This PDF file contains the editorial “The Journey” for OE Vol. 41 Issue 01

We report the experimental demonstration of evanescent-wave gas detection with a silica-air microstructure fiber. Detection sensitivity of ~6% of that of direction absorption spectroscopy per equal length has been achieved. 0]

This PDF file contains the editorial “Advances in Pattern Recognition Techniques, Devices, and Algorithms” for OE Vol. 41 Issue 01

A new theory of the Fourier-transform property of a lens, based on geometrical optics instead of diffraction and wave optics, is presented. This simple theory is useful for quick understanding of optical correlators and other Fourier optical processors.

In a previous report, we developed optimization algorithms showing how optical correlation filters operating with obscured inputs were affected by disjoint constant background illumination. We extend these studies by upgrading our algorithms to include the theoretical treatment of zero-mean disjoint noise, as well as constant background illumination. Computer simulations involving noise clutter but no background illumination are used to characterize the performance of our upgraded algorithms.

A new hit-miss transform (HMT) algorithm is proposed to detect distorted multiple objects in clutter. The HMT in morphology is used to locate a specific object in an input image. But the standard algorithm of the morphological HMT may cause problems in detecting various true- class objects. To provide efficient recognition of various true-class objects in the input image, a new optical hit-miss morphological transform using the synthetic structuring element (SE) is proposed. The synthetic hit SE is composed of the intersection of all true-class hit SEs, and the synthetic miss SE is composed of the complement of the union of all true-class hit SEs. Simulation results show that the proposed algorithm can be used for the recognition of various true-class objects in an unknown input scene with only one HMT operation.

The design of a digital-optical hybrid correlator is detailed. The design of the optical-Fourier-transform lens and the mechanical lens housing are detailed, as well as the video-rate fast-Fourier-transform digital signal-processing hardware and overall electronic control. Example results using several different filters and modulation techniques are described.

The performance of two nonlinear joint transform correlators?the binary subtracted joint transform correlator and the photorefractive-based subtracted joint transform correlator, has been tested by computer simulations under brightness changes of various target scenes. The input images used in the study were composed of pure- amplitude, pure-phase, and complex data, respectively. Also the performance for input images with complex data transformed by a spatial light modulator that uses the electroabsorption effect of GaAs single crystal has been compared with the mentioned results. The input images with pure-phase and complex data gave better results than those with pure- amplitude data, for various input images with the brighter target scenes. However, the input images with pure-amplitude data were most robust to brightness changes of target scenes.

Two new wavelet transforms for noise-insensitive edge detection are analyzed and discussed. The proposed method is useful for lead inspection of surface mount devices in the electronic industry.

The method described represents an attractive compromise between the use of a single filter for a number of image distortions and one filter for each image or distortion of an image. The goal of this work is the generation of a number of filters, each of them being able to recognize a number of distortions. One of the main problems of the filter design is its high sensitivity to internal noise of the system, optical aberrations, etc. In this work, the most common case of image distortion invariance has been considered together with system noise invariance. The simulation results indicate the absence of a false alarm and good identification. The filter generation is based on a learning process in an electro-optical pattern recognition system. The genetic algorithm serves as an optimization method. A binary filter has been selected as the spatial filter. The comparison between a traditional matched spatial complex filter and this adaptive binary filter performance indicates the significant benefits of the latter. Statistical tools were used to estimate and compare the significance of the difference between the output average of a rejection and recognition image sets.

Target detection techniques play an important role in automatic target recognition (ATR) systems because overall ATR performance depends closely on detection results. We propose a multisensor target detection technique based on adaptive feature-based fusion suitable to detect low-contrast and/or blurry targets with relatively low computational complexity. The proposed technique extracts four different features designed to find regions of high contrast, strong edges, or high information content. The proposed multisensor target-detection technique incorporates multiple imaging sensors in different spectral ranges, such as the visible, near-infrared, and far-infrared bands. The images from the multiple sensors are jointly processed via feature extraction and multisensor fusion. In the multisensor fusion process, a multisensor confidence image is created by adaptively combining the features generated from the multisensor images to obtain more accurate potential target locations. Experimental results on multisensor test sequences are provided.

A novel approach is proposed to improve the discrimination of the radial-harmonic filter for shift- and scale-invariant pattern recognition. The approach combines the morphological correlation and the radial- harmonic expansion, in which the reference gray-level image is first decomposed into a series of binary images, and then the radial-harmonic expansion is applied to those binary images. The morphological radial- harmonic correlation is achieved by correlating the single-order radial- harmonic components with the corresponding sliced binary images obtained from the input scene and summing the correlations. The algorithm is tested via computer simulations. The results show that the algorithm is shift- and scale-invariant and provides better discrimination ability than the conventional radial-harmonic filter.

