This PDF file contains the editorial “Editorial: We Are Indeed International” for OE Vol. 33 Issue 06

This PDF file contains the editorial “Guest Editorial: Optical Pattern Recognition” for OE Vol. 33 Issue 06

We propose an idea for security verification of credit cards, passports, and other forms of identification so that they cannot easily be reproduced. A new scheme of complex phase/amplitude patterns that cannot be seen and cannot be copied by an intensity-sensitive detector such as a CCD camera is used. The basic idea is to permanently and irretrievably bond a phase mask to a primary identification amplitude pattern such as a fingerprint, a picture of a face, or a signature. Computer simulation results and tests of the proposed system are provided to verify that both the phase mask and the primary pattern are separately readable and identifiable in an optical processor or correlator.

We consider the detection of candidate objects (regions of interest) in a scene containing high clutter, multiple objects in different classes, independent of aspect view, with hot, cold, bimodal, and partial object variations and with high and low contrast targets. We use three different filters with each designed to produce high probability of detection (P_D). We fuse the results from different outputs to reduce the probability of false alarms (P_FA). All filters are realizable on an optical correlator.

Correlation filters with three transmittance levels ( +1 , 0, and -1) are of interest in optical pattern recognition because they can be implemented on available spatial light modulators and because the zero level allows us to include a region of support (ROS). The ROS can provide additional control over the filter's noise tolerance and peak sharpness. A new algorithm based on optimizing a compromise average performance measure (CAPM) is proposed for designing three-level composite filters. The performance of this algorithm is compared to other three-level composite filter designs using a common image database and using figures of merit such as the Fisher ratio, error rate, and light efficiency. It is shown that the CAPM algorithm yields better results.

Several methods have been suggested for eliminating the undesirable convolutional and high-order-response terms in a binary phase-only filter (BPOF) (e.g., Zhang, Su, and Guo in 1987 and Davis, Cottrell, Davis, and Lilly in 1989). We show how our previously published (in 1992) analysis of the basic BPOF can be applied to these methods.

The problem of designing ternary phase and amplitude filters (TPAF5) that reduce the probability of image misclassification for a two-class image set is studied. The Fisher ratio is used as a measure of the correct classification rate, and an attempt is made to maximize this quantity in the filter designs. Given the nonanalytical nature of the design problem, a simulated annealing optimization technique is employed. Computer simulation results are presented for several cases including single in-class and out-of-class image sets and multiple image sets corresponding to the design of synthetic discriminant function filters. Significant improvements are found in expected rates of correct classification in comparison to binary phase-only filters and other TPAF designs. Approaches to accelerate the filter design process are also discussed.

The correlation performance of minimum noise and correlation energy (MINACE) synthetic discriminant function (SDF) filters and distortion-invariant ternary phase-amplitude filters (TPAFs) on visible-wavelength images of an actual tank on a natural terrain background is compared in simulations. The comparison is performed for four test images with three types of preprocessing: none, edge enhancement, and binarization. Testing is realistic in that it uses only scenes not included in the training images used to construct the filters. The implications of the results for correlator design are discussed.

The correlation performance of the binary joint transform correlator for multiobject detection is studied mathematically and experimentally using three types of thresholding methods. These thresholding methods include the spatial frequency dependent threshold function, the median thresholding, and the subset median thresholding. We provide a new expression for the image separation requirement in the input plane of the linear joint transform correlator for multiobject detection. Also, we introduce a new analytical approach for obtaining the threshold function in the binary joint transform correlator. The median thresholding method for multiobject detection by the binary joint transform correlator (JTC) is also analyzed. A hybrid optoelectronic setup is used for experiments. Two different implementations of the threshold function are employed in the experimental system. Experimental results of the binary JTC using different thresholding methods are determined and compared in terms of correlation peak-to-noise ratio, peak-to-sidelobe ratio, and space-bandwidth product. The results indicate that the binary JTC performs well for multiobject detection. Furthermore, using the threshold function in the binary JTC eliminates the first-order correlations between different input targets and the even-order harmonic terms in the output plane.

