This PDF file contains the editorial “Editorial: Territorial Distribution” for OE Vol. 30 Issue 10

Radial metrology combines standard optical measurement techniques with a unique panoramic annular lens (PAL) system to study material properties and deformations on the inner surfaces of the cavities found, for example, inside pipes, tubes, and boreholes. A PAL profilometer using speckle metrology is analyzed and the equations obtained from the analysis are used to calibrate the PAL profilometer when it is used to profile the inner surface of a cylindrical pipe and to measure the deformation of the pipe when it is subjected to diametral compression.

The feasibility of a system for the classification of machined surfaces based on the 2-D analysis of a diffraction pattern obtained by suitably illuminating the sample is discussed. Preliminary experimental results, obtained with a nonparametric Bayesian classifier, are presented.

The problem of range image segmentation is considered, and the relative performance of combinations of several differential geometric features such as the orientation and tilt angles of the normal, Gaussian curvature, and mean curvature is evaluated. A very fast and simple histogram-based segmentation scheme for polyhedral objects and reliable segmentation methods based on modified K-means and Unsupervised Fuzzy Partition-Optimum Number of Clusters (UFP-ONC) algorithms are presented. These methods are computationally and implementationally simple, work for both polyhedral and curved objects, are robust enough to deal with noisy features, and perform well without any knowledge of the type and number of objects present. Modifications to the K-means and UFP-ONC algorithms are necessary to deal with periodic features such as the orientation angle of the normal. The combination of orientation angle and mean curvature is shown to produce the best results, and the modified UFP-ONC algorithm is shown to perform better in terms of detecting more meaningful clusters, picking the optimum number of clusters and handling noisy data. Experimental results on range images obtained from the Environmental Research Institute of Michigan illustrate that the proposed methods are effective.

Image compression at rates oflO:1 orgreatercould make picture archiving and communication systems (PACS) much more responsive and economically attractive. A protocol is described for subjective and objective evaluation of the fidelity of compressed/decompressed images compared to originals. The results of its application to four representative and promising compression methods are presented. The four compression methods examined are predictive pruned tree-structured vector quantization, fractal compression, the full-frame discrete cosine transform with equal weighting of block bit allocation, and the full-frame discrete cosine transform with human visual system weighting of block bit allocation. A protocol was developed for side-by-side observer comparison of reconstructed images with originals. Three 1024 x 1024 computed radiography (CR) images andtwo 512 x 512 x-ray computed tomography(CT) images were viewed at six bit rates by nine radiologists at the University of Washington Medical Center. The radiologists' subjective evaluations of image fidelity were compared to calculations of mean square error for each decompressed image.

The generalized maximum likelihood (GML) algorithm is a gradient-based iterative algorithm for frame-to-frame motion estimation. This algorithm tends toward the maximum likelihood estimates of the Karhunen-Loève expansion coefficients of the motion field. The GML algorithm requires the covariance function matrix as a priori knowledge. Determination of the actual motion covariance in a practical situation is a difficult problem; the problem is approached by assuming that the motion vector is modeled by a separable stationary Markov-2 field. Using this model, we relate and compare the GML algorithm to another well-known motion estimator reported by Netravali and Robbins. Simulation experiments are presented that indicate the improvement of the GML algorithm over Netravali's scheme.

A simple and universal technique is presented for compressing digital still pictures consisting of both graphics and natural images, each very different in nature. It is based on a nonseparable, two-dimensional, adaptive resampling scheme combined with adaptive quantization of the color intensity values. We show that the new method we propose encodes edges with high accuracy while compressing uniform regions with minimal contouring effects. A generalization of the concept yielding a modified quadtree-based coding scheme perfectly suited for two-dimensional data compression is also included. Finally, compression criteria that allow minimization of both the encoding time and the hardware complexity in the encoder is discussed.

An optical processor for phased-array antenna beamforming has been demonstrated. It is capable of providing real-time control of both antenna beam steering and beam shaping in one or two dimensions, with an rms phase linearity of 5 bits. The functions of beam shaping and steering are combined through a magneto-optic spatial light modulator (SLM), which is fast, small, and simple to use.

A systematic procedure for calculating the general transfer function of a cascaded linear optical system working under the Fresnel regime is presented. The validity of neglecting the quadratic phase factors is also discussed. For the case of inhomogeneous optical devices with Gaussian profiles, explicit expressions for the transfer functions are calculated through specific Gaussian integrals.

An optical implementation is considered for a novel system, recently invented by the author, for accurately locating objects, relatively close to an array, from distributed backscatter. Processing is partitioned into handling scatterers in annuli rather than in pie-shaped regions as in conventional systems that use beamforming followed by matched filtering. The advantages of the new design are discussed. Precomputing a matrix containing geometric and transmission pulse information leaves only matrix-vector computations to be performed in real time. An optical processor is proposed because a large number of these computations must be performed in real time and because optics is well suited to matrix-vector computation. Experimental results are shown for 100 by 100 matrix-vector multiplication with a new device, a spatial light rebroadcaster (SLR). A method of constructing an optical sonar is proposed using the new concept and an optical matrix-vector multiplier. Much faster devices would be required for the method to be practical for a radar processor because of the much higher sampling rates.

