This PDF file contains the editorial “An Exciting New Addition to Your Journal” for OE Vol. 39 Issue 08

We present an improved computation of crosstalk between single-mode rectangular optical waveguides for application to planar lightguide circuit design, and apply our analysis to several doped silica waveguide examples of practical importance. The results are compared with previous calculations of crosstalk as well as with the results obtained from a simulation (beam propagation) program.

The quantum efficiency and the crosstalk of a photodiode in a long wavelength IR (LWIR) 2-D diode array are studied by numerically solving the 2-D diffusion equation of photocarriers in an array environment. The quantum efficiency depends strongly on both the diode size and the junction depth, and can be expressed, to good accuracy, as a quadratic function of the two variables. The results, corresponding to HgCdTe n+-on-p backside illuminated photovoltaic (PV) diodes, are compared with published Monte Carlo results and with analytical (1-D) special cases. For a given pitch, smaller diodes have lower crosstalk, but also lower quantum efficiency. This implies an optimal diode size. The highest quantum efficiency is obtained for low junction depths (? 1 ?m), and the optimum diode size, maximizing the quantum efficiency and minimizing the crosstalk, lies in the range of 15 to 30 ?m for a pitch of 50 ?m over a wide range of diffusion lengths. The quantum efficiency depends weakly on the pitch, for a given ratio of diode size to the pitch.

An optical double random-phase encryption method using a joint transform correlator architecture is proposed. In this method, the joint power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Unlike the case with classical double random-phase encryption, the same key code is used to both encrypt and decrypt the data, and the conjugate key is not required. Computer simulations and optical experimental results using a photorefractive- crystal-based processor are presented.

A new video segmentation algorithm using a combined segmentation measure for content-based coding is presented. The combined segmentation measure is a weighted sum of intensity, motion, and a change segmentation measure. The change segmentation measure is defined from a change image, which is obtained from the proposed change detector. The proposed change detector performs morphological erosion filtering to eliminate many inaccurate components, included in the resulting image obtained from a conventional change detector. Since the change segmentation measure is defined as an absolute change value difference between a pixel and its neighboring region, it can be an efficient segmentation measure for the accurate segmentation of neighboring moving objects and static background regions. Therefore, the proposed combined segmentation measure can determine exact boundaries even though the estimated motion vectors around the boundaries of moving objects and static background regions are inaccurate and the intensities around the boundaries are similar. From the experimental results for a video segmentation, since the combined segmentation measure can accurately segment the boundaries between moving objects and static background regions, the motion compensated images produced by the proposed segmentation algorithm show improved image quality compared to the conventional segmentation.

We propose a new class of finite-state vector quantizers (FSVQs), called gradient match vector quantizers (GMVQs), in the image coding framework. GMVQs can be considered more general than previously proposed side match vector quantizers (SMVQs) since more border pixels between two neighboring blocks are considered in the state codebook design. Moreover, the concept of gradient matching used in GMVQs can be adjoined to another previously proposed overlap match vector quantizers (OMVQs). Thus another new class of FSVQs are proposed and named as gradient and overlap match vector quantizers (GOMVQs). GMVQs and GOMVQs utilize the 2-D spatial continuity of the pixel gradient as well as the high spatial correlation of pixels in typical grayscale images. Both minimize the gradient errors of the border pixels between blocks in ordinary vector quantization of images. In addition to reducing the granular noise that causes the annoying effect of visible pixel block boundaries, the proposed GMVQs and GOMVQs also can preserve the global gradient among the block boundaries and reduces more step noise than SMVQs and OMVQs in the area of high contrast edges. Experiments with the ‘‘Lena’’ image show that the proposed GMVQ can achieve the performance superior to those of SMVQ maximum more than 1 dB peak signal-to-noise ratio (PSNR) under the same bit rate. On the other hand, GOMVQs can achieve further bit rate reduction (about 0.14 to 0.3 bit/pixel) than OMVQ using the variable length noiseless code for the channel symbols.

