This PDF file contains the editorial “Editorial: Education in Optics” for OE Vol. 30 Issue 03

The near-real-time end-to-end evaluation of automatic target recognizers has been a reality in the laboratory environment for several years. Depending on the reliability of ground truth data, i.e., target location and sensor location in three dimensions and sensor pointing angle, field test evaluations could also be conducted at near real-time rates. End-to end evaluations, however, are inadequate for producing the quantity and quality of data needed for understanding both successes and failures of automatic recognition. The C2NVEO has developed a facility, called AUTOSPEC, for the expressed purpose of extracting intermediate data from processors. Once extracted, the data are stored in a relational database for subsequent analysis. The facility includes both the hardware and a number of software tools, developed at C2NVEO, designed to allow ready access to ground truth data, images, metrics, processor parameters, processor intermediate decisions, and processor final decisions. This paper presents the structure of the system and demonstrations of the tools developed.

The U.S. Army has a requirement to develop systems for the detection and identification of ground targets in a clutter environment. Autonomous Homing Munitions (AHM) using infrared, visible, millimeter wave and other sensors are being investigated for this application. Advanced signal processing and computational approaches using pattern recognition and artificial intelligence techniques combined with multisensor data fusion have the potential to meet the Army's requirements for next generation AHM. In a complex background scene the "problem" is as much one of clutter rejection as it is target detection. This work applies statistical pattern recognition approaches to background clutter characterization for target detection and identification. These techniques are used to evaluate a set of image metrics applied to infrared terrain clutter scenes.

Rotation-invariant image sharpening schemes based on Roberts operators, difference operators, Laplacian, and high-frequency emphasis are realized using optical symbolic substitution. Symbolic systems based on both optical content-addressable memory and phase-only holograms are considered for these image enhancement schemes.

Fully parallel processors call for a technology that is inherently parallel, a suitable number system, and an efficient encoding scheme for handling the data. The throughput of a binary adder/subtractor is limited by the carry propagation to the most significant bits. Optical adders using a modified signed digit (MSD) number system have been proposed to eliminate the carry propagation chain encountered in binary adders. The MSD number system satisfies the requirements of fully parallel addition/subtraction by limiting the carry propagation to two positions to the left. This enables one to carry out the addition/subtraction of two n-digit MSD numbers in three stages, independent of n. In this paper it is shown that by suitably exploiting the redundant nature of the MSD number system, the carry generation and propagation can be completely eliminated. The MSD adder/subtractor presented in this paper fully exploits the redundant nature of the MSD number system and performs the addition/subtraction of two numbers in a single stage. The adder employs 81 substitution rules to perform the addition/subtraction of two MSD numbers in a single stage. The number of substitution rules can be reduced to 16 if the input numbers are limited to binary. The proposed architecture reduces the computation time by 33.3% compared to the three-stage MSD adder originally proposed.

By applying finite impulse response filtering in conjunction with a median operation, the edges as well as the fine details in the input image can be preserved. The finite impulse response—median hybrid filter thus obtained is computationally more efficient and preserves both details and edges better than conventional median filters. The optical implementation of such a hybrid filter is discussed in this paper.

Several low-level vision algorithms have been implemented on a 16-node hypercube processor (AMETEK 5-14) by exploitation of its network embedding feature. This includes edge detection with the Sobel operator, histogramming, one-pass parallel binary image thinning, and noise cleaning. The primary objective is to parallelize these algorithms by achieving a proper image-to-processor topology mapping and to determine the actual speedup factor of parallel implementation over the sequential programming. Two basic topologies used are the ring and the nearest-neighbor networks, which are mapped onto the hypercube system. Several 512 x 512 gray-level images have been processed concurrently. A tenfold improvement in the speedup has been obtained compared to the sequential implementation in a single processor of the concurrent system. This result is obtained by ignoring the host-to-node, node-to-host, and I/O communications.

It is well known that telescopes magnify the image. However, it is not often mentioned that they also reduce the depth of field. Inverted Galilean telescopes obviously minify the object apparent size, but the depth of field is also increased. It has been observed that myopic persons wearing correcting noncontact eye glasses develop noticeable presbyopic effects at a later age than emmetropic persons. This effect may be explained by considering that the negative correcting lens and the positive myopic dioptric power of the eye together form an inverted Galilean telescopic system.

We solve the stereo correspondence problem by using extended edge contours as a source of primitives for structural stereopsis, as opposed to traditional point-based algorithms. Since an extended image feature conveys more information than a single point, its spatial and photometric behavior can be exploited to advantage. There are also fewer features to match, yielding a smaller combinatorial problem. The structural approach permits greater use of spatial relational constraints, eliminating the course-to-fine tracking of point-based algorithms. Solving the correspondence problem at this level requires only an approximate (probabilistic) characterization ofthe image-to-image structural distortion and does not require detailed knowledge of the epipolar geometry. This approach offers potential in automatically rectifying stereo images for which the camera geometry is known only vaguely a priori, the situation one encounters in aerial photography. Similarly, these techniques may be used to infer transformations between images of the same scene recorded by different sensors, at different times, but which are not precisely colocated in space, such as often occurs in aerial photogrammetry and remote sensing, as well as in mobile robotic navigation. We present experimental results in matching and calibration on real images using Laplacian-of-Gaussian (LoG) contour fragments as primitives in structural stereopsis.

