better lasing stability and higher single-mode power. It is found that decreasing the width of the DBRs' stop band, by means of controlling the material composition and number of layer pairs, increases significantly the optimum aperture size and hence the single-mode output power.

We have proposed and experimentally demonstrated a stabilized and tunable S-band erbium-doped fiber ring laser by using a Fabry-Perot laser diode (FPLD) and a fiber Fabry-Perot filter inside the ring cavity. Due to the bandwidth limitation of the FPLD, the effective operating range of the proposed laser is confined to 1490.28 to 1521.22 nm with a tuning step of 0.08 nm. A side-mode suppression ratio of <39.1 dB at 0.05 nm and an output power of <0.4 dBm can be achieved while this laser is tuned from 1490.28 to 1510.27 nm. Zero output wavelength variation and output power fluctuation ≤ 0.03 dB have also been obtained.

The influence of optical feedback on the longitudinal mode stability of microchip Nd:YAG lasers is demonstrated. Under optical feedback, the longitudinal mode output of microchip lasers relies strongly on the external cavity length, and mode suppression can be achieved. The intensity modulation waveform varies at different external cavity lengths. At higher feedback levels, the laser flips between orthogonal polarizations. Three important factors determining the influence of optical feedback are summarized, which are the external cavity length, longitudinal mode competition, and the external reflectivity.

We describe a fiber optic extrinsic Fabry-Perot interferometer (EFPI) based temperature sensor that incorporates a pressure isolation fixture. The sensor has high temperature sensitivity and low pressure-induced crosstalk. The detailed analysis and discussion of the sensor design, the signal demodulation algorithm, and the sensor fabrication as well as the sensor performance are presented.

This work presents an experimental demonstration of an optical joint transform correlator based on the wavelet subband filter for texture pattern recognition. The optical wavelet subband filter is implemented using 4f filtering architecture and utilized to extract the texture features of fingerprints under noisy environments through frequency- and orientation-selective properties. The filtered texture features with noise reduction are applied to optimize recognition via joint transform correlation. Experimental results show that the optical wavelet subband filter enhances the significant texture features from corrupted fingerprints and increases the pattern discrimination of the joint transform correlator.

An optical beamformer capable of controlling a phased array antenna in receive/transmit mode for multiple simultaneous independent rf beams is proposed. The processor can be programmed to sweep the antenna aperture following an independent angular sequence for each rf beam. A two-beam two-channel version of the beamformer has been experimentally demonstrated. The optical beamformer processes two rf beams and it is based on a ternary array of three delay lines. Measurements are performed for both receive and transmit modes and for rf signals between 0.5 and 1.5 GHz. We present beampattern results showing that two independent beams can be steered simultaneously. In the transmit mode both rf beams are characterized for a broadside target position. In the receive mode the beamformer performance is characterized by detecting two rf beams independently.

A simple and efficient technique based on stimulated Brillouin scattering is proposed to reduce RF loss in radio-over-fiber systems. The modulation depth and RF signal gain increase with the power of the input modulated signal. A modulation depth of 100% can be easily attained at a lower input power. The experimental results are in good agreement with the theoretical predictions. Approximately 26 dB of RF signal gain in the band from 1 to 18 GHz is achieved in the experiment with this technique. Finally, the transmission experiment shows that this technique can effectively improve the performance of radio-over-fiber systems.

A symbol detection scheme based on the Viterbi algorithm that simultaneously processes subsets of 2-D data in the presence of Gaussian noise was recently proposed for binary 2-D optical storage (TwoDOS). In the case of multilevel TwoDOS, a straightforward full-fledged maximum likelihood symbol detector, or even the previous Viterbi-based algorithm, is not an ideal solution due to complexity restrictions. We propose a suboptimum low complexity symbol detector, which still performs within the accepted performance bound for optical storage. We describe the procedures involved in designing and developing a practical symbol detection scheme for multilevel TwoDOS by analyzing the signal values generated by a linear channel model in the presence of Gaussian noise. Our proposed detection scheme exploits the properties of the 2-D data format on the disk, and is flexible enough to accommodate performance and complexity restrictions for optical storage applications.