We propose an efficient fractal video coding algorithm that exploits the correlation between range cubes. Four domain cubes mapped by the previous neighboring range cubes are considered as the good candidates for the input range cube. Two search methods, which take advantage of the correlation between intercubes in the spatial and spatial-temporal directions, are developed to reduce the computational complexity in the encoding phase. In order to raise the compression efficiency, a search-order coding technique is applied to encode the candidate domain cubes. Simulation results show that when the proposed method is implemented with a fast fractal video coding algorithm, it can further reduce the encoding times and bit rate with insignificant loss of video quality.

The problem of reconstructing signals from their noisy and randomly shifted observations is considered. Our approach is different from existing methods in the choice of slices in the bispectrum domain. Up to now only a single 45 deg slice or multiple parallel-to-axis slices have been used to recover signals. These algorithms either are prone to low signal-to-noise ratio (SNR) estimates or improve SNR of high frequency estimates only. We propose an algorithm that accumulates multiple bispectral radial slices and use the accumulation to recover both the Fourier phase and the magnitude of the signal. Major advantages of the new algorithm are the reduced estimation errors and improvement in SNR in the whole frequency band. A mathematical formulation of the algorithm is given and fast algorithms are presented along with other implementation issues. Performance is evaluated using both simulated data and real radar data. Experimental results show that the proposed algorithm compares favorably with existing methods in terms of mean squared reconstruction error and computational complexity.

We introduce a contrast-based image fusion method using the wavelet multiresolution analysis. This method includes three steps. First, the multiresolution architectures of the two original input images are obtained using the discrete wavelet transform. A new concept called directive contrast is presented. Second, the multiresolution architecture (MRA) of the fused image can be achieved by selecting the corresponding subband signals of each input image based on the directive contrast. Finally, the fused image is reconstructed using the inverse wavelet transform. This algorithm is relevant to visual sensitivity and is tested by merging visual and IR images. The result shows that the fused image can integrate the details of each original image. The visual aesthetics and the computed SNRs of the fused images show that the new approaches can provide better fusion results than some previous multiresolution fusion methods.

A recently developed method for the restoration of motion- blurred images is investigated and implemented for the special complicated case of image blur due to sinusoidal vibrations. Sinusoidal vibrations are analyzed in the context of blur identification and image restoration. The extent of the blur and the optical transfer function (OTF) are identified from the blurred image by a straightforward process without the use of iterative techniques. The blurred image is restored using a simple Wiener filter with the identified OTF. The main novel achievement is the use of only a single vibrated blurred image as input information, on which the restoration process is based. The various cases of blur types that depend on the imaging conditions are considered. Examples of blur identification and image restoration are presented.

single-template algorithms are useful when the orientation of the target is known. However, if a target's exact aspect angle is unknown a priori, then multiple templates may be combined to yield a distortion- tolerant filter. In addition, the presence of environmental degradation between the target and the observer degrades the detection and classification performance of electro-optical sensors. We introduce a minimum- mean-squared-error filtering algorithm that takes into account the environmental degradation, additive system noise, nonoverlapping background noise, and target distortions. This distortion-tolerant filter is shown to be tolerant of different target aspects, and detects true class targets well in complex scenes.

An efficient algorithm is proposed for the interpolation of interlaced images. On the basis of the edge-based line average (ELA) algorithm, tow useful measurements are introduced within the operation window in order to alleviate misleading decisions in determining the direction where the interpolation is to be made. By efficiently estimating the directional spatial correlations of neighboring pixels, increased interpolation accuracy has been achieved. In addition, the new method is simply structured and is therefore easy to implement. Extensive simulations conducted for different images and video sequences have shown the efficacy of the proposed interpolator, with significant improvement over previous ELA-based algorithms.

We report a technique for the measurement of transient outof- plane displacement gradients in plane objects by double-pulsed subtraction TV shearography. The fringe patterns are automatically and quantitatively analyzed by the Fourier transform method. A novel optical setup based on the separation and further recombination of illumination beams is demonstrated for the generation of carrier fringes. The principle of the proposed technique is theoretically described, and its immunity to environmental disturbances is discussed. Experimental results obtained with a metallic plate excited by the impact of a piezoelectric transducer are presented.