Computer moire deflectometry (CMD) using one grating, a TV camera, and a computer image processor (CIP) is developed. The TV camera is located in a Talbot plane, allowing the recording of a (disturbed) image of the grating with maximum contrast and without any other optical component. CIP is used for obtaining, processing, and automated interpretation of the fringes. Double-exposure, real-time, time-average, and phase-measuring methods of CMD for transparent and reflective objects are demonstrated.

A three-mirror off-axis telescope was aligned by ray aberration measurement and reverse optimization, which is the technique of creating a computer model of the telescope in its misaligned state. A set of Hartmann measurements were made at multiple field points and multiple focus planes. The Hartmann data were then used as targets for the ACCOS V lens design code that created via least squares optimization a misaligned model of the telescope to match the measurements. The physical telescope components were then moved opposite the misalignments of the model. The Hartmann pattern was generated using a five-hole Hartmann screen and measured by the use of a position-sensing, lateral-effect photodiode. Our results show this method is a viable tool for assisting in the alignment of optical systems.

Various carbon black filled, cured rubber compounds were bonded by directing laser beams onto their interface. The strengths of laserinduced bonds were measured to be in the 10% to 50% range of strengths obtained with conventional thermal cure techniques. When the surface areas treated with the laser beam were substantially smaller than the areas of control samples, it was expected that bond strengths could be significantly increased. Binding times were impractically long (several h/cm²) but could probably be shortened through a better understanding of laser-induced binding mechanisms and a systematic optimization of laser characteristics.

The dependence of the extraction efficiency on the temporal variations in the quenching rate, absorption, and upper level formation rate is analyzed for rare gas halide lasers. The influence of these effects on laser output irradiance uniformity is significant, and it is shown that the optimum laser design is obtained by a compromise between maximum extraction efficiency and output uniformity. The results are presented in a parametric manner for general applicability.

A pulsed GaAs laser rangefinder is analyzed and designed. Expressions for background and signal power, noise, and signal-to-noise ratio are derived. The effects of pulse rise time, receiver bandwidth, and SNR on probability of detection and range accuracy are discussed. A computer simulation is used to optimize laser power, receiver aperture, and preamplifier bandwidth. A method ofthreshold detection is presented and discussed. Experimental results include receiver preamplifier transfer function and threshold detector performance.

The fabrication of laser beam apodizers (or soft apertures) with large clear apertures using cholesteric liquid crystals is described. A soft edge profile is achieved by filling a cell with two separate cholesteric liquid crystal mixtures with different selective reflection bands. The fluidlike property of liquid crystals allows them to mix at the interface. In this overlap region, the reflectivity changes as a function of position. This concept is applied to the fabrication of two devices: (1 ) a one-dimensional beam apodizer with a clear aperture that can be mechanically adjusted by sliding two complementary devices relative to each other and (2) a circular beam apodizer.

The development of an optical circuit that multiplexes gigabitper-second electronic data streams into a very broad bandwidth (greater than 10 Gbit/s) optical signal would greatly enhance interprocessor communications in a parallel computer. One possibility that we are investigating is coherence multiplexing. In this method, time delays exceeding the coherence time of the light source are used to achieve multiplexing. We have analyzed the limitations of coherence multiplexing for high-speed data links. For the geometry we are investigating, the analysis shows that the signal decreases inversely as the square of the number of channels. Noise sources include photon shot noise, excess noise (classical optical field fluctuations), and detector noise. A suitable optical source must have a smooth, broad spectrum. Superluminescent diodes or edge- emitting diodes are the best candidates. We show how all of these factors affect the total information transfer rate. An integrated optical circuit for coherence multiplexing is being designed and built. This device is an array of four Mach-Zehnder interferometers integrated on a lithium niobate substrate. The differential delays will be achieved using proton exchange. Each interferometer will have two sets of electrodes, one for signal modulation and a second for fine adjustments of the delay.

Molecules undergo Brownian rotational diffusion, continually tumbling through solution. If a molecule contains a fluorescent chromophore with an appropriate excited-state lifetime, and a solution of such molecules is excited with a brief flash of polarized laser light, then it is possible to measure the rates at which the molecule tumbles. One can measure the anisotropy of the decay of the fluorescence, a measure of the depolarization of the fluorescence in time. The rates of rotational diffusion are sensitive to the shape of the molecule. This paper examines the molecular shape information available from the anisotropy decay. Three systems, which are of interest to our laboratory, are described here. Our studies on the dye rose bengal (molecular weight ~1000) suggest that an approximation used in rotational diffusion theory—that the solvent molecules are very small compared to the solute—is valid even for this relatively small molecule. Next, we examine the effects of calcium concentration on the rotational diffusion ofthe protein calmodulin (molecular weight ~17,000) derivatized by photoinduced crosslinking to form a dityrosine fluorophore. In the presence of sufficiently high calcium ion concentration, this crosslinked calmodulin shows a single exponential anisotropy decay consistent with the rotational diffusion of the extended dumbbell structure found for calmodulin by x-ray crystallography. At low calcium concentrations, the crosslinked calmodulin rotates considerably faster, suggesting a much more compact shape; also, this anisotropy decay shows short correlation times that are interpreted as arising from a segmental flexibility not evident for crosslinked calmodulin at high calcium concentration. Finally, we examine a transition that is observed at very low salt concentrations for nucleosome core particles, relatively large complexes (molecular weight ~204,000) derived from the chromatin of higher organisms and comprised of eight histone molecules and 145 base pairs of DNA. The anisotropy decay of ethidium bound to the DNA indicates that core particles exposed to low ionic strength are considerably elongated relative to the shape at higher ionic strength.