In short-distance optical links, the development of driving circuits for vertical-cavity surface-emitting lasers (VCSELs) requires precise and computationally efficient VCSEL models. A small-signal model of a VCSEL is computationally efficient and simple to implement; however, it does not take into account the nonlinear output behavior of the VCSEL. In contrast, VCSEL models that are highly based on first principles cannot be implemented in standard circuit device simulators, because the simulation of eye diagrams becomes too time consuming. We present another approach using VCSEL models, which are based on the 1-D rate equations. Our analysis shows that they combine efficient extraction and short simulation time with an accurate calculation of eye diagrams over a wide range of ambient temperatures. As different implementations of the rate equations exist, tradeoffs between three different versions are presented and compared with measured GaAs oxide-confined VCSELs. The first model has a linear and the second a logarithmic function of the gain versus the carrier density. The third model considers the additional transport time for carriers to reach the active region with quantum wells. For parameter extraction, a minimum set of parameters is identified, which can be determined from fundamental measurements.

CMOS technology downscaling is expected to encounter a metallic interconnect bottleneck in the near future due to increasing delays of global on-chip interconnects, signal distortion, and timing uncertainty (skew and jitter), as well as power consumption. Silicon-compatible integration of optical on-chip interconnects is presented as an alternative solution. Integrated optics using silicon-on-insulator single-mode waveguides, Si-based modulators, and Ge photodetectors offers a feasible way to distribute the global clock over the whole chip. Taking into account the photodetectors' characteristics, with a CMOS-inverter-based transimpedance front-end amplifier and additional gain stages to ensure sufficient voltage swing, the performance of optical global clock distributions is compared with that of their metallic counterparts. The main advantages brought by optics include signal propagation with negligible distortion over centimeter-long distances (pulse spreading <1% of the clock period at a frequency of 100 GHz), reduction of skew and jitter in comparison with electrical repeater lines (optical skew/jitter <3% to 4% at a frequency of 50 GHz), lower sensitivity to temperature variations (optical delay variation <1.8% for a 100-K variation), and reduction of the total chip power consumption (negligible power consumption for the global clock distribution: <70 mW).

We describe a technique for distance measurement in applications that require moderate precision. The technique is based on interference fringes resulting from the differing optical path lengths of two Gaussian beams traveling through the arms of a Michelson interferometer. From a propagation analysis of the beams, we find an expression that relates the distance between two surfaces and the resulting phase map from intensity images, making unnecessary the continuous tracking of the order of interference. The range of measurement of the method can be varied by the proper selection of the focal length of an expanding lens, from a fraction of a millimeter to a few centimeters.

Based on current trends in research on techniques for repairing composite materials, this paper focuses on the compatibility between a light-cured repair material and composite materials. The repair material used in this study is intended to find applicability in techniques for repairing damaged composite materials. Test pieces of the composite material were excited by a sinusoidal acoustic source at a frequency of 1058 Hz. Time-average holographic interferograms were photographed in original, damaged, and repaired samples. By analyzing the three interferograms according to the principles of holographic interferometry, the utility of the light-cured repair material is shown.

We present a design for a switchable phase shifter that can be incorporated in a Michelson interferometer. This arrangement uses a pair of ferroelectric liquid-crystal devices with nominal retardations of a quarter wave and a switching angle of 45 deg. It produces phase shifts of 0 and ±90 deg that are almost independent of the wavelength over the range of visible wavelengths.

Numerical procedures for construction of digital patterns of fringes mimicking fluid holograms are developed. Because conventional finite-element fluid analysis techniques are based on the approximation of nodal displacements, conjugate smoothing of the values of volumetric strain is performed in order to obtain realistic holographic images. Two-dimensional fluid oscillations are analyzed using the developed techniques. It is shown that though time-average fluid holography is a powerful optical experimental method for analysis of short-term transient processes and harmonic vibrations, it has rather limited applicability to studying propagating waves.

The performance of mobile laser communication systems operating within Earth's atmosphere is generally limited by the pointing errors due to movement of the platforms and mechanical vibrations. In addition, atmospheric turbulence causes changes of the refractive index along the propagation path, creating random redistribution of the optical energy in the spatial domain. Under adverse conditions these effects lead to increased bit error rate. While traditional approaches provide separate treatment of these problems, suggesting high-bandwidth beam steering systems for tracking and wavefront control for the mitigation of atmospheric effects, the two tasks can be integrated. This paper presents a hybrid laser beam-steering–wavefront-control system comprising an electrically addressed spatial light modulator (SLM) installed on the Omni-Wrist sensor mount. The function of the Omni-Wrist is to provide coarse steering over a wide range of pointing angles, while that of the SLM is twofold: wavefront correction and fine steering. The control law for the Omni-Wrist is synthesized using a decentralized approach that provides independent access to the azimuth and declination channels; calculation of the required phase profile for the SLM is optimization-based. This paper presents the control algorithms, the approach to coordinating the operation of the two systems, and the results.