The projection-slice theorem has been used to create synthetic-discriminant-function based matched filters that are capable of discerning rotation and scale distortions. We propose to use the projection-slice algorithm for invariant face recognition that is capable of accommodating in-plane and out-of-plane 3-D distortions. The projection-slice algorithm is applied to training images in order to synthesize a composite image to represent each class. The optoelectronic fringe-adjusted joint transform correlator (JTC) technique is then used to correlate the test images with the composite images of each class. That technique was chosen for its superior performance to alternative JTCs and the feasibility of its implementation in the all-optical domain. Simulation results are furnished to prove the effectiveness of the proposed system.

Pattern recognition of small ship inverse synthetic aperture radar (ISAR) images is considered. This represents a formidable new distortion-invariant pattern recognition problem. New weighted correlation range alignment and weighted multiple-scatterer motion compensation variations to standard image formation steps were developed and used. A new algorithm to determine if an input image is useful was developed and found to be necessary for small ship ISAR data. Initial recognition results using distortion-invariant (composite) filters are presented. These provide new concepts including: use of a validation set and a goodness measure to select filter parameters, use of new output criteria for which a filter in a bank of filters is best for class determination, rejection of decisions on some poor test input images, and use of voting over a time sequence of test inputs.

We present results of a correlation filter utilizing a computergenerated hologram using an analog ferroelectric liquid-crystal spatial light modulator (SLM). The SLM amplitude-modulates light and can induce a 0-? phase shift, which is equivalent to modulating along the real axis. Two pixels are combined into a macropixel using a phase-detour technique enabling full complex modulation. The method is used as the filter for a conventional optical correlator and in a digital-optical hybrid correlator.

We demonstrate a new type of time-integrative photorefractive device using self-pumped phase conjugation. This device can be used for most of the applications related to time-integrative devices, such as demultiplexors and phase-sensitive detectors. A new device for angular multiplexing-to-frequency multiplexing conversion is proposed. By combining this new device with frequency demultiplexing, we show a new architecture for retrieving holograms from different holographic storages and for performing various arithmetic operations on the retrieved information.

We evaluate the target recognition performance of five optimal filter correlators for targets that are partially obscured by a disjoint background pattern of constant illumination. The optimal filters are based on cascading a matched filter with a correction filter to optimize a selected metric. In the two correlators with superior performance, the correction filter includes a term that correlates a phase extracted portion of the template with a phase extracted portion of the input signal. We also propose a restriction on these optimized correction filters, which preserves the conventional sense of template matching.

The optical fractional correlation is a very useful tool for partially controllable spatially varying correlation-based pattern recognition. It is shown to be a good match to fuzzy associative memory that performs partial fuzzy associations in parallel. We exploit the potential application of the spatially varying fractional correlation in implementing parallel fuzzy association. Computer simulations illustrate our conclusions.

A color pattern recognition system must identify a target by its shape and color distribution. In real situations, however, the color information is affected by changes of the light source (e.g., from indoor illumination to outdoor daylight), often making recognition impossible. In this work, we propose a color pattern recognition technique with tolerance for illumination changes within the common sources of white light. This can be accomplished using the coordinates of the CIELAB system, luminance (L*), chroma (C*), and hue (h*) instead of the conventional RGB system. The proposal has some additional advantages: there is no need to store a matched filters base to analyze scenes captured under different light sources (one set of filters for each illuminant light source) and therefore the recognition process can be simplified; and in most cases, the contribution of only two channels (C* and h*) is enough to avoid false alarms in color pattern recognition. From the results, we show that the recognition system is improved when CIELAB coordinates are used.

Optical information processing can perform a myriad of signal processing operations. It is primarily due to the complex amplitude processing capability. Optical information processors are capable of performing one- or two-dimensional operations using simple linear operators. However, it would not happen without the support of coherent property of illumination. We discuss the coherent optical complex transformation, by which information data processing can be exploited. A brief scan of Fourier and spatial domain processing, composite filtering, larger capacity photorefractive processing, optical neural computing, and others is shown.

We measured the characteristics of a quadrant-type avalanche photodiode (APD). Its transition region between the adjacent cells had a narrow width of 35 ?m. As the multiplication factor of the quadrant APD was limited by the variety of that among the quadrant cells, the maximum multiplication factor was about 30. We investigated the performance on applying the quadrant APD to a laser tracking system. A noise- equivalent angle of less than 1 ?rad (rms) was achieved at a received optical power of more than 4 pW. The quadrant APD compared favorably with a photodiode quadrant detector when the received power was less than 100 pW.