A technique for segmenting focal planes to complement spinning frequency modulation (FM) reticles in tracking applications is presented. The technique involves the relaxation oftwo parameter constraints in the FM reticle equation. The advantages are a reduction in susceptibility to countermeasures and increased resolution. The disadvantages are increased electronics loading and a reduction in the maximum trackable target size.

The results of two electro-optical implementations of the alternating projection neural network (APNN) are presented. Both configurations use optical matrix-vector multipliers with electronic feedback, but different spatial light modulators are employed. The first implementation is passive, employing a photographic transparency that intensity-modulates the incident incoherent light. In the second implementation, two spatial light modulators actively modulate the light, permitting real-time updating of the interconnection matrix elements. To the authors' knowledge, the implementations described are the first of the APNN.

A grating pattern projected onto an object deforms in accordance with the three-dimensional shape of the surface. This deformed image can be analyzed by detecting the shifted phase of the original grating pattern with the aid of Fourier transformation. The profile of the object is expressed in moiré contours as well as in a wire-frame model for the intuitive understanding of the shape. In this procedure, multiplication and visibility enhancement of moiré fringes are performed with an improved result.

Mathematics are developed to transform a moiré pattern into a 3-D Fourier space. Grating shapes, tilt, heterodyning, phase shifting, and Fourier filtering are all easily visualized in the 3-D Fourier space. It is shown why, in general, a moiré pattern cannot be interpreted in the 2-D spatial domain by a simple algorithm operating on a point. A moiré pattern is defined in terms of the 3-D Fourier space. A simple algorithm is developed to generate the value of the moiré pattern at a point. The filter characteristics of a solid state camera are developed and exploited. Phase modulation and synchronous detection are shown to filter out only components due to the fundamental harmonic of the reference grating. The specimen frequency vector is recovered from the moiré phase field.

Charge-coupled devices (CCDs) of interline transfer design are especially useful in imaging at high frame rates. However, their sensitivity to ionization radiation and the reduced effective opacity of vertical charge transfer registers cause undesired image artifacts. Random white spots from the radiation and "ghost" images (or smear) generated in the registers may severely impair the image quality. An electronic method of eliminating these artifacts is described. Special sequences of pulses clock the CCD, quickly dumping the unwanted charge. The fast readout of images, cleared of artifacts, follows immediately. Results obtained with the Fairchild Weston CCD 222 imager are shown.

The clipping method is used to carry out the fast calculation of a correlation function of speckle intensity in several applications. Using this technique, the peak position of the cross-correlation function can be determined more accurately than that for the nonclipped one. There are several possible logical operations for calculating clipped speckle intensity. Several methods of the logical operation of the intensity clipping are studied to evaluate the accuracy of the peak detection of the clipped correlation function. Both the theoretical consideration and experimental results are given.

Laboratory-scale negative-branch unstable ring resonators were designed to simulate large Fresnel number, large-mode cross section positive-branch high-power ring lasers. These laboratory-scale lasers can be built having small-mode cross sections, long lengths, and large Fresnel numbers by incorporating imaging systems within the resonators. Large variations of Fresnel numbers can also be obtained by simple positioning of the output aperture. To verify that the diffractive modes of the high-power lasers are accu rately si mulated, ba re cavity mode discri mi nation properties of these ring resonator designs were calculated by various 3-D diffractive models. Modeling was completed for resonators with equivalent Fresnel numbers up to 1 1 and with equivalent Fresnel numbers of 10 and above using a fast Fourier transform (FFT) and a virtualsource code, respectively. Comparison of the FFT and the virtual source code results, at moderate Fresnel numbers, indicated good agreement between the different modeling techniques. Good mode discrimination was observed at half-integral equivalent Fresnel numbers, whereas poor mode discrimination was observed at integral equivalent Fresnel numbers. These results show that less computational intensive codes, such as the virtual source code, can quickly and cheaply model a resonator having a wide range of Fresnel numbers. These results also show that the equivalent Fresnel number of a near-imaging negative-branch ring resonator is a reasonably valid parameter for determining resonator diffractive phase and irradiance profiles even for resonators having large Fresnel numbers. The modeling results show that the modes of positive- and negative-branch resonators, having the same Fresnel number, behave the same to within a complex conjugate.

A methodology is presented for the characterization of atmospheric effects on the propagation of target contrast. The basic concept is to compare matched images simultaneously along a common line of sight from two imagers-one close up or in the near field and the other at engagement range or in the far field. One-to-one pixel comparison of these target scenes allows degradation of target contrast caused by propagation effects between the near-field and far-field positions to be quantified. Temporal changes of inherent signature can be quantified by monitoring the changes in the near-field imagery. The real-time image processing techniques, proof of principle guidelines, and several applications of the methodology are detailed.

A low focal ratio (f/l.8) visible range (350 nm to 750 nm) spectrograph containing an aberration-corrected concave holographic grating and a 512-channel linear array image sensor has been designed for use in an in-water spectroradiometer. A ray-trace analysis using different input wavelengths has been made, so as to optimize and assess the optics. The design analysis also includes calculations on the expected resolution, system etendue, and the simulated response of the complete system to a known in-water spectrum. The modular design concept of the spectrograph can be exploited by using it as a basic building block for other spectral measurements in the ocean.

