Since the discovery of the liquid crystal phase in 1888, research in this intermediate state of matter and its fascinating optical phenomena has experienced several periods of intense interest. However, there was no large-scale application of liquid crystal technology until the 1970s, when the advent of microelectronic digital circuits during the 1960s created a need for low power, compact display devices for certain portable electronic products. Thus, the announcement in 1968 of the dynamic scattering liquid crystal display (LCD) triggered a great interest in the electronics industry and dramatically increased research activity on liquid crystal materials and their electro-optic effects. Within a few years these efforts led to the invention of the twisted nematic LCD and the discovery of several classes of stable liquid crystal compounds. These developments significantly improved the performance of the LCD such that by the mid 1970s the twisted nematic device became the dominant display used in electronic watches and calculators.

This review paper describes the development of laser-addressed liquid crystal display (LLCD) technology. It covers a period dating back to 1970 and includes the work of all research groups who have published their results in this field. The technology employs a scanned laser beam to thermally write on a high-resolution liquid crystal light valve. The LC cell has storage but can be erased rapidly with an electric field, and an image may be modified using selective erase and rewrite. The cell is projected onto a screen to give a bright, high-contrast and high-information-content image. Being a projection display, a wide range of screen sizes is possible, and color can be provided by overlaying multiple images.

This paper will discuss developments in liquid crystal (LC) television displays, mainly for pocket-size TV sets. There are two types of LC television displays. One is a simple multiplexing type, and the other is an active matrix type. The former type is an easier way to fabricate large and low-cost LC panels than the latter. However, it has serious drawbacks. The contrast gets lower as the duty ratio gets higher. Therefore the TV image of this type inevitably has rather low contrast and resolution. On the other hand, the active matrix type, which consists of active elements in each pixel, has several advantages in overcoming such problems. The metal oxide semiconductor transistors and the amorphous or polycrystalline Si thin-film transistors (TFTs) have possibilities in this application. A full-color LC display, which can be realized by the combina-tion of color filters and poly Si TFT arrays on a transparent substrate, was proven to have excellent color image, close to that of conventional CRTs. Here, several examples of LC television displays, including color, are shown. Some of them are already on the market, and others will be soon.

Basic principles applicable to color liquid crystal displays (LCDs) are summarized, and various types of color LCDs are reviewed. Among these LCDs, the one with microcolor layers of the three primary colors is most promising for general applicability. The characteristics, problems, and subjects for the future study of this LCD are summarized.

A thermal-electric effect that modulates the absorption of a dichroic dye-smectic A mixture and a display based on such an effect are described. The physical principles behind the optical and thermal performance, the memory effect, addressing schemes, and other major practical issues related to the display's operation are discussed. Experimental data and typical values for various display parameters are presented.

We present numerical solutions of the equation of motion that governs the dynamics of molecular orientation in ferroelectric liquid crystals (FLCs). The obtained solutions illustrate novel electro-optic effects in FLCs. Specifically, we treat the switching by an applied electrical pulse between two optically distinct stable states, and calculate the requisite pulse width for switching as a function of pulse amplitude. We also show that with appropriate liquid crystal cell preparation, switching between four distinct states is feasible.

There has been an explosive growth in the use of digital images in disciplines such as medicine, astronomy, computer design, industrial inspection, and biology, to name a few.

Equations for the diffraction-limited resolution of laser scanners are developed to encompass all known forms of angularly deflected systems. This includes the polygon (pyramidal or prismatic) with or without optical power in its elements (such as lenticular or holographic), whether overillumi-nated or underilluminated, forming output beams that are collimated, con-vergent, or divergent, with outputs normal or nonnormal to the rotating axis, exhibiting arbitrary displacement from the mechanical fulcrum (including zero), and operating with arbitrary ratio of optical-to-mechanical scan angle. Resolution is expressed completely at the deflecting element, requiring no determination of image spot size, and unless aberrated or vignetted, is inde-pendent of subsequent passive optics.

Modulation transfer function (MTF) and pseudo-MTF analytical techniques are applied to the problem of predicting system performance for reconnaissance sensors that incorporate charge-coupled device (CCD) imaging detectors. The MTF analyses, used in conjunction with assumptions about signal-to-noise (S/N) requirements and a simplified weather model, provide a much-needed systems design tool.

A variable format laser scanner and plotter system has been devel-oped. By using a galvanometer to move the laser beam, the scan amplitude can be adjusted so that only the area of interest is scanned and digitized. Compared to other scanning methods (i.e., spinning polygon and rotating drum), this leads to efficient use of memory, drastically reduced data rates, and increased resolu-tion at high magnification. The machine is capable of scanning a 20X24 in. area at 1500 lines per inch in 4 min. Optical encoders are employed on both scan axes to ensure geometric accuracy. The system is microprocessor-con-trolled, with the operator interface through a CRT, keyboard, and menu-type software. Scanning and plotting are done in daylight with automatic roll film loading and processing.

Various types of permanent hardcopy images consisting of dots or raster lines can be output from the same scanner because it writes a fixed-pitch dot. The machine is easy to use and can stand alone or can be interfaced to other image processing equipment.