A key issue in the development and deployment of model- based automatic target recognition (ATR) systems is the generation of target models to populate the ATR database. Model generation is typically a formidable task, often requiring detailed descriptions of targets in the form of blueprints or CAD models. We propose a method for generating a 3-D target model directly from multiple SAR images of a target obtained at arbitrary viewing angles. This 3-D model is a parameterized description of the target in terms of its component reflector primitives. We pose the model generation problem as a parametric estimation problem based on information extracted from the SAR images. We accomplish this parametric estimation in the context of data association using the expectation-maximization (EM) method. Our model generation technique operates without supervision and adaptively selects the model order. Although we develop our method in the context of a specific data extraction technique and target parameterization scheme, our underlying framework is general enough to accommodate different choices. We present results demonstrating the utility of our method.

A new method of generating color in liquid crystal displays using birefringent filters is shown. This method has the benefit of high light transmission and color saturation compared to traditional spatial or temporal multiplexing methods, which include highly absorptive color filters. We discuss the design and optimization of a double-layer supertwisted nematic color display based on polarization interference filters. The viewing angle of such a device is also modeled and improvements are shown. The device is capable of high light transmission (90% that of parallel polarizers) while retaining color saturation.

We have investigated the utility of wavelet filters for enhancing contrast in the digital speckle pattern interferometric fringes obtained from a vibrating loudspeaker diaphragm and from the vibrating bracket of an electric motor. Experimental results reveal that use of properly chosen other filters along with the wavelet filter gives better enhancement. Our investigations also show that if the data are preprocessed by median filtering before implementing the wavelet filtering, then a weakly diffusing object requires a higher-kernel filter and strongly diffusing object requires lower-kernel one.

A state-of-the-art review of distributed optical fiber sensor technologies has been carried out. The studied methods include polarization-modulation-based, Brillouin-scattering-based, and frequency-modulated continuous-wave (FMCW) methods as well as optical coherence domain reflectometry (OCDR) and interferometric distributed sensing techniques. A classification of the methods with their main properties for measuring quantity information continuously from a long sensor fiber is carried out. The main emphasis is on the comparison of the methods with respect to their spatial resolution, measurement time, and measurement range. The FMCW methods are found to be the most versatile techniques for various applications, due to their short measurement times with measurement ranges extending up to tens of kilometers and location sensing resolution better than 0.1%. The OCDR methods are fast and compete with the FMCW methods in versaility, especially when the measurement range is shorter than 1 to 2 km.

A physics-based analytical model for an optically biased GaAs metal-semiconductor field effect transistor, suitable for simulating optoelectronic integrated circuits, is presented. The main objective of the model is to show the effect of optical radiation and temperature on important parameters such as the bandgap energy, mobility, and carrier lifetime. It is found that optical radiation has negligible effect on these parameters, but the temperature affects them significantly. The effect of different scattering mechanisms on the drain-source current is also studied. Using this analysis, the model extends to describe optical radiation and temperature-dependent device characteristics such as the threshold voltage, transconductance, cutoff frequency, transit time, and responsiv- ity. Under illumination, a significant enhancement in device transconductance leading to an increase in cutoff frequency is observed.

Several recent applications in ellipsometry, spectropolarim- etry, and multiplexed galvanometric scanners require a single compact beamsplitter capable of splitting an input beam of light into four or more components. Of special interest is the design of a single beam splitter to produce multiple components of equal power for incident unpolarized or circularly polarized light. We present a specific infrared design of a parallel-slab beamsplitter that uses a fused silica, which is strip-coated with a Ge thin film on the front and a uniform Ag coating on the back. Equal powers among the first four components can be achieved when the unpolarized reflectance levels on the first, second, third, and fourth strip are ?20, 68, 54, and 18%, respectively. Specific designs at wavelengths of 1.55, 2.02, and 5.0 ?m are presented. At a wavelength of 5.0 ?m, glass shows some absorption and is replaced by another transparent slab material. The choice of optical materials and thicknesses of the strips provide sufficient flexibility in the design and operation of the beamsplitter.

The calibration of a laser stripe profiler consisting of a laser stripe projector, camera, and linear motion table is considered. A nonlinear system model is used, which accommodates radial distortion in the camera lens. The way in which stripe data is extracted from the camera images leads to a natural formulation of the calibration problem as a nonlinear least squares problem. This can then be solved using standard techniques. The use of this nonlinear model reduces the error in the generated 3-D data by over an order of magnitude.