Recent papers comparing weak-scintillation data from wave-optics simulations with predictions derived from the Rytov perturbation method for ground-to-space Gaussian beams have revealed a region of inaccuracy in the Rytov-based predictions. The discrepancy region is defined by beam diameter and focus settings that place the target in the beam far field and the turbulence in the transmitter near field. Under such conditions turbulence-induced beam wander dominates the scintillation at the target. We develop a solution to the turbulent propagation physics that is applicable in the discrepancy region, and demonstrate agreement in scintillation behavior with our own wave-optics simulation data and with predictions from a rigorous extended Huygens-Fresnel analysis. A combination of our solution and Rytov-based scintillation theory can be used to yield accurate scintillation predictions throughout the weak-scintillation regime for ground-to-space beams. Separately, we show that Rytov-based scintillation theory best describes the physics of a wander-tracking transmitter (where beam wander has been removed from the propagation physics) at the mean transmitter aim point on the target plane, as opposed to the physics of a stationary transmitter.

Recently, an extension of the Navy Aerosol Model (NAM) was proposed based on analysis of an extensive series of measurements at the Irish Atlantic Coast and at the French Mediterranean Coast. We confirm the relevance of that work for the distant eastern Meditteranean and extend several coefficients of that coastal model, proposed by Piazzola et al. for the Meditteranean Coast (a form of the Navy Aerosol Model), to midland Middle East coastal environments. This analysis is based on data collected at three different Middle East coastal areas: the Negev Desert (Eilat) Red Sea Coast, the Sea of Galilee (Tiberias) Coast, and the Mediterranean (Haifa) Coast. Aerosol size distributions are compared with those obtained through measurements carried out over the Atlantic, Pacific, and Indian Ocean Coasts, and Mediterranean, and Baltic Seas Coasts. An analysis of these different results allows better understanding of the similarities and differences between different coastal lake, sea, and open ocean zones. It is shown that in the coastal regions in Israel, compared to open ocean and other sea zones, larger differences in aerosol particle concentration are observed. The aerosol particle concentrations and their dependences on wind speed for these coastal zones are analyzed and discussed. We propose to classify the aerosol distribution models to either: 1. a coastal model with marine aerosol domination; 2. a coastal model with continental aerosol domination (referred to as midland coast in this work); or 3. a coastal model with balanced marine and continental conditions.

Differential absorption radiometry (DAR), using uncooled detectors, is a simple, low-cost method for passive remote sensing of hazardous chemicals for domestic security applications. However, radiometric temperature differences (ΔT_effective) between a target gas species and its background affect detection sensitivity. Two DARs with sensitivities to methanol, diisopropyl methylphosphonate (DIMP), and dimethyl methylphosphonate (DMMP), all spectral or physical simulants of hazardous chemicals, were developed and used to experimentally determine the effect of |ΔT_effective| on detection sensitivity. An analytical model was also developed and compared with the experimental results. With a signal-to-noise ratio (SNR)<5, a |ΔT_effective|≥2 K is sufficient for rapid (≤1 s) detection of methanol at <0.03 atm cm and DMMP and DIMP at <0.001 atm cm. These measured sensitivities suggest that rapid detection of hazardous chemical vapor clouds below lethal dose concentrations can be achieved using room-temperature pyroelectric detectors. Measurements were within 3% of the analytical predictions.

The multiple-classifiers approach is utilized to fully take into account the complementary and supplementary information from different data sources for terrain cover classification. To combine the outputs of classifiers that may be conditionally dependent, a variance reduction technique was adopted for optimal voting and thus best information extraction. The effectiveness and efficiency of utilizing the variance-reduction technique was demonstrated using SAR and optical images. Results show that the classification accuracy is dramatically improved by the proposed method.

Infrared surveillance systems have the task of detecting small moving targets having low signal-to-clutter ratio. Detection is usually accomplished by (1) removing the background structures from each frame and (2) integrating the target signal over consecutive frames of the residual sequence. We focus on the analysis of background removal techniques based on linear and nonlinear two-dimensional filters such as the window average, median, max-median, and max-mean. We introduce two modified versions of the window average and max-mean filters, where an appropriate guard window is used to reduce the bias due to the target. We define an ad hoc methodology to compare the different background estimation techniques on the basis of their ability to suppress background structures and to preserve the target of interest. Finally, we present and discuss the results obtained over two experimental IR sequences containing a highly structured background.

