On behalf of the officers and governors of SPIE, the SPIE editorial staff, and my predecessor, John Caulfield, I would like to thank all of the individuals who contributed in any way to the publication of Optical Engineering in 1985.

Optical Materials: An Introduction to Selection and Application-reviewed by Paul R. Yoder, Jr.; Optical devices and Fibers-Reviewed by S. Sriram; Fiber Fabrication-Reviewed by Felix P. Kapron; Lightwave Communications Technology: Part B: Semiconductor Injection Lasers, I; Part C: Simiconductor Injection Lasers, II, Light Emitting Diodes-Reviewed by James N. Walpole; Image Understanding 1984-Reviewed by James R. Bergen

Advances in the field of optical information processing continue to be impeded by a number of factors, the principal factor being the lack of highly sensitive, fast, high resolution, two-dimensional spatial light modulators. The performance limitations of these devices can be traced to inadequate materials properties as well as to inadequate exploitation of the characteristics of available materials.

We present an account of two recently observed nonlinear optical imaging processes, wavefront conjugation and infrared-to-visible image conversion, in liquid crystal films. We include discussion of dynamics, efficiency, resolution, aberration correction, and noise removal in these two processes.

Single-crystalline thin films of a new highly optically nonlinear organic material, N-(4-nitrophenyl)-(L)-prolinol (NPP), have been grown between transparent silica plates. Their calibrated thickness is 11 µm, but they can be made thinner or thicker with single-crystalline areas of the order of 10 mm2. Transverse second-harmonic generation measurements have evidenced the high efficiency of the material and allowed for the measurement of both the d21 and d22 coefficients. The value d21 = 200 x 10-9 esu is, to our knowledge, the highest phase-matchable coefficient ever reported for a material with transparency extending from 0.5 to 2 µm. The configuration explored here can be readily used, after minor modifications. for waveauided nonlinear interactions.

The n-i-p-i doping superlattices, periodic structures composed of n- and p-doped layers, possibly with undoped (i-) regions of the same semi-conductor material in between, form a new class of semiconductors. Apart from their two-dimensional and highly anisotropic electronic structure, a property they share with their compositional superlattice counterparts, they exhibit widely tunable electrical and optical properties that make them very appealing for various applications. Carrier concentration, lumines-cence spectra, absorption coefficient, and refractive index can be modulated by unusually large amounts by weak light signals, injection currents, or external fields. We briefly review the basic theoretical concept and some of the experiments that have confirmed the theory. Then we describe a number of optoelectronic and purely optical device applications. These include wavelength-tunable incoherent and coherent light-emitting devices with high modulation frequency, fast optical modulators, and nonlinear optical devices, possibly exhibiting optical multistability. Although the concept is applicable to any semiconductor that can be doped appropriately, a combination of periodic doping and composition ("hetero n-i-p-i") exhibits particularly appealing potential for devices in the 0.8 to 1.55 µm wavelength range.

An all-optical bistable device and an electro-optical bistable device, with performances approaching the fundamental statistical limits, are described. In the all-optical approach, the giant nonlinearities associated with bound excitons in CdS are exploited to demonstrate the lowest-switching-energy (< 4 pJ) all-optical bistable device. The device switches in less than 1 ns and fully recovers in less than 2 ns. These times are detector limited. A switching energy of less than 1 fJ is theoretically predicted for an optimized geometry. In the electro-optical approach, an InGaAsP/InP diode laser amplifier is used to demonstrate bistability with less than 6000 photons (< 8 X 10-16 J) incident on the device. The device switches in less than 1 ns and is cascadable since it has a gain of 100. It operates at room temperature and is compatible with diode laser sources.

The luminescence of a planar tunnel metal/barrier/metal (MBM) structure with a 40-A-thick Al2O3 dielectric layer under the action of short-pulse voltage and hf electromagnetic emission is investigated. The optical response is greater than 10 -3 W of light per watt of hf signal in the measurement range of 500 to 1200 MHz. The MBM structure can be used as a fast-operating visualizer of hf signals.