The goal of neuroscience is to understand how different parts of the brain are wired together and how they communicate with one another. Several recently developed techniques use a method known as autoradiography to create images of brain connectivity and function. These autoradiographic methods promise to be quantitative and comprehensive. HoweVer, the data appear as gray scale images, which presents certain data analysis problems. Through a collaborative effort between neuroscientists, engineers, and com-puter scientists, we have developed a computer-based quantitative image analysis system. We have designed an interactive menu-driven software pack-age. Our objective was to allow neuroscientists to quantitate, tabulate, and interpret the image data collected on autoradiographic files. A description of the hardware, the software package, and its application is presented.

A new method has been developed to apply image processing tech-niques to a more conventional stereoscopic measurement method. This new technique will provide both qualitative information and quantitative data, which are needed to achieve a better characterization of complex flow fields such as those in agitated vessels. The technique of flow visualization has been widely used to acquire qualitative realizations of flow structures and mixing mecha-nisms. However, the quantity of data obtained from such flow visualization studies has always been limiting. Sheu et al. [Chem. Eng. Comm. 17, 67 (1982)] used a stereoscopic cine camera to record the flow field in an agitated tank containing small, neutrally buoyant tracer particles and showed that three-dimensional velocities can be obtained from discrete sets of particle locations in stereo scenes. In this paper, the application of digital image processing to automate data acquisition procedures is presented. Instead of tracking particles manually, films (visual images) were digitized and were stored in digital form on magnetic tapes. A software package, utilizing THRESHOLDING and PATTERN MATCHING, has been developed to perform the following tasks: (1) particle image identification, (2) particle image tracking in consecutive frames, (3) stereo pair matching of particle trajectories, and (4) velocities evaluation in three-dimensional space evolving in time. The important attributes for flow characterization, such as velocity, acceleration, turbulent intensity, and possi-bly temperature, can be collected for analysis in much larger quantities at a much faster rate than ever before. Furthermore, considerable improvement in accuracy over that of a manually tracked method is also achieved. Most attrac-tive of all, this new combination of image processing and stereoscopic motion pictures is capable of providing sufficient data with high resolution to character-ize the flow field from a Lagrangian/Eulerian point of view.

In the application of bilevel digital display and electronic print-ing, threshold setting is used to get binary images from optical scanning digitizers. Such images can be simply obtained from a raw continuous-tone image by using a fixed threshold. However, due to (1) a wide range of background colors, (2) wide variations of density in the printed infor-mation, and (3) the shading effect caused by imaging optics, adaptive threshold setting is obviously needed for obtaining high-quality displays and hard copies. This paper will review both known and newly developed adaptive threshold techniques. Simulated test patterns were used to make the comparison quantitatively. The techniques that will be re-viewed include the fixed threshold, peak and valley detector, gradient detector, fractional average context, transition-refreshed peak and valley detector, and robust two-dimensional adaptive thresholder. Among them, the last technique is found to perform very robustly in the presence of shading as well as text density variation. Specifically, both objective and subjective evaluations of pictorial results from this tech-nique have indicated that text with a differential density as low as 0.15AD is detectable with background shading variations as much as 0.30D (50%).

Teflon polishing is capable of producing surfaces flat to 3 nm or better, but its wider application requires suitable testing methods to measure such small residual errors. Digital interferometry solves this problem and, because data can be stored and processed, makes it possible to carry out a variety of tests with high precision. The application of these techniques to the production and testing of a solid Fabry-Perot eta Ion with a diameter of 50 mm, a thickness of 0.352 mm, and a maximum deviation from parallelism of its faces of ±2 nm over the central 30 mm is described.

A deterministic model-based restoration procedure is presented. The algorithm is effective for the restoration of coarsely sampled images degraded by diffraction and noise. The a priori information, an assumed parametric object model, is used to arrive at the solution. The object model is convolved with the optical system and sensing mechanism degradations and then matched against the limited number of available samples. The unknown parameters are then estimated using a numerical least mean square error optimization procedure. The method has been tested with a double delta function model via digital simulations. A zero-mean, additive, white Gaussian background noise process was assumed. The technique requires a high signal-to-noise ratio (SNR) to resolve the doublet with a separation distance smaller than the detector width. With increasing separation, good restoration can be achieved at low SNR. The procedure is applicable to restore generalized objects.

This paper describes an image processing system that is in operational use for the extraction of latent information from degraded photographs arising in routine police work. A wide range of spatial domain and Fourier domain techniques to both diagnose and correct for various picture problems are described. The enhancement methods discussed include contrast enhancement, noise filtering, digital color filtering, perspective correction, adaptive Fourier filtering to remove background patterns, and image deblurring. Color images are treated by operating on the separated red, green, and blue (R, G, B) components, and a novel encoding scheme is used to enable the display of color pictures on a standard 8-bit frame store. These techniques have been developed for, and applied to, operational rather than laboratory-generated images. A brief description is given of the hardware that is used, which incorpo-rates an array processor to enhance computational speed, a high quality micro-densitometer for digitizing images, and a digital frame store for final display. The system has been configured to give an operator as much interactive control as possible.