An automatic ellipsometer that uses a four-detector photopolarimeter (FDP) to measure the state of polarization of light reflected from an optically isotropic or anisotropic, depolarizing or nondepolarizing sample surface is described. For conventional ellipsometry on specular isotropic surfaces, the incident light is polarized (at least partially) in one stable state (e.g., using a linear polarizer that need not be perfect), and the reflectance and ellipsometric parameters of the surface are encoded onto and, hence, can be retrieved from, the Stokes parameters of the reflected light. The latter are measured, virtually instantaneously, by the FDP. The FDP also greatly simplifies generalized Mueller-matrix ellipsometry on anisotropic or nonspecular surfaces. In this case, the polarization ofthe incident light is controlled by a linear polarizer followed by a quarterwave retarder (QWR) with a rotationally adjustable fast axis azimuth C. Fourier analysis of the output current vector of the FDP as a function of C yields a series of five terms whose vectorial coefficients determine the Mueller matrix column-by-column. In such an analysis, we account for the small inevitable imperfections of the QWR. Results are presented for measurements at the 633-nm wavelength of the ellipsometric parameters of a Au surface and the zeroth-order Mueller matrix of the 1200 G/mm Alcoated holographic grating for three different orientations of the grooves relative to the plane of incidence.

The use of transmission gratings with grazing-incidence telescopes in celestial x-ray astronomy is reviewed. The basic properties of transmission grating spectrometers and the use of "phased" gratings to enhance the diffraction efficiency are outlined. Special attention is given to the AXAF high-energy transmission grating (HETG) being fabricated at MIT. The HETG operates over the range 0.4 to 8 keV, gives resolving powers of 100 to 1000, effective areas of 10 to 300 cm², and a minimum detectable line flux of 1 to 10 x 10^-6 photons cm^-2 s^-1. The instrument consists of a single array with two types of membrane-supported grating facets: medium-energy gratings (0.6-μm period, 0.5-μm-thick silver) mounted behind the outer three AXAF mirrors, and high-energy gratings (0.2-μm period, 1.0-μm-thick gold) mounted behind the inner three mirrors. The materials and thicknesses are selected to maximize efficiency throughout the energy band. The facets are fabricated at MIT using a process involving x-ray lithography. AXAF will also carry a low-energy transmission grating (LETG) supplied by the Laboratory for Space Research at Utrecht. It uses mesh-supported grating facets of 1.0-μm period and is optimized for operation down to 80 eV. Gratings are most effective for the study of point sources, but they also give moderate resolution spectra of slightly extended sources and can be used to map the spatial distribution of line-emitting regions.

A rotation-invariant correlation filter to minimize correlation plane energy and produce a sharp and easily detected peak is addressed. The filter uses symmetry requirements to achieve rotation invariance and hence is generalized. Full mathematical detail of the filter synthesis and initial test results are presented. Drawbacks of the existing circular harmonic function (CHF) and other rotation-invariant filters are noted and used as motivation for these new filters.

Refinements of holographic instruments for the First International Microgravity Laboratory Spaceflight, scheduled for February 1992, are described. The refinements include addition of holographic optical elements (HOEs) to incorporate tomographic analysis of the solution concentration and particle image displacement velocimetry to measure convection. A variety of advanced diagnostic instruments were designed for future spaceflights and possibly in the space station. These new instruments employ fiber optics, diode lasers, and HOEs to enhance miniaturization and ruggedness and to reduce power requirements. The instruments can measure concentration, temperature, convection, and crystal growth rate. Instruments currently in use as well as the conceptual designs and applications of future laser- and holography-based instrumentation are described.

Waveguide holography (WGH) as an improved technique for display holography is discussed. The feasibility of reconstruction of waveguide holograms with white light is presented. Experimental results and future applications for waveguide holograms are also given.

An optoelectronic interconnection based on volume-holographic coupling elements located on a thick light-guiding glass plate has been realized. Diode lasers and pin diodes were used as optoelectronic converters. The holographic coupling elements were recorded in dichromated gelatin and aligned on the surface of a glass plate. The light was guided by total internal reflection inside the glass plate. The system performance has been tested at a data rate of 500 Mbit/s per channel. A total loss of 2.6 dB in the optical system and a signal to noise ratio of more than 28 dB were measured.

A simple method for making a true color rainbow hologram of a two-dimensional image with one wavelength laser is presented. The advantages of this method are its simple optical arrangement, high energy utilization, high fringe visibility, and large horizontal viewing angle. Satisfactory results are obtained and the problems of color reproduction are discussed.

This PDF file contains the editorial “Book Rvw: Fundamentals of Optical Fiber Communications," by Wim Van Etten and Jan Van der Plaats for OE Vol. 30 Issue 10

This PDF file contains the editorial “Book Rvw: Fiber Optic Sensors: An Introduction for Engineers and Scientists," edited by Eric Udd for OE Vol. 30 Issue 10