A bundle of aluminum hollow-core fibers is used to deliver ArF-excimer-laser light. The hollow cores are purged by a simple gas injection system to prevent the generation of ozone gas. For a 1-m-long bundle that is composed of 40 fibers each with an inner diameter of 0.7 mm, the straight loss is about 1.2 dB. The bundle also offers advantages of easy beam coupling and a high damage threshold.

This paper describes the implementation of a part of the JPEG 2000 algorithm (MQ decoder and arithmetic decoder) on a field-programmable gate array (FPGA) board by using dynamic reconfiguration. A comparison between static and dynamic reconfiguration is presented, and new analysis criteria (spatiotemporal efficiency, logic cost, and performance time) have been defined. The MQ decoder and arithmetic decoder are attractive for dynamic reconfiguration implementation in applications without parallel processing. This implementation is done on an architecture designed to study the dynamic reconfiguration of FPGAs: the ARDOISE architecture. The obtained implementation, based on four partial configurations of the arithmetic decoder, allows one to reduce the number of logic cells significantly (by 57%) in comparison with static implementation.

We present a novel fractal encoding method, based on a full-binary-tree searchless iterated function system (FBSIFS), that encodes image range blocks based on a fixed-location domain block. This algorithm is capable of encoding much smaller range blocks than traditional fractal algorithms, extending to 2×2 and 2×1 range blocks or even single image pixels. The FBSIFS method employs a rectangular block decomposition, similar in nature to the more general horizontal-vertical partitioning scheme. However, the proposed method has a simpler structure, similar to quadtree partitioning. Experimental results show that this algorithm is capable of providing superior performance, in terms of encoding time, compression rate, and reconstructed image quality, to traditional search-based fractal methods. The searchless binary-tree partition method also has better performance than searchless quadtree partition methods. A comparison with existing search-based and searchless fractal algorithms is presented, including compression rate, peak SNR of the reconstructed image, and algorithm complexity. A JPEG comparison is also presented.

A class of partition-based interpolators that addresses a variety of image interpolation applications are proposed. The proposed interpolators first partition an image into a finite set of partitions that capture local image structures. Missing high resolution pixels are then obtained through linear operations on neighboring pixels that exploit the captured image structure. By exploiting the local image structure, the proposed algorithm produces excellent performance on both edge and uniform regions. The presented results demonstrate that partition-based interpolation yields results superior to traditional and advanced algorithms in the applications of color filter array (CFA) demosaicking and super-resolution reconstruction.

Foveated imaging systems applicable in various single-user displays mimic the visual system's image structure, where resolution decreases gradually away from the fovea. The main benefit is the low average image resolution while maintaining high resolution at the center of the gaze. When the end user is a human observer, it is advantageous for the foveation process to closely match the visual system parameters. This work directly applies a multichannel model of the visual system to form foveated images. A systems-engineering approach applied to the vision model produces quantitative image spectral content across the visual channels. Foveated images are constructed according to the contrast threshold and image content calculated at different eccentricities. Also, variable-resolution feature detection (edge and bar) that corresponds to early visual processing is produced, based on the available image content across the channels. Motion between shifted foveated images (required in applications such as image compression and motion compensation) is estimated using either the foveated images or the detected feature images. Results using several similarity metrics and imaging conditions show that reliable motion estimation can be achieved, while features with nonsimilar resolutions (different scales) are matched.

The reconstruction of spectral reflectances of objects being imaged is important in reproducing a color under a variety of viewing illuminants. In this work, a simple formula is derived to evaluate the quality of a set of color image sensors aimed at reconstruction of spectral reflectances, and it is applied to multispectral image acquisition systems. Since the quality depends not only on the spectral sensitivities but also on the noise present in the systems, it is impossible to evaluate a set of sensors without prior knowledge of the noise present in it. Therefore, the noise variance of the multispectral cameras is estimated by a new proposal, and it is applied to the evaluation for the first time. It is shown that the experimental results agree well with the predictions by the evaluation model, and that the method to estimate the noise variance is useful for the evaluation.