Coherent image amplification by two-wave coupling in a crystal of photorefractive BaTiO3 is analyzed. This amplifier is optimized with respect to such operational characteristics as gain versus amplified image quality and space-bandwidth product. Experimental results that demon-strate coherent image amplification of 4000, space-bandwidth product of 106, and gray-level dynamic range of greater than 100 are presented.

The analysis of volume diffraction gratings is important to the optimization of broad classes of devices, including acoustooptic Bragg cells, volume holograms, and spatial light modulators. A number of these devices involve gratings that exhibit striking polarization properties, which if used advantageously can offer significant opportunities for extended performance. Although the standard formalism for analyzing volume grating diffraction is the coupled wave approach, the optical beam propagation method has proven to be a powerful alternative formulation. For example, Thylen and Yevick recently utilized this method to study the coupling of polarized waveguide modes. In this paper, the optical beam propagation formalism of Thylen and Yevick for anisotropic media is further extended to the analysis of polarization effects in volume phase gratings. This method is both extremely intuitive (all intermediate mathematical steps have immediate physical significance) and also superior in cost of computation measures (execution time, computer memory required) for intricate modulation structures. Several broad classes of birefringent phase grating diffraction problems are identified, and sample solutions using the optical beam propagation method are exhibited. The cost of computation of the optical beam propagation method is shown to scale gracefully with increasing modulation complexity.

This paper presents a description of and design considerations for silicon/PLZT spatial light modulators (Si/PLZT SLMs), which provide high parallel processing power, dynamic range, cellular resolution, sensitivity, and the potential for implementation of "smart" optical devices. Following an overview of Si/PLZT SLMs, we discuss potential performance with respect to fundamental limits. We then review the current technology related to the development of these devices to meet the highest performance goals. Finally, we predict performance in specific applications. This analysis suggests that Si/PLZT SLMs can play an important role in the implementation of a variety of optical processing and computing systems.

A potentially high-performance, optically addressed spatial light modulator, called the photoemitter membrane light modulator (PEMLM), is being developed. The structure, operational theory, performance objectives and limitations, and experimentally observed performance of this device are discussed. A grid structure incorporated into the PEMLM is shown to significantly enhance the active removal of electrons from the membrane by secondary emission. The PEMLM offers the potential for framing rates in excess of 1 kHz, 50 1p/mm resolution, storage times of days, sensitivities of less than 1 nJ/cmz, and an intrinsic ability to perform such image processing operations as thresholding, contrast modification, image addition and subtraction, binary logic, and optical synchronous detection.

Preliminary x-ray imaging characteristics of a vacuum-demountable, x-ray sensitive, microchannel spatial light modulator are presented. The measurements include spatial resolution, x-ray exposure sensitivity, framing speed, and built-in image postprocessing capabilities. These results are presented together with a discussion of the principles of operation and the noise performance of the device in the high gain limit.

A technique for subtracting images in real time utilizing a single liquid crystal light valve (LCLV) is described. The two images are projected in registration on the LCLV through a common grating. The projections are chosen such that the grating's image due to one beam is complementary to that displayed by the second beam, thus generating an interlacing effect. The readout light beam is optically filtered, so that only different features in the two images are revealed. Experimental results are presented.

For the first time traceable transfer standards have been developed for measuring 1.064 µm laser pulses with duration of about 10 to 100 ns, peak power density of about 10-8 to 10-4 W/cm2, and energy density of about 10-16 to 10-11 J/cm2. These power and energy transfer standards use avalanche (APD) and PIN silicon photodiode detectors, respectively. They are stable and have total uncertainties of about 10%. The system for calibrating them and other devices consists of a cw Nd:YAG laser beam acousto-optically modulated to provide low-level laser pulses of known peak power and energy. With pulse height analyzer readout, the PIN transfer standard system may record each pulse, from which the mean pulse energy and laser stability may be evaluated. With integrating voltmeter readout, this system can measure energy or average power. These pulsed and cw measurement techniques can be extended to the visible and other near-infrared wavelengths.