The images introduced to an optical pattern recognition system are normally an amplitude representation of the original intensity images. We define a method of encoding intensity images as phase-only images, and we demonstrate that the performance of the correlation is generally substantially better than that of the correlation performed with amplitude inputs. Energy in the correlation peak is about a factor of 20 greater for the phase-encoded input image method. These performance and energy advantages are particularly useful when designing filters that incorporate various degrees and types of invariance. We give examples and numerical results for the correlation process with ternary and 15-phase-state plus zero-amplitude filters with varying spans of invariance. We suggest practical implementations for this technique.

A major limitation on the optical joint transform correlator (JTC) is that the output plane is dominated by unwanted autocorrelation products. A new technique is proposed that uses time modulation and demodulation to separate the correlation components. Time modulation is applied to the JIG inputs, resulting in a time-modulated joint power spectrum. Demodulation of the transform plane separates the self-correlation components from the other terms. When the demodulated signal is the input to the second transform stage in the JTC the result is system peak-to-noise ratio/peak-to-secondary ratio (PNR/PSR) improvement, removal of input plane location constraints, and elimination of detection problems resulting from multiple targets. Two implementations are discussed. Using a general model for sinusoidal modulation, it is shown that amplitude, phase, and polarization modulation of the inputs all result in amplitude modulation of the correlation signals in the transform plane. The general solution is difficult to implement, because it requires temporal demodulation of the joint Fourier signal on a pixel-by-pixel basis. A more practical system results from the case of square-wave modulation, where it is shown that demodulation can be easily implemented through image subtraction using only two to four frames of data. This Fourier plane processing technique has been implemented using a binary JTC (BJTC). Performance improvement of 6 dB over the conventional BJTC is demonstrated through computer simulation and laboratory results.

The performance of optimal trade-off synthetic discriminant filters is illustrated in a particular application that consists of determining the angle and position of an airplane. A real-time numerical experimental system was realized using different airplane scale models. The performance of the system in response to different kinds of input perturbations is shown. The system allows us to obtain a 0.1-deg mean precision in the absence of noise. The mean precision is still better than 1 deg with an input SNR of about -22 dB. These results are obtained for 128- x 128-pixel input images. The system performance clearly demonstrates the effectiveness of the correlation technique for pattern recognition.

Synthetic estimation filters (SEFs) have been found useful for the determination of distortion parameters such as angle of rotation of objects from their images. Previous SEFs, designed using matched and phase-only filters required a knowledge of the exact location of the object to produce reasonable estimation accuracy. To overcome the limitation, use of minimum average correlation energy (MACE) filters is proposed for the construction of SEFs. Because the MACE filters are designed to have their peaks at the origin of the correlation plane, the peak can be detected without a knowledge of the exact position of the object. Computer simulations are used to study the performance of MACE-SEFs. It is found that significant errors result at rotation angles that are not part of the training set. An improved linearity leading to an increase in accuracy was realized when the minimum noise correlation energy (MINACE) concept was used in place of the MACE concept for the design of the SEFs.

We determined the performance of an optical correlator that used input images of N x N pixels to examine larger images of LN x LN pixels. The larger images were examined in parallel using a pyramid technique. We used morphological processing to approximate a low-pass filter to generate an image pyramid for a binary correlator. In correlation experiments we found that the discrimination between objects and SNR dropped with increasing L. Although the discrimination may remain useful, the more rapidly decreasing SNR limited the value of L that could be used. In addition, we showed by simulation the processing of a 512 x 512 pixel image from an infrared sensor with a 128 x 128 pixel binary optical correlator.

An efficient algorithm is proposed that recognizes a mixed document consisting of printed Korean/alphanumeric text and graphic images. In the preprocessing step, an input document is skew-normalized, if necessary, by rotating it by an angle detected with the Hough transform. Then we separate the graphic image parts from the text parts by considering chain codes of connected components. We further separate each character using vertical and horizontal projections. In the recognition step, a mixed text consisting of two different sets of characters, e.g. , Korean and alphanumeric characters is recognized. Korean and alphanumeric characters are classified and each is recognized hierarchically using several effective features. The output is obtained by combining the recognized characters and separated graphic parts. An efficient automated analysis algorithm for mixed documents consisting of graphic images and two different sets of characters is proposed and its performance is demonstrated via computer simulation.

