We describe a multifunction nonlinear optical processor that can perform various types of operations such as image deconvolution and nonlinear correlation. This processor is joint power spectrum based and does not use any filters. In this technique both the input signal and the processing function are displayed side by side at the input plane of the processor. The joint power spectrum of the input signals is thresholded with varying nonlinearity to produce the specific operation. In image deconvolution the joint power spectrum is modified and hard clip thresholded to remove the amplitude distortion effects and to restore the correct phase of the original image. An amplitude mask averaged over an ensemble of images is assigned to the thresholded power spectrum to provide the amplitude magnitude of the restored image. In optical correlation, the Fourier transform interference intensity is thresholded to provide higher correlation peak intensity and a better defined correlation spot. We show that various types of correlation signals can be produced simply by varying the severity of the nonlinearity and without the need to synthesize the specific matched filter. For example, a phase-only correlation signal is produced by selecting the appropriate nonlinearity. An analysis of the nonlinear processor for image deconvolution is presented. Computer simulation of the proposed technique for a linearly smeared image is provided.

Associative memory and pattern recognition systems have many similarities. Autoassociative memories can be viewed as image restoration, and heteroassociative memories as classification or feature extraction systems. Connectionist, or neural network, architectures are well suited to perform associative memory operations. The predominant calculation in these systems is vector-matrix multiplication. While requiring 0(N2) operations on a serial machine, a simple optical architecture can perform this calculation in nearly constant time. We have demonstrated an optoelectronic connectionist module with modifiable inputs and weight matrices that performs associative memory operations. The weight matrix can be generated with or without the optical hardware, providing a testbed for simulations of physically implemented connectionist systems. Low cost commercial liquid crystal television sets are used to encode unit activities as intensity of linearly polarized light and signed multiplication as rotation of this light. Integrated computer control allows the extension to many connectionist models.

An all-optical holographic memory was recently proposed by researchers at the Hughes Research Laboratories. This paper details the investigation into the characteristics of that system and an extension to a position, scale, and rotation invariant (PSRI) holographic associative memory. The PSRI feature space is the en-polar representation of the square magnitude of the Fourier transform, IF(fnr, fo)I2, of the objects. This representation is generated optically using a coordinate transform computer-generated hologram. Angularly multiplexed, diffuse Fourier transform holograms of the PSRI feature space are characterized as the memory unit. Distorted input objects are correlated with the hologram, and a nonlinear phase conjugate mirror, self-pumped BaTiO3, reduces cross-correlation noise and provides object discrimination. The self-pumped phase conjugate mirror is characterized, and high diffraction efficiency bleached holograms are used in the place of thermoplastic film. Applications of the memory are also presented.

Engineering guidelines are presented for selecting and implementing a method to optically restructure a damaged detector. Under certain conditions, undamaged areas of a detector can be coalesced to maintain recording continuity of a two-dimensional object scene with minimal loss of total detector area. This goal can be achieved by using relay lenses in specific arrangements and in some cases by locating a biprism or a coherent fiber bundle near an image surface. Optical correction and performance are identified with the parameters of detector and damage sizes.

High power laser beams tend to have highly asymmetric irradiance distributions across their pupils. However, there are applications for these lasers requiring uniform irradiance distributions on a target of interest. A strip mirror integrator provides a practicable scheme for achieving this uniformity without significant power loss.

Architectures for focal plane image processing are discussed. On-chip image preprocessing for solid-state imagers using analog CCD circuits is described for low, medium, and high density detector arrays. A spatially parallel architecture for low density, high throughput applications is described. For sparse illumination or event detection, a content-addressable architecture is proposed. A new pipelined vector pixel processor architecture for medium density infrared staring focal plane arrays is described. Neighborhood reconstruction during serial readout of high density TV-quality imagers for a pixel processor is considered using delay and analog frame memory techniques. The potential of on-chip read/write analog frame memory for image transformation and frame-to-frame processing is discussed.

A double spectral image sensing device has been developed for industrial tasks. The device comprises a common objective shared by two bidimensional CCD detectors that see the same field of view by means of a 50-50 beamsplitter and a mirror. Proper adjustment of the optics and of both detectors, one with respect to the other, yields two almost identical images at the output of the detectors. If limited bandwidth interference filters are inserted in front of each detector, many useful applications arise, such as robot welding vision, pyrometry in the range 820°C to 1350°C, and surface inspection.

The synergistic combination of ladar and infrared information allows segmentation of images of real scenes containing objects in the presence of clutter. Log-transformed range gradients from the ladar image are subjected to a threshold test and then processed through a nearest-neighbor filter to segment the images. The combination of processed ladar and forward-looking infrared images subsequently can be used for object identification. Analysis of the range-gradient-based segmentation method is given, and results are shown.