In modern manufacturing, the main workpiece error results from spindle thermal deformation. We introduce a method to measure spindle thermal deformation using three single-beam interferometers. Ours is a noncontact, real-time measurement method that can be carried out while the spindle is rotating. An experiment is performed on a vertical machine center, and a measurement uncertainty of 1.0 ?m is obtained for a spindle thermal deformation of 50 ?m.

Two-stages are planned to measure the 3-D profile of objects by using the phaseshifting method, based on shadow moire topography. The stages essentially consist of moving the grating vertically, which produces a change in the moire pattern, and rotating the grating, which results in a constant phase shift regardless of the moire fringe order. In practice, an additional stage of moving the grating horizontally has to be added, which averages the grating period and yields a better moire pattern. We aim to improve the shortcomings inherent in the conventional method, such as complicated operation of the optical arrangement, and our emphasis is on describing the novel methodology and justifying it by an error simulation test. The experimental results show that this technique is available for practical applications.

The influence of the in-plane displacement and doubleaperture orientation on the slope fringe formation in double-shearing- aperture speckle interferometry is discussed in detail. The research results show that the two in-plane displacement components, one parallel to and the other perpendicular to the shearing direction, have an influence on the slope fringe formation and that the double-aperture orientation also has an important influence on the slope fringe formation. A theoretical analysis and experimental results are presented. The experimental results are in good agreement with the theoretical analysis.

The behavior of nematic liquid crystals in spatially varying electrical fields is investigated. Director profiles of nematic-liquid-crystal phase gratings are simulated for different orientations of the liquid-crystal director field with respect to the electrode grating. With increasing spatial frequency of the grating the fringing electric field becomes important and the diffraction pattern changes. The optical properties are analyzed and measurements are performed.

Surface relief gratings on eosin dye soaked gelatin films are created on exposure to polarized cw diode pumped Nd:YAG laser beam at 532 nm without any subsequent processing steps and the progression of the grating inscription is monitored by measuring the growth of the intensity of first order diffracted beam over time with 633 nm beam of a He-Ne laser. Diffraction efficiency of the grating is found to depend on time of exposure, intensities and intensity ratio of the interfering beams, and concentration of the dye in gelatin. A diffraction efficiency up to 30% is observed. The recording is predominantly surface relief. The surface modulations of the grating generated are investigated using an atomic force microscope.

The simplest two qualitative geometrical tools to evaluate lenses and mirrors are the Ronchi and Hartmann tests. They only require a knife or a ruling and a point light source. Frequently, the main desired characteristic of a test is not high sensitivity and precision, but speed and simplicity. The test proposed in this paper does not require any additional lenses, other optical elements, or even point light sources, making it quite simple. Its sensitivity greatly depends on the actual testing configuration. In the test to be described here only a flat screen with an array of straight and parallel lines is necessary.

A method is proposed for measuring the focal length of microlenses based on the propagation properties of a Gaussian beam. The beam waist is measured before and after the beam passes through the microlens. Experimental results were obtained by measuring a microlens formed by the drawing method. The results obtained are compared with those from other methods and differ by less than 10%.

Multichannel pattern recognition based on the projection of the components of a multichannel image onto a vector followed by single-channel matched filtering is presented. The projection preprocessing reduces the multichannel information to a single channel, while most of the necessary information is maintained. We describe the design of an optimal filter in terms of robustness to additive noise. A phase-only filter obtained on the basis of the optimal filter can be used for optical pattern recognition. One advantage of the phase-only filter described here is its improved robustness to noise. Computer simulation results are provided to illustrate multichannel pattern recognition using the proposed method.