We present the theoretical investigation of a novel architecture of a LiNbO₃ guided-wave optical processor suitable for real-time microwave imaging in on-board synthetic aperture radar (SAR) applications, using a moving platform on either an aircraft or a spacecraft. The new configuration, which is basically interferometnic, includes four Mach-Zehnder (MZ) modulators, each characterized by an additional aperiodic phase-reversal traveling wave modulator. The electrode configuration is appropriately designed to reproduce the product of the base-band SAR received echoes and two reference signals and, then, to perform both the range and azimuth compression. The two product signals are separately time integrated by two fast photodetectors. The sampled signals coming out of the detectors include both the required product signals and intermodulation products and are electronically filtered for reproducing the correct product with no amplitude distortion. At this stage, the signals are multiplexed and registered on a two-dimensional buffer to reproduce the final correlation functions for the range and azimuth directions. Because of the serial multiplication between the received echoes and reference signals, the circuit can operate with very long data streams. Our proposed processor can reproduce the images coming from ground features using a conventional chirp pulse SAR system with the antenna beam looking at 90 deg from the direction of platform motion. The circuit can operate at a free-space wavelength of 1.3 μm with a radiofrequency (rf) of 410 MHz, a response time/bandwidth ratio of ≈ 10^-5 μs/MHz, a linear dynamic range of ≈50 dB, and an SNR ≈8 dB, assuming chirp pulses as reference signals. The circuit performance is evaluated by considering lithium niobate as the substrate material and two different waveguide fabrication techniques: titanium indiffusion (Ti:L1NbO₃) and proton exchange with annealing (APE:LiNbO₃). The best results in terms of linear dynamic range and optical losses are obtained by the titanium indiffused channel waveguides. We calculated in any fabrication condition a swath range resolution of dσ ≈ 10 m in airborne simulation and about 60 m in the satellite simulation, whereas the azimuth resolution is about dρ = 1.5 and 6 m, respectively. Significant improvements in terms of SNR (90%) and SAR resolution (50%) are obtained by using binary pseudorandom sequences as reference signals, i.e., ≈15 dB, Δσ = 2 and < 58 m, Δρ ≈ 1.5 and 6 m, respectively.

This PDF file contains the editorial “Guest Editorial: Optical Science and Engineering in India” for OE Vol. 33 Issue 06

Fiber optic evanescent wave absorption sensors based on four different designs are described. The launching condition and the geometry of the sensing region are found to be the main parameters that can influence the sensitivity of the sensor. High sensitivity is achieved by launching the selected rays into the fiber having tapered sensing regions. The experimental results obtained are qualitatively explained using a simple model based on meridional rays.

We describe the construction and operation of an optical-fiber-based position-sensitive detector and a few of its applications. The p01-shed tip of a multimode fiber serves as an aperture with finite width and an avalanche photodiode coupled to the other end of the fiber functions as the optical detector. We demonstrate the utility of this detector system for imaging and mirage effect studies. Measurements made on a bulk sample of potassium nitrate (KNO₃) undergoing phase transition and surface imaging of a patterned brass disk are given as illustrations.

The optical techniques of stress analysis, such as, holography, photoelasticity, and moiré, produce results in the form of whole-field fringe patterns representing physical measurements. The accuracy of results will depend on how precisely fringe orders and fringe locations are determined. A detailed account of an accurate and automatic method of tracing the centerlines of dark and bright fringes using image processing is presented. The variance of gray-level values across fringe width is used as a criterion for determining fringe direction. The determination of fringe direction is done in an operator window of size 5 x 5, 7 x 7, or 9 x 9 pixels at the central pixel of the window. Sequential application of this condition enables the user to trace the fringe centerline. Using the capabilities of image-processing equipment, the cursor, and the specially developed computer program, holographic fringes of different patterns were traced. A few of these cases are presented as illustrative examples. It is also shown that the technique can be successfully applied to fringes that close on themselves so as to form closed loops.