Interferometric sensors traditionally have been limited by their non-linear input-output characteristics. This paper presents a method for output linearization using four interferometer outputs corresponding to ±sin ct and ±coscp, where 4 is the relative phase of interferometer legs. These outputs are combined in an arctangent algorithm to extract (/). Applications to both Mach-Zehnder and Sagnac interferometers are discussed, with experimental data from a fiber gyro presented. The data taken over a 47r range of 4 demonstrate linearity and stability of the algorithm.

A frequency domain implementation of an optical transversal processor has been described previously. Since this system uses Bragg cells both as the delay line and as the accumulators that provide the tap weights, a key question concerns the effect the finite integration times have on the perfor-mance of the system. Computer programs were written to simulate an adaptive notch filtering application; the measure of performance is the correlation coefficient for the residual signal and the desired received signal. The correlation coefficient was increased significantly by tapering the accumulators so that the readaptation phenomena caused by large values leaving the accumulator are minimized. Several examples of the performance are given as a function of the number of taps, the length and degree of taper of the accumulator, the feedback gain, and the number of iterations. The results show that a finite accumulator is not a serious drawback, particularly for those applications in which the system must operate in a rapidly changing environment. The performance of the system then approaches that of one having an infinite accumulator with the gain adjusted to give equivalent tracking performance.

A high stray light cryogenic telescope has been developed to provide spatial definition for a Fourier transform spectrometer. The system is all-aluminum and uses off-axis superpolished parabolas with an advanced baffle system for high stray light performance at cryogenic temperatures. The all-reflective optical system is capable of better than 0.1 mrad resolution over a half a degree field of view. The brazed mechanical structure is integrated with a careful thermal design, allowing the optics to maintain liquid helium region temperatures without the use of thermal straps. The telescope has been tested for stray light, optical performance at cryogenic temperatures and against shuttle environmental requirements. A discussion of the design analyses, test techniques, and measured results will be included in the paper.

Multiple quantum well AI,Ga1-xAs/GaAs structures grown by molecular beam epitaxy were studied in order to determine the growth conditions that optimize luminescent response. Low temperature photolumines-cence results indicate that a growth temperature of 700°C is optimum. The quality of the interfaces between the AlxGa1-xAs and GaAs layers was assessed by means of modulation doped structures. It was found that the interfacial quality is optimized at a growth temperature of 700°C. Finally, room temperature continuous wave photopumped laser operation at a wavelength of A= 7270 A is demonstrated in these structures.

Laser calorimetry has been widely used to measure thin-film optical absorption in filmed substrates with total film-substrate system absorptance of 1 x 10-2 and below. This paper will discuss the advantages and disadvantages of the various types of calorimeters presently used to measure witness-size samples in the absorptance range of 1 x 10-2 to 1 x 10-5. Special emphasis will be given to single-layer films. Considered will be the implications of front versus back surface films, film thickness, film-substrate interface absorption, and laser coherence on the interpretation of the measured total absorptance. Throughout this paper, the main concern will be the errors present in calorimetric measurements.

The optical design of a multichannel sight for use in an armored vehicle used in an air defense role is described. Emphasis is placed on the interaction and incompatibilities among the various optical channels and the resolution of conflicting requirements.

The slow-scan television camera being built for NASA's Galileo Jupiter Orbiter spacecraft consists of a 1500 mm focal-length telescope coupled to a camera head housing a newly developed 800 x 800 element charge-coupled device (CCD) detector based on "virtual-phase" charge transfer technology. This detector results in a broadband sensitivity over 100 times that of a comparable vidicon-tube camera while also yielding improved resolution, linearity, geometric fidelity, and spectral range. In the near-Jovian radiation belts, interactions of high-energy particles with the silicon CCD result in the production of unwanted charge, and special techniques have been implemented (e.g., tantalum and quartz shielding, rapid image readout, and 2 x 2 picture-element on-chip averaging) to ensure adequate signal-to-noise performance for images acquired as close to Jupiter as five planetary radii. The images returned from Galileo will provide high-resolution (approximately 1 km) mapping coverage of most of the surface of the four large Galilean satellites of Jupiter with coverage of selected targets at resolutions as good as about 20 m. The broad spectral range of the instrument (0.4 to 1.1 Am) and the use of special methane-absorption-band filters in the near-infrared will allow study of the Jovian atmospheric structure and dynamics. Excellent off-axis light rejection and high sensitivity of the instrument will permit study of low-light-level phenomena such as lightning and aurorae on Jupiter and the Jovian ring.

There are three basic thin-film growth modes: Volmer-Weber (island), Frank and van der Merwe (layer), and Stranski-Krastanov (layer followed by island). Examples of these growth modes and variations thereof are presented, and the theories governing the initial and later stages of growth in each case are reviewed. Some useful applications of the theories are also given.

I have often noted that the most important contributors to a journal usually go unnamed. These are the referees. They contribute their expertise free and with little thanks. Indeed, they often suffer some real abuse from the authors. There follows an honor roll of people who have helped me to referee Optical Engineering prior to 1984. If I have missed your name through clerical error, please (1) forgive me and (2) let me know.