The geometrical aberrations theory of a centered system is applied to calculate the third order aberrations of the optical system based on two spherical mirrors (the so-called Schwarzschild objective). The role of each of the third order field aberrations in the formation of the view field is analyzed. The scaling effect (i.e., the relationship between the optics' geometrical dimensions and the spatial resolution) is studied. The performance of a 21 x Schwarzschild objective (including the nonconcentric scheme) is investigated using a ray-tracing computer simulation. The tolerances of the axial and lateral alignments of the Schwarzs- child objective are found and the results are used to design a soft x-ray optical system based on multilayer mirrors to provide low geometrical aberrations (spatial resolution about 0.05 ?m) and a view field up to 300 ?m. Soft x-ray imaging microscope experiments demonstrate good accordance with the predicted performance of the optics. High resolution optics such as these can be a good basis for the optical instrumentation in soft x-ray microscopy, extreme ultraviolet lithography (EUVL), microanalysis, etc.

We present a finite-element method to calculate 3-D surface profiles of refractive microlenses fabricated by melting-resist technology (reflow technique). The geometry of the microlenses can be arbitrary. Surface tension and gravity are taken into account. Gravity can have an advantageous influence on the profile form, so that smaller focal spots can be achieved. A simple scaling law is given to estimate the influence of gravity on the profile form for given microlens parameters. We compared various theoretical and measured surface profiles of microlenses fabricated by melting-resist technology and found good agreement. Finally, the usefulness of this method for the design of refractive microstructures for smart masks is shown.

We report the development and demonstration of a fiber optic accelerometer. The principle of operation is based in the use of chirped Bragg gratings where the chirp width varies as the grating is physically deformed. The theory of operation is presented and experimentally compared with a conventional accelerometer's measurements for a vibrating beam.

A temperature fiber sensor based on CdSe-nanocrystallite- doped phosphate glass as a sensing element is reported. This glass is shown to exhibit a reversible temperature-induced absorption edge shift at temperatures less than the annealing temperature of the glass (<370°C). A dual-wavelength detection scheme based on a reflective grating and bi-cell photodiode is employed to eliminate the effects of variable signal losses in the intensity-dependent sensor. A sensor prototype, tested in the temperature range of -20 to +120°C, is shown to exhibit a linear response to temperature variations.

We report an in-line digital holographic sensor (DHs) for monitoring and characterizing marine particulates. This system images individual particles over a deep depth of field (>25 cm) with a resolution of 5 ?m. The DHS projects a collimated beam through the water column and onto a lensless CCD array. Some light is diffracted by particulates and forms an object beam; the undeflected remainder constitutes the reference beam. The two beams combine at the CCD array and create an in-line hologram, which is then numerically reconstructed. The DHS eliminates many problems traditionally associated with holography. The CCD recording material considerably lowers the exposure time and eliminates most vibration problems. The laser power needs are low; the DHS uses a small 10-mW diode laser. Rapid numerical reconstruction eliminates photographic processing and optical reconstruction. We successfully operated the DHS underwater on a remotely operated vehicle; our test results include tracing a single particle from one hologram to the next, thus deriving a velocity vector for marine mass transport. We outline our digital holographic reconstruction procedure, and present our graphical user interface and user software tools. The DHS is particularly useful for providing in situ ground-truth measurements for environmental remote sensing.

An optical method of detecting a liquid level is presented that uses fluorescence radiation generated in an impurity-doped glass or plastic slab. In operation, the slab is inserted into the liquid and pump light is coupled into it so that the light is guided by the slab-air interface above the liquid and escapes into the liquid just below its surface. Since the fluorescence is generated only in that section of the slab above the liquid, the fluorescence power will monotonically decrease with increasing liquid level. Thus, a relationship can be established between any signal proportional to it and the liquid level. Because optical fibers link the pump source and the detector of fluorescence radiation to the sensor, no electrical connections are needed in or near the liquid. Their absence vastly decreases the hazard associated with placing a liquidlevel sensor in a potentially explosive environment. A laboratory prototype, consisting of a methyl styrene slab doped with an organic dye, has been built and successfully tested in water. Its response to liquid level when pumped by a tunable argon-ion laser at 476, 488, and 496 nm, and by a blue LED, is presented and shown to be consistent with theory. The fluorescence spectra, optical efficiency, temperature, and other effects are also presented and discussed.

