Richard V. Johnson

Polarization properties of enhanced self-diffraction in sillenite crystals

Doppler-enhanced self-diffraction in two-beam coupling experiments with sillenite crystals exhibits pronounced optical polarization effects due to the concomitant presence of natural optical activity and electric-field-induced linear birefringence. Coupled wave equations that describe the polarization properties, exclusive of self-diffraction effects, have previously been derived for the two principal crystal orientations most commonly used in photorefractive recording. In this paper, the coupled wave equations are combined with a linearized model of the photorefractive recording process (single trap level, single mobile charge species) to analyze the impact of self-diffraction effects on the polarization state evolution. Numerical solutions of these equations yield optimum configurations for enhanced gain and improved image contrast in two-wave mixing with such materials. In addition, inclusion of optical activity in the model emphasizes the contribution of this effect to the apparent reduction of the effective electrooptic coefficient of bismuth silicon oxide crystals.

Scophony Spatial Light Modulator

An alternative to the conventional flying-spot scanner architecture is the Scophony scanner. The Scophony scanner uses the same optical elements as the more familiar flying-spot scanner: a rotating polygon mirror, an acousto-optic (A/O) modulator, and a laser light source. The flying-spot scanner is designed to construct its image a pixel at a time; no more than one pixel is illuminated at any given instant. The Scophony scanner is designed to image a broad swath of the A/0 modulators acoustic pulses onto the photoreceptor. Many pixels are illuminated at any given instant in the Scophony scanner. The result is a scanner with a coherent imaging response. This coherent response implies that the phase of the modulators electronic drive signal for a given pixel profoundly influences the formation of the neighboring pixels at the scanner image plane. This coherent response enables electronic manipulation of the video drive signal to have significant impact on the optical imaging performance of the scanner. In this paper, two electronic manipulation schemes are pro-posed for doubling the resolution of the Scophony scanner, one scheme for analog video signals and one scheme for binary digital video signals. Each scheme gives superior contrast ratio performance when compared with the flying-spot scanner.

Temporal response of the acoustooptic modulator in the high scattering efficiency regime

An efficient and rigorous algorithm is proposed for analyzing the temporal response of the Bragg acoustooptic modulator in the high scattering efficiency regime. Computer studies of this model successfully predict pulse profile asymmetries that have been observed experimentally and cannot be predicted by the usual Greens function (small signal) models of the acoustooptic coupling. The technique of predistorting the electronic video signal by passing it through a nonlinear electronic network to linearize the modulator response is effective only for slowly varying video signals. Residual nonlinearities appear for rapidly varying video signals.

Scophony light valve

The optical modulator in a flying spot scanner converts the electronic video signal into a corresponding temporal modulation of a light beam. An alternative configuration, which directly exploits the spatial modulation of an acoustooptic cell, is the Scophony scanner, first developed by the Scophony Laboratories of London during the 1930s. The Scophony scanner responds like a coherent imaging system, whereas the flying spot scanner performs like an incoherent imaging system, when the light source is spatially coherent. The Scophony response is intimately linked to the concepts of FM blur and the deflector as video spectrum bandpass filter.

Temporal response of the acoustooptic modulator: geometrical optics model in the low scattering efficiency limit

A phenomenological model of the acoustooptic modulator is proposed. The temporal response of the deflected light power is a quadratic invariant function of the video signal amplitude. The two-dimensional response kernel is defined by an overlap integral of the incident light and sound field profiles, similar to a convolution operator. When the incident light is focused to reduce risetime, the light throughput efficiency and the deflected light profile degrade because the modulator is a linear filter with limited angular passband operating on the propagation angle spectrum of the incident light.

Laser Printing With The Linear TIR Spatial Light Modulator

A linear spatial light modulator has been developed for laser printing. It provides capability for parallel modulation of several thousand points across a line of illumination, which is then imaged onto a photosensitive medium. The spatial light modulator, which has been described previously, utilizes a VLSI silicon chip containing addressing electronics, drive transistors, and a series of metal lines. This chip is pressed against a single crystal piece of lithium niobate, so that flinging fields created by voltage differences between metal lines are proximity coupled into the crystal and generate locally controllable changes in the index of refraction. The device is read out in total internal reflection off the proximity coupling interface, with schlieren readout imaging optics used to convert the phase modulation of the wavefront to a modulated line image. This paper will review the basic device concept, describe some of the device design and operating parameters, discuss printer application considerations, and show results from a breadboard level printer.

Electronic Focusing In The Scophony Scanner

The Scophony Light Valve when used in a laser scanner exhibits a coherent imaging response. Because of this coherent response, electronic manipulation of the acoustooptic modulators drive signal can produce unique optical imaging effects, effects which cannot be achieved with the flying spot scanner architecture. An example of this electronic processing is a shift in the plane of best focus of the scanner which is achieved by passing the modulators drive signal through a chirp filter. This electronic focus shift can enable a three dimensional television display.

The Scophony Spatial Light Modulator

The Scophony scanner uses the same optical elements as the more familiar flying spot scanner: a rotating polygon mirror, an acoustooptic (A/0) modulator, and a laser light source. The flying spot scanner is designed to construct its image a pixel at a time; no more than one pixel is illuminated at any given instant. The Scophony scanner is designed to image a broad swath of the A/0 modulators acoustic pulses onto the photoreceptor. Many pixels are illuminated at any given instant in the Scophony scanner. The acoustic pulse image motion is frozen in place by a compensating scanning action. The result is a scanner with a coherent imaging response. This coherent response implies that the optical phase of a given pixel profoundly influences the formation of neighboring pixels. The optical phase at the scanner image plane is driven by the electronic phase of the video signal applied to the A/0 modulator. This coherent response enables electronic manipulation of the video drive signal to have significant impact on the optical imaging performance of the scanner. Two electronic manipulation schemes are proposed for doubling the resolution of the Scophony scanner, one scheme for analog video signals, and one scheme for binary digital video signals. Each scheme gives superior contrast ratio performance compared with the flying spot scanner.

VLSI-based image bar for laser beam recording

There are many image bar technologies which make use of a full width light modulator which projects one-to-one onto the photoconductor. An alternative to these full width image bars makes use of a micro image bar, in which all of the drive electronics are integrated on a single monolithic VLSI circuit. The TIR linear spatial light modulator is such a device which is built using an integrated circuit in conjunction with an electro-optic crystal to achieve light modulation.There are many image bar technologies which make use of a full width light modulator which projects one-to-one onto the photoconductor. An alternative to these full width image bars makes use of a micro image bar, in which all of the drive electronics are integrated on a single monolithic VLSI circuit. The TIR linear spatial light modulator is such a device which is built using an integrated circuit in conjunction with an electro-optic crystal to achieve light modulation.