The performance of focal plane arrays of cadmium mercury telluride (HgCdTe) photodetectors when used in the 8 to 12 um spectral range is limited by the nonuniformity of the responses of the detector elements in the array. If arrays of large numbers of detectors are to be used as sensors to achieve small noise equivalent temperature differentials (NETDs), these nonuniformities will have to be reduced during the fabrication of the arrays or compensated for in operation by correcting the output obtained from each individual detector. This paper analyzes some of the requirements for compensation techniques and discusses their application to infrared focal plane detector arrays. A method of compensation is proposed that provides significantly better correction than linear two-point correction schemes. The performance of the method is analyzed, and its application is demonstrated using a HgCdTe focal plane detector array.

We describe a 3-D vision system designed and constructed at the Technical Research Centre of Finland in cooperation with the University of Oulu. The system was developed chiefly for geometric measurements of large objects. The system has been operative for about one year, and its performance has been extensively tested. The system consists of three main units: the range finder, the scanner, and the computer. The range finder is based on the direct measurement of the time-of-flight of a laser pulse. The scanner consists of two mirrors driven by moving iron galvanometers; this unit is controlled by servo amplifiers. The computer controls the scanner, transforms the measured coordinates into a Cartesian coordinate system, and serves as a user interface and postprocessing environment.

We study the imaging performance of hololenses formed with four different geometries through an analysis of their third-order aberration coefficients. It is found that the geometry proposed by Brandt [Appl. Opt. 8(7), 1421-1429 (1969)] gives the least residual aberration with minimum variation of this aberration with the reconstruction angle. When the ideal position of one of the construction beams is changed in order to generate a hololens array, the residual aberration is found to increase sharply, which in turn affects the image resolution among the multiplied images in the output. We have generated a hololens array using Brandt's geometry with the help of a 1-D sinusoidal grating. The results of multiple imaging with the hololens array are presented. The image resolution is reasonably high and can be further improved by reducing the f-number of the hololenses.

A new semiconductor device, the gate-controlled photodiode (GCPD), has been experimentally demonstrated. A two-dimensional (2-D) GCPD array may fulfill the combined function of a 2-D spatial light modu-lator (SLM) and a photodetector array in some applications. Its high parallelism, simplicity, and compatibility are attractive for optical signal processing and computing, optical interconnection for VLSI circuits, and artificial neural networks. Some typical applications for optical computing are discussed.

High performance holograms are a crucial part of realizing the predicted benefits of optical interconnection of electronic circuits. Fabrication of computer-generated holograms using electron-beam lithography provides access to the needed performance but presents new challenges in design, encoding, and data handling. Two holograms are described that represent different approaches in each of these areas. The first hologram connects a single laser source to several widely separated detectors. A paraxial imaging arrangement allows the holographic interferogram to be encoded as concentric circles of a Fresnel zone plate. The second hologram was designed to replace the row address lines on a 1 kbit RAM chip. In this case, broad separation of the sources prohibits use of the paraxial approximation. Instead, a piecewise approximation to the optimal phase function is encoded with a closed-contour fringe-tracing algorithm. Both holograms were evaluated in experimental systems involving photodetectors integrated onto a VLSI circuit chip and a discrete semiconductor laser.

In laser Doppler vibrometry of sinusoidal vibration, direct analysis of the photodetector output or the heterodyne signal using a spectrum analyzer is emphasized. A technique utilizing the spectra at the carrier frequency and the first sideband is proposed for unambiguous analysis of the vibration amplitude. Experimental results demonstrate the validity of the proposed technique.

The techniques of high resolution moire photography and high speed photography have been combined to allow simultaneous measurement of both in-plane components of a transient displacement field with microsecond time resolution. A 150 lines mm-1 specimen grating is imaged onto a reference grating with a specially modified camera lens. The resulting real-time moire fringes are recorded with a high speed image converter camera. An automatic fringe analysis technique based on the 2-D Fourier transform method is used to extract the displacement information from the high speed sequences. The techniques are illustrated by the results of an investigation into the transient deformation of polymethyl methacrylate caused by solid particle impact.

Discovery of two mathematical errors in the paper "Optical flatness standard" by W. Primak, published in Optical Engineering 23(6), 806-815 (1984), is described, and the reader is referred to a sequel giving the corrected results.

As some of you already know, Martha Stockton, the Associate Editor of Optical Engineering, is quite ill. For several months now she has been undergoing radiation and chemotherapy treatments, which have slowed her down just a bit in the performance of her editorial duties and have restricted her many other activities. She recently asked me if I could find someone to help her out with some of the routine aspects of the job, and II am in the process of locating an individual to do so.

Optical Techniques for Industrial Inspection is a well-organized and comprehensive summary of modern inspection methods for a wide cariety of applications. This book provides a good introduction to the large and rapidly expanding field of optical monitoroing and process control. It should serve as a useful guide and reference for students or others new to this field, for instumentation engineers who may be unfamiliar with optical techniques, or for optical engineeers who need to solve certain process monitoring problems.