An overview of the applications of holographic interferometry for spacecraft structural components at ISRO Satellite Centre, Bangalore, India, is presented. The details of the development of a dual vacuum stressing technique and its application for holographic nondestructive testing (HNDT) of honeycomb panels are presented. Results of some calibration studies conducted for HNDT of propellant tanks are also presented. It is found that holographic interferometry is quite useful, particularly for HNDT of honeycomb panels and propellant tanks used for spacecraft structural components.

A method for measuring the thickness of free-standing films of Formvar in the range of 2000 Å to 5 μm is presented. The optical path difference of the film with reference to air is measured using a modified Jamin interferometer, and the refractive index is determined by a thin wedge technique. The method provides thickness measurements with an accuracy of ±300 Å. The results are found to be in good agreement with those obtained from a profilometer. This simple method can be very useful for thickness measurement of free-standing thin plastic films for extreme ultraviolet (XUV) soft x-ray research applications.

A UV preionized TEA CO₂ laser suitable for high-repetition-rate operation is developed that utilizes inductive ballasted sparks for UV radiation to produce preionization and a saturable inductor for delay between preionizer and main discharge. Optimization study of laser performance with respect to various parameters is presented.

Performance characteristics of a transverse-gas-flow cw CO₂ laser in which dc discharge was sustained by simultaneous application of high-repetition-rate, high-voltage, short-duration electrical pulses are presented. This excitation scheme enabled maintaining a stable and uniform discharge with electrical input power density more than 15 W/cm³ in a typical laser gas mixture of 2 mbar CO₂, 14 mbar N₂, and 30 mbar He. Maximum laser power of 5.2 kW was obtained with 15% electro-optic efficiency from a pair of active regions each of 1-rn length incorporated with a folded stable optical resonator. The effect of water vapor on laser performance is also discussed.

The design and development of an efficient high average power dye laser oscillator-amplifier system developed at the Laser & Plasma Technology Division, Bhabha Atomic Research Centre, is reported. The dye laser is pumped by a 6.5-kHz repetition rate copper vapor laser. The signal beam to the dye amplifier is obtained from an efficient narrow-band grazing incidence grating (GIG) dye laser oscillator incorporating a multiple prism beam expander. Amplifier extraction efficiency up to 40% was obtained in a single amplifier stage, using rhodamine 6G (Rh6G) in ethanol. We have also demonstrated simultaneous amplification of two laser beams at different wavelengths in the same dye amplifier cell.

Operation of a discharge-pumped KrF laser consisting of an all stainless steel chamber and using pure argon as the buffer gas at subatmospheric pressure is reported. The optimized pulse energy of ~50 mJ was achieved from about 60 cm³ active volume and at ~36 kV charging voltage. The optimized pressure of the gas mixture was about800 mbar.

The diffraction theory of resonator modes fails to predict the output characteristics from short-inversion-time self-terminating lasers, because of insufficient time available for mode establishment. A geometrical approach based on repeated imaging of an initial spontaneous emission source in successive round trips by resonator optics is used to predict the output characteristics of such lasers. The effective size and the location of the image of the initial source, as seen from the output plane, determines the output divergence. Because of the widely different focal lengths of the two mirrors used in an unstable resonator, an asymmetry in the characteristics of the outputs from the two ends is expected. These predictions were tested in copper vapor lasers with a variety of stable, unstable, self-filtering unstable (SFUR), and diffraction-filtered (DFR) resonators. Output divergence close to the diffraction limit is obtained with SFURs and DFRs. The outputs from opposite ends of an unstable resonator show a difference in divergence of as large as a factor of three. It is shown that the proposed approach successfully explains the output characteristics.

The reflectance characteristics of biological tissues depend on their color, composition, and blood content. To determine these characteristics, a computer-based He-Ne laser light reflectometer, consisting of the microprocessor-controlled movement of the sample platform to scan the entire tissue and simultaneous transfer of data to a PC-AT to obtain the perspective plots, is developed. The results obtained from various tissues and their combinations show that the reflectance pattern, as obtained by this method, helps to identify the tissues as well as the abnormalities embedded with in these structures.