A new optical testing method that is potentially useful for measuring spherical aberration is introduced. It is a noninterferometric technique that involves making use of axial intensity information.

Two-dimensional data such as photos, x-rays, various types of satellite images, sonar, radar, seismic plots, etc., in many cases must be analyzed using frame buffers for purposes of medical diagnoses, crop estimates, mineral exploration, and so forth. In many cases the same types of sensors used to gather such samples in two dimensions can gather 3D data for even more effective analysis. Just as 2D arrays of data can be analyzed using frame buffers, three-dimensional data can be analyzed using SOLIDS-BUFFER memories. Image processors deal with samples from two-dimensional arrays and are based on frame buffers. The SOLIDS PROCESSOR system deals with samples from a three-dimensional volume, or solid, and is based on a 3D frame buffer. This paper focuses upon the SOLIDS-BUFFER system as used in the INSIGHT SOLIDS-PROCESSOR system from Phoenix Data Systems.

The local statistics of an image are needed, for example, to transform the input into stationary data for which many standard enhancement/coding algorithms are optimized, as well as to implement locally adaptive processing techniques. We discuss a system that uses a flying window scanner to extract the second-order parameters (local mean, variance, and correlation length) in real time and show how these parameters can be used to transform an input into block stationary data. The same scanning system is also applied to the measurement of a variety of histograms in a single frame scan.

Design and fabrication considerations for multielectrode modulation in a single acousto-optic device operating in the near acoustic field are presented. In particular, topics including acoustic and electrical cross-talk and electrode apodization to control Fresnel effects of the sound column on diffracted light are discussed; a concept of nesting electrodes to create overlapping laser beams is introduced.

Free-space optical communication systems using laser diode transmitters exhibit data rate limitations imposed by the diode's relatively low average output power. Incoherent power combiners represent a viable method for circumventing this limitation. A polarization beam combiner is described, and overall performance is analyzed in terms of signal extinction ratio and total transmitted power. It is shown that in such a combiner it is possible to increase the total transmitted on-axis far-field intensity, but the signal extinction ratio remains constant. The combiner system's true performance is calculated using polarization and power data for different types of laser diodes.

An experimental procedure is described for determining how hot photographic film becomes when subjected to the IR presensitization process. Correlations with deposited IR energy and film density are also made.

Reflecting and catadioptric lenses have been used in astronomical telescopes for many years. More recently, among other applications, they have been widely used in large-aperture and man-portable image-intensified night vision equipment. The afocal telescope used with a scanning infrared system operating in the 8 to 12µm wave-band is required to match the large field of view and small aperture of the scanner with the small field of view and large entrance aperture required for long-range observation. The telescope construction used is usually a refracting telephoto. This can be configured either as a single field of view lens, as part of a dual or multiple field of view switchable system, or as the basis for a mechanically or optically compensated zoom system. However, for large, high magnification telescopes, catadioptric systems can offer advantages over refractors. Two types of catadioptric lens are described. The first has a "low" magnification (7.5 x ) and utilizes a full aperture germanium lens to correct spherical aberration. The second has a "high" magnification (30 x ) and uses a subaperture germanium element to correct the same aberration.

The construction of airborne observatories, high mountaintop observatories, and space observatories designed especially for infrared and submillimeter astronomy has opened fields of research requiring new optical techniques. A typical far-IR photometric study involves measurement of a continuous spectrum in several passbands between ~30 µm and 1000 µm and diffraction-limited mapping of the source. At these wavelengths, diffraction effects strongly influence the design of the field optics systems that couple the incoming flux to the radiation sensors (cold bolometers). The Airy diffraction disk for a typical telescope at submillimeter wavelengths (~100 um to 1000 um) is many millimeters in diameter; the size of the field stop must be comparable. The dilute radiation at the stop is fed through a Winston nonimaging concentrator to a small cavity containing the bolometer. The purpose of this paper is to review the principles and techniques of infrared field optics systems, including spectral filters, concentrators, cavities, and bolometers (as optical elements), with emphasis on photometric systems for wavelengths longer than 60 µm.