We report the first field experiment on the monitoring of black crusts by fluorescence lidar. Black crusts are an aesthetic and structural damage to the external parts of stone monuments mainly caused by atmospheric deposition. The experiment carried out on the cathedral (duomo) in Pisa, Italy, demonstrates that the presence of black crusts change the fluorescence spectra of the stone substrates in both shape and absolute values. All the investigated black crusts have the similar spectral signature and characteristic behavior.

Measurement error for NO2 profiling in the lower troposphere, including the effects of aerosol backscatter, molecular backscatter, and extinction due to inhomogeneous aerosol distribution, is estimated for vertical NO2 concentration profiles measured by differential absorption lidar (DIAL). Vertical NO2 concentration profiles of 0 to 40 ppb and null profiles are obtained for an altitude of 900 to 2250 m with a 150-m range resolution. The deviation of the null profiles from zero, which provides a measure of how precisely the laser beams were aligned, was <2.0 ppb. The mean statistical error, systematic error from aerosol, and absorption cross section error were 3.4, <3.0, and <1.2 ppb, respectively.

Optical diffraction has been demonstrated to be a useful method with which to noninvasively examine materials and structures that result from lithographic processes used in the semiconductor industry to create integrated circuits. The process of inferring the geometry of the lithographically created structures from measurements of diffracted power is rather difficult, due to the highly nonlinear relationship between the properties of the diffracting structure and the diffraction measurements. To simplify this process, we describe a method that is based on determining the departures from a set of expected design values. We show that this method linearizes the otherwise highly nonlinear relationship between structure parameter values and diffraction measurements, and hence permits analyses using classical linear methods. We develop a linearized inversion technique to determine key parameters of a periodic structure from an analysis of diffraction data, and illustrate the proposed method for the retrieval of three geometrical parameters (groove depth, linewidth, and sidewall slope angle), both individually and together. We tested our method using simulated measurements of power diffracted by the grating, which were generated using rigorous coupled- wave theory. We show that our inversion algorithm predicts the correct value of these three parameters for a variety of geometrical configurations.

Planar optical waveguide structures in communication network applications require a number of indispensable features, e.g., low insertion loss, efficient fiber-to-chip coupling, polarization independent operation, and high integration density, as well as reliable and cost- efficient fabrication. The presented concept of integrated optical waveguide structures is based on the high refractive index material system of silicon-oxynitride on silicon. This system has the potential to meet all mentioned requirements. We describe the design and fabrication of such waveguide structures and demonstrate basic integrated optical components with good performance.

A comprehensive theoretical model is developed to describe mid-IR laser radiation propagation in an optical cylindrical waveguide. The effects of various parameters of the beam as well as of the waveguide on the output beam shape are studied and analyzed. parameters such as beam coupling misalignment, waveguide diameters, and inner wall roughness are studied. The same conditions are applied in the theoretical calculations as well as in the experiments. Good agreement between the theoretical and experimental results is found.

We discuss an open photoacoustic cell study on sulfer-doped n-type InP wafer. The thermal diffusivity of the sample is evaluated from the phase data associated with the photoacoustic signal as a function of the modulation frequency under heat transmission configuration. Analysis is made on the basis of the Rosencwaig-Gersho theory and the results are compared with those from earlier reported photoacoustic studies of semiconductors. Our investigation clearly indicates that the instantaneous thermalization process is the major heat diffusion mechanism responsible for the photoacoustic signal generation in an InP sample.

We propose an eminent scene change detection (SCD) algorithm, and also present a new video-indexing method for fast content- based browsing and retrieval in video databases. The first step in our approach is to extract representative frames by using the proposed SCD algorithm from the Motion Picture Experts Group (MPEG) video sequence. Thereafter, we perform the video indexing by applying the rosette pattern (RP) to the extracted representative frames, and retrieve them. A principal cause of these processing procedures is that the performance of video indexing and retrieval system depends on the SCD. And how accurately SCD performs as well as a preprocessing are some of the considerations that we must take into account. Therefore, we classify every possible scene change that may happen within the video into three types: abrupt, gradual, and flashlight. And we detect every kind of scene change. Our SCD algorithm is better than the conventional ones in terms of SCD performance and we demonstrate its superiority by experiments. We also extract representative frames that represent series of detected scenes by the proposed accumulative histogram intersection measure (AHIM). Finally, we apply the RP to extracted representative frames for indexing, we can remarkably reduce the number of pixels (NOP) required to index and excellently retrieve the video scene.