A 50-mm, f/1.4, six-element lens based on a new configuration has been developed for a 16-mm cinematographic projector. In this design, Indian-made Central Glass and Ceramic Research Institute (CGCRI) glasses are used. To compare the performance of this system, a separated six-element Petzval configuration based on U.S. Patent No. 2,541,484, Ex. 1, is designed under similar conditions of optimization using CGCRI glasses. The performance of both designs is compared using transverse aberration curves, energy distribution curves, and geometrical modulation transfer function (MTF) curves. These criteria for image evaluation indicate that the proposed new configuration gives better performance than the 16-mm motion picture projection lens based on the Petzval configuration. The same conclusion is also drawn from a comparison of resolving power at different field angles for both the systems.

An automatic, accurate mask alignment method, based on a modified moiré technique suitable for x-ray lithography is presented. In this technique, the alignment marks are in the form of gratings. The high slope region of the moiré signal is used to obtain higher sensitivity and better position control accuracy. Automatic alignment is achieved by using the difference of the moiré signal and its inverted signal obtained by computer. This difference signal is zero at a point in the higher slope region that is considered the correct alignment point. This difference signal is treated as an error signal, which is used for obtaining control signal by performing the proportional, integration and differential (PID) algorithm. The 12-bit analog-to-digital (A/D) and digital-to-analog (D/A) convertors are used to interface the piezoelectric-transducer- (PZT)-driven alignment system with the computer. Under the present experimental conditions, accuracy for alignment is of the order of ± 0.06 μm.

We present a theoretical evaluation of third-order susceptibilities appropriate for the Kerr effect of some doped alkali halides using an electronic anharmonic oscillator and three-dimensional coupled anharmonic oscillator models. We estimate the electronic and ionic contributions to the susceptibility and highlight the effect of doping on the nonlinearities of wide-bandgap crystals.

Submillimeter-wave generation through optical difference frequency mixing technique in lithium niobate (LiNbO₃) is discussed. Theoretical aspects as applicable in this connection are briefly considered. The possibility of utilizing frequencies within the spectral spread of solid state laser output for mixing purposes is reported.

We present the general solution of Maxwell's equations for TE modes in a dielectric medium characterized by an intensity dependent dielectric constant of the form ε = ε₁ α|E|² + γ|E|⁴. The solution is obtained for a bounded fifth-order nonlinear dielectric medium (i.e., for a film) that has been shown to lead in the limiting forms to the known solutions for the unbounded case (i.e., the medium forming a cladding or a substrate) and the solutions for the Kerr case (both bounded and unbounded cases).

Optomechanical scanners have a revolving mirror and discrete detector elements for different spectral bands. The lower integration time in these systems affects the SNR, which can be improved either by increasing the collecting aperture or by using more sensitive detectors. An increase in the collecting aperture causes an enormous increase in the total weight of the scanner system. CCD image sensors have better sensitivity than the discrete detector elements. Linear CCD image sensors make it possible to avoid the use of revolving mirrors that are required in optomechanical scanners. CCD image sensors have a wide spectral response that makes them particularly suitable for multispectral imaging. The design of a multispectral sensor consisting of a single lens and a complex prism with dichroic and total internal reflecting surfaces is presented. It provides accurate band-to-band registration and rugged construction. The acquired image is displayed on a UV sensitive paper in real time.

Current high-technology precision engineering sensors with submicrometer and even nanometer resolutions have become a necessity. Among the various types of noncontact high-resolution sensors, noninterferometric electro-optical (EO) sensors have their built-in preferential features. Earlier, we developed a triangulation principle based noncontact EO sensor with 0.01-μm resolution. By optimizing the design parameters of this EO sensor, the resolution has been enhanced by almost an order of magnitude. A piezoelectric transducer (PZT) mirror with 3 μm/kV excitation voltage has been used as the target surface. The details of experimental setup and the results arrived at are presented.

The bipolar point spread function (PSF) corresponding to the Wiener filter for correcting linear-motion-blurred pictures is implemented in a noncoherent optical processor. The following two approaches are taken for this implementation: (1) the PSF is modulated and biased so that the resulting function is non-negative and (2) the PSF is split into its positive and sign-reversed negative parts, and these two parts are dealt with separately. The phase problem associated with arriving at the pupil function from these modified PSFs is solved using both analytical and combined analytical-iterative techniques available in the literature. The designed pupil functions are experimentally implemented, and deblurring in a noncoherent processor is demonstrated. The postprocessing required (i.e., demodulation in the first approach to modulating the PSF and intensity subtraction in the second approach) are carried out either in a coherent processor or with the help of a PC-based vision system. The deblurred outputs are presented.