In a time-division-multiplexing (TDM) fiber optic sensor system, a continuous-wave laser source can be externally modulated by an intensity modulator to generate an optical pulse. To enhance sensor system performance, an optical pulse with a high extinction ratio (ER) is highly desirable. The high ER increases sensor sensitivity and reduces sensor crosstalk. For optimum TDM operation, it is important not only to select an intensity modulator with a high ER, but to operate the modulator at its most optimum operating point. We provide a way to achieve these goals. We demonstrate a control to maintain the output optical pulse from an optical guided-wave (OGW) intensity modulator at its maximum ER bias point. Our unique control methodology uses a reference value obtained after the process of amplifying, digitizing and averaging the input signal of the optical pulse. Results are analyzed and processed, using a custom software program and algorithm of our own design, and used to control the OGW, electronics maintaining the optimum bias point for best ER. Our experimental results show that this control scheme can be used to satisfactorily operate an OGW at high sensitivity with output optical pulse light intensity variation of less than 15 nW, which provides for improved TDM fiber optic sensor system response and operation.

The dynamic range of a Shack-Hartmann sensor is normally limited by the fact that the foci can leave their subapertures and so a definite attachment of the foci to their subapertures is difficult. One method for solving this problem is to give the focal spots a kind of label to identify them even if they leave their subaperture. We describe how the dynamic range of a Shack-Hartmann sensor can be expanded by using lenses with well-defined astigmatism. We also derive a relation between the spot displacements and the partial derivatives of the wavefront for large wavefront slopes.

The potential of different fiber Bragg grating pairs for simultaneous sensing of strain and temperature is analyzed. We demonstrate that interferometric interrogation of a fiber grating written in bow-tie fiber enables strain and temperature to be simultaneously determined. This is achieved by independent measurement of the shift in the wavelengths of the reflected light from the grating components along the fast and the slow axes of the hi-bi fiber. A detailed theoretical analysis is presented that includes the basic sensing principle, sensor design and demodulation scheme. The performance of the proposed technique in simultaneous measurement of temperature and strain is experimentally demonstrated and resolutions of ± 2.5° c/?Hz and ± 26 ??/?Hz are obtained for a fiber with birefringence of B = 5.5x 10-4.

The feasibility of sensing carbon dioxide with a IR singlebeam optical structure is studied, and a novel carbon dioxide gas sensor based on IR absorption is achieved. Applying the Lambert-Beer law and some key techniques such as current stabilization for IR source, using a high-quality IR detector, and data compensation for the influences of ambience temperature and atmosphere total pressure, the sensor can measure carbon dioxide with high precision and efficiency. The mathematical models for providing temperature and pressure compensation for the sensor are established. Moreover the solutions to the models are proposed. Both the models and the solutions to the models are verified via experiments. The sensor possesses the advantages of small volume, lightweight, low power consumption, and high reliability. Therefore it can be used in many associated fields, such as environmental protection, processing control, chemical analysis, medical diagnosis, and space environmental and control systems.

An optical fiber pressure sensor has been developed using a biconically tapered single-mode optical fiber. The sensor has a pressure range of 1265 mbar and a sensitivity of 0.008 dB/mbar. The main attributes of the presented intensity sensor are its ease of fabrication, good repeatability, and very low cost. That makes it very suitable for applications such as atmospheric pressure detection inside buildings, where it is being currently applied. It is also shown how to get higher-sensitivity sensors, following a similar fabrication procedure, for other possible applications.

A realization of laser-induced breakdown spectroscopy for real-time, in situ and remote analysis of trace amounts in liquid samples is described, which is potentially applicable to the analysis of pollutants in water in harsh or difficult-to-reach environments. Most of the measurements were conducted using a fiber assembly that is capable of both delivering the laser light and collecting the light emitted from the micro plasma, up to about 30 m from the target area. Alternatively, a telescopic arrangement for line-of-sight measurements was employed, with a range of 3 to 5 m. For internal standardization and the generation of concentration calibration curves, reference lines of selected elements were used. In the majority of cases calibration against the matrix element hydrogen was employed using the H?, H?, and H? lines, but also spiking with selected reference species was utilized. In order to provide high reliability and repeatability in the analyses, we also measured plasma parameters such as electron density, plasma temperature, and line- shape functions, and determined their influence on the measurement results. Numerous elements, including a range of toxic heavy metals, have been measured over a wide range of concentrations (Al, Cr, Cu, Pb, Tc, U, and others). Limits of detection usually were in the range of a few parts per million; for several elements even lower concentrations could be measured.