A method of data fusion from a set of range images for 3-D object surface reconstruction is presented. The two major steps (multiview registration and data integration) of data fusion are carefully discussed. Firstly, the range images taken from multiple views are accurately registered through a set of translation and rotation matrices whose coefficients are carefully calculated through the developed methodology. Then, three criteria for overlapping-data elimination are provided as the foundation of data integration. Compared with the most other methods, which mesh all multiple views or compute an implicit surface function for the object before integrating the data, our integration method manipulates surface data directly, thus providing a straightforward way for overlap removal. A surface-based smoothing filter and a resampling operation are also developed for data quality improvement and data size reduction. The approach is applied to various range data sets of objects with different geometric shapes. The experimental results demonstrate the efficiency and applicability of the proposed method.

We assess the performance of a novel three-dimensional double directional filtering (3DDDF) algorithm for detecting and tracking weak moving dim targets against a complex cluttered background in infrared (IR) image sequences. This proposed method increases the target energy accumulation ability further than the three-dimensional directional filter (3DDF) method. Prior to the filtering, a new prewhitening method termed a three-dimensional spatialtemporal adaptive prediction filter (TDSTAPF) is used to suppress the cluttered background. Extensive experiment results demonstrate the proposed algorithms' ability to detect weak dim point targets against a complex cloud-cluttered background in real IR image sequence and the performance comparisons of the proposed method and 3DDF.

A novel dense stereo matching algorithm based on propagation within a Voronoi decomposition of the image plane is proposed. A weighted sum of squared differences is developed as the cost function. The size of the window is adaptive; it is set in inverse proportion to the texture density inside it for reliable propagation. A simple way to detect possible areas of depth discontinuities is developed to determine the search regions. A significant merit of the algorithm is that it can be applied to a wide variety of images, including those with large disparities, with or without rectification. It has been verified on real images, with satisfactory results.

A backup resource reoptimization scheme is presented. The presented scheme dynamically adjusts backup lightpaths and reoptimizes the optical network resources. Link load and link reliability that vary with time are considered in this reoptimization scheme. Reserved backup lightpaths are dynamically adjusted to avoid traversing both the heavily loaded links and the unreliable links during the network operation. A heuristic algorithm is presented to achieve fast online backup resource reoptimization. Simulation results show that the presented backup resource reoptimization scheme reduces the network blocking probability while improving the robustness of optical networks against multiple link failures, and thus improves the network performance.

We describe a time-integrating acousto-optic correlator (TIAOC) developed for imaging and target detection using a wideband random-noise radar system. This novel polarization interferometric in-line TIAOC uses an intensity-modulated laser diode for the random noise reference and a polarization-switching, self-collimating acoustic shear-mode gallium phosphide (GaP) acousto-optic device for traveling-wave modulation of the radar returns. The time-integrated correlation output is detected on a 1-D charge-coupled device (CCD) detector array and calibrated and demodulated in real time to produce the complex radar range profile. The complex radar reflectivity is measured in more than 150 radar range bins in parallel on the 3000 pixels of the CCD, improving target acquisition speeds and sensitivities by 150 over previous serial analog correlator approaches. The polarization interferometric detection of the correlation using the undiffracted light as the reference allows us to use the full acousto-optic device (AOD) bandwidth as the system bandwidth. Also, the experimental result shows the fully complex random-noise signal correlation and coherent demodulation without an explicit carrier, demonstrating that optically processed random-noise radars do not need a stable local oscillator.

Stabilized and tunable optical output are very necessary for fiber ring lasers applied to wavelength-division multiplexing (WDM) for communications and optical sensor systems. In general, a fiber Fabry-Perot (FFP) filter can provide wavelength tuning inside the ring cavity of the fiber ring laser. Because of the bandwidth limitation of erbium-doped fiber amplifiers (EDFAs), the operation region of erbium-doped fiber (EDF) ring lasers extends only from C to L band (1530 to 1610 nm)1- 2 and thus must be supplemented with the proposed S-band fiber ring laser.3 Actually, the wideband ring laser must use a long length of EDF even to approach C- plus L-band operation.1 However, that is insufficient to stabilize the lasing wavelength and power of a fiber ring laser. Recently, several remedial techniques, such as integrating two cascaded FFP filters of widely different free spectral ranges (FSRs) into a cavity,4- 5 using a compound ring resonator composed of a dual-coupler fiber ring and a tunable band pass filter,2 adding an extra ITU-grid periodic filter in the optical loop,6 and employing an integral saturable-absorber-based tracking narrowband filter,7 have been reported experimentally.