Bleaching of cresyl violet in polyvinyl alcohol due to irradiation by a laser beam at three chopping frequencies is investigated using the photoacoustic technique. The results indicate that the bleaching rate decreases with increase in chopping frequency. This can be used as a potential medium for holographic recording and information storage.

The Jaynes-Cummings model provides a useful means of studying several quantum electrodynamic effects in matter-radiation interaction. One such effect is the phenomenon of collapses and revivals of Rabi oscillations. Various aspects of this phenomenon are studied in terms of the dynamical evolution of the atom as well as the statistical properties of the field. In particular, the sensitivity of collapses and revivals on the initial photon statistics, the cavity field damping mechanism is highlighted. For this purpose the basic model of Jaynes and Cummings has been extended and modified. Some multiatom effects are also discussed.

An imaging system with its aperture fully open or with a multiaperture mask in front has been used for carrying out speckle shear interferometry. The shearing is achieved by installing shear elements in front of the imaging system. The multiaperture configuration has built-in in-plane displacement sensitivity, and hence shear fringes obtained from multiaperture shear interferometer always carry the in-plane displacement contribution. This problem does not arise when the full aperture of the lens is used. A three-aperture speckle shear interferometric technique is introduced here to separate the in-plane displacement and slope contributions from the shear interferogram. Detailed theoretical and experimental results are presented.

Capabilities of laser speckle photography, speckle shearing interferometry, and Talbot interferometry with circular gratings to measure the temperature profile of axisymmetric gaseous flames are studied. Detailed experimental and theoretical investigations are presented. The temperatures measured by these three techniques are compared with the temperatures measured by a platinum-platinum-rhodium thermocouple with an accuracy of measurement ±0.2% of full scale ±4 digits. Good agreement between them is seen.

A two-beam coupled photorefractive novelty filter is presented for real-time measurement of displacement components. In the optical configuration, the BaTiO₃ crystal is oriented such that the spatial phase shift between the dynamic grating and the interference pattern is + π/2. Time evolution of fringe patterns is analyzed. The technique is applied to speckle photography for real-time measurements of displacement components. Experimental results are given.

The theoretical and experimental studies made on the phenomenon of spectral shift due to source correlation after the discovery made by Wolf in 1986 are outlined.

An optical link can provide an interface channel for a focal plane array that is immune to electro-magnetic interference (EMI) and can lower the heat load on the dewar. Our approach involves the use of fiber optics and an on-focal-plane optical modulator to provide an interface to the focal plane array (FPA). The FPA drives the modulator with an electrical signal. We evaluated specially fabricated AlGaAs/GaAs multiple-quantum-well (MQW) optical modulators, operating near 840 nm, for analog modulation, and we have used the results to calculate the performance of an optical interface link using experimentally determined device parameters. Link noise and dynamic range for an analog link were estimated from a separate experiment using pigtailed fiber components. The performance of the MQW modulator system is compared to alternative strategies. Significant improvement in performance in comparison to conventional electronic interfaces appears to be possible.

A restoration filter based on the constrained least-squares principle is proposed for the restoration of images distorted by random point spread function and additive measurement noise. The proposed filter modifies the conventional constrained least-squares filter by incorporating the second-order statistics, such as correlations, about the randomness of the point spread function. For space-invariant imaging systems, the proposed filter can be implemented in the discrete frequency domain and its computations can be carried out using the fast Fourier transform. Simulation results show that the proposed filter outperforms the conventional constrained least-squares filter, which neglects the correlations of the random point spread function.

A scophony infrared scene projector (IRSP) was developed by AURA Systems Inc. for use in evaluating thermal imaging guidance systems. The IRSP is a laser-scanned projector system incorporating scophony modulation with acousto-optical (AO) devices to produce multiband 96 x 96 image frames. A description of the system and preliminary test results with the Seeker Endo/Exo Demonstration Development (SEEDD) breadboard interceptor are addressed.