This paper describes theoretical analysis, fabrication techniques, and measurement results for frequency-selective surfaces operating in the millimeter and submillimeter wave region. The analysis is based on the method of moments with entire domain basis functions, obtained by the boundary-integral - resonant-mode-expansion method. This method is particularly efficient and applies to the analysis of thick metal screens perforated periodically with arbitrarily shaped apertures. Three fabrication techniques are discussed and applied: photolithographic etching, galvanizing growth, and milling. Prototypes obtained with the different fabrication techniques are presented. Finally, measurements of the frequency response of the prototypes are presented, based on a new spectroscopic tool called terahertz time-domain spectroscopy. In all cases, the measurement data fit very well with the simulations.

We approach the problem of point target detection in infrared image sequences by modeling the temporal behavior of clutter and targets on a single-pixel basis. These models, which are experimentally verified, are then used to develop a temporal likelihood-ratio test and derive the corresponding decision rule. We demonstrate the effectiveness of the technique by applying it to real infrared image sequences containing targets of opportunity and evolving cloud clutter. The physical models and resulting hypothesis-testing approach could also be applicable to other image-sequence-processing scenarios, using acquisition systems besides infrared imaging, such as the detection of small moving objects or structures in a biomedical or biological imaging scenario, or the detection of satellites, meteors, or other celestial bodies in night-sky imagery acquired using a telescope.

An experiment is described in which an automatic target recognizer (ATR) algorithm is tested against real forward-looking infrared imagery and synthetic imagery. The synthetic imagery was generated by two different approaches being developed by the U.S. Army. The purpose of the experiment was to establish quantitatively the relationship between ATR performance on real and on synthetic data. The metrics for comparison are probability of detection, conditional probability of identification, and false-alarm rate.

A statistical texture image metric, which is based on the Markov cooccurrence matrix and named ICOM, is introduced and evaluated in the context of the correlation between (1) human quantitative detection performance of targets and false alarms and (2) qualitative image judgments of both natural and enhanced infrared images. Correlations between the ICOM metric and experimental detection results are compared with those obtained with the probability of edge (POE) global clutter metric, the local contrast metric (DOYLE), and the combined signal-to-clutter (SCR) metric. In contrast with those metrics, which fit well either the qualitative or the quantitative results, the ICOM textural metric was found in good agreement with both the qualitative and quantitative experiments. Moreover, the ICOM metric was found appropriate for automatic extraction of potential false targets in both natural and the enhanced images. This property is used to analyze human false-detection-decision behavior, and to suggest a modification to the known constant false- alarm rate (CFAR) model. The modified model considers the total number of detection decisions (true and false) made by the human observer as the adaptive parameter. The model was tested and confirmed both with natural and enhanced images. The ICOM properties and the results obtained using them emphasize the robustness and the adequacy of this metric for infrared imagery evaluation.

A numerical model was developed to find the temperature distributions during radiant heating of a silicon wafer with SiO2 thin film patterns. The radiative properties of silicon and the film structure were found by considering the effects of partial transparency and thin film interference. The average total properties over simple patterns with feature sizes of the order of a few micrometers were found, using an average of the properties of each region within the pattern, weighted by their relative areas. In general, wafers with a single SiO2 film or pattern reach a higher steady state temperature than a plain Si wafer due to higher total absorptivity. This applies to thin films of any thickness below several micrometers, where coherent effects are dominant. The temperature of patterned wafers vary nonlinearly with film thickness, with the highest temperature discrepancy from Si wafer occurring at film thickness of ~0.2 ?m. For wafers with complex patterns, the temperature distributions can be estimated by the average of temperatures for simpler patterns, weighted by their respective areas. Due to limitations in the computational domain, the radiative processing of 3-in. wafers was modeled; however, results were confirmed for the 12-in. wafer for limited cases.