IR reflection quarter-wave retarders (QWR5) are described that maintain the collinearity of the transmitted and incident beams. One QWR uses a symmetric prism of Ge (refractive index n = 4) with an apex angle of 119 deg. Light incident parallel to the base of the prism is totally refracted, without change of polarization, at the side faces of the prism that are coated with an appropriate transparent bilayer. Total internal reflection at the prism base produces the desired 90-deg retardance. The second QWR uses a right-angle Ge prism with its base coated with a PbTe layer (n = 5.1) to introduce the required phase shift at a 55.18-deg angle of incidence. The entrance and exit faces are antireflection coated with a polarization-preserving bilayer. Both QWRs are reasonably insensitive to small (±8 deg) angle-of-incidence errors.

A visible light (675-nm) laser diode is used as a variable coherence length source to allow the rapid adjustment to equal optical pathlengths of a fiber interferometer. The diode's spectral width, measured for decreasing drive current, changes from less than 0.2 to 16 nm. The corresponding change in coherence length is from 2.3 mm to 28 μm, bridging a significant portion of the gap between a gas laser and a broadband source. The fiber interferometer's air paths are first adjusted with the laser at high drive current, then fine tuned as the current is reduced below threshold. An experimentally observed interferogram confirms the theoretical prediction for fringe visibility at a current near threshold.

We present methods for determining the phase shifts in multiphase fringe analysis from the fringe image data itself, thus eliminating the requirement for prior knowledge or accurate control of the phase shifts. We also discuss methods for calculating the folded (wrapped) and unfolded phases, and quote the accuracy of the fringe analysis method for an example in which the correct result is known.

A theoretical development is presented for understanding and designing bilateral symmetric optical systems. This development uses concepts familiar to the optical engineer and is an extension to the wave theory of axially symmetric systems. An aberration function is developed and the image position and size, image defects, and aberration fields are discussed. The main dependence of aberrations as a function of system parameters is established by a set of approximate aberration coefficients and some guidelines to approach the design of bilateral symmetric systems are presented.

Complex optical systems commonly employ adjustable optical mounts for alignment purposes. The design of a low-cost adjustable mirror mount that provides simple tilt and height adjustments is described. This mirror mount employs conventional machining and standard off-the-shelf hardware and is, therefore, very suitable for low-cost rapid prototyping applications. A diamond-machined metal mirror is directly assembled to the mount with three screws and two precision dowel pins. The adjustments are provided by three spring-loaded screws between the mount and a fixed base plate. Two set screws are used for locking purposes after the adjustments have been made.

Although amorphous silicon (a-Si:H) is very photosensitive and can be doped n and p type, it does not give effective phototransistors because of the extremely poor diffusion lengths. Hence enhanced photodetection in two-terminal a-Si:H devices is of considerable interest. Using the Analysis of Microelectronic and Photonic Structures (AMPS) computer model, we explore enhanced photodetection possibilities in two-terminal a-Si:H structures and show situations where it can occur. These situations, which we then experimentally verify, are of two types: one can yield quantum efficiencies greater than unity and the other can yield gains of 10³. Both of these enhanced photodetection situations occur because of what we term photogating.

A vision system that acquires spatial coordinates (range data) of three-dimensional objects by triangulation using structured light is presented. The developed system requires only a single image and guarantees unambiguous correspondence by using a uniquely encoded light pattern. Using a single image enables the system to perform in a dynamic environment, which contains moving objects. An example is presented.

This PDF contains the communications for "Extension of Freeouf's model of Schottky barrier height to composite systems."

This PDF contains the communication for "Orientation and position detection of surface-mounted devices and printed circuit boards using the high-precision fuzzy Hough transform."

This PDF file contains the editorial “Book Rvw: Optical Fiber Amplifiers: Design and System Applications," by Anders Bjarklev for OE Vol. 33 Issue 06

This PDF file contains the editorial “Book Rvw: Testing and Evaluation of Infrared Imaging Systems," by Gerald C. Holst for OE Vol. 33 Issue 06