David G. Vass

Evolutionary development of advanced liquid crystal spatial light modulators

Taking into account recent developments and present trends in devices and component technologies, the future development of electrically addressed liquid crystal spatial light modulators is considered. In particular, the combination of single-crystal-silicon active backplane and chiral smectic C liquid crystal technologies is shown to be promising. The ultimate limitations of such technologies for producing faster devices of higher complexity and functionality are assessed, and an advanced device, presently under development, is described.

Development of a spatial light modulator: a randomly addressed liquid-crystal-over-nMOS array

The construction of a 50- x 50-pixel spatial light modulator based on an active silicon backplane and using the hybrid field effect in nematic liquid crystals as the light modulating process is described. The design and electrical evaluation of the pixel array, which is fabricated in 1.5-microm nMOS and has an individual memory cell within each pixel, are discussed. The performances of a 16 x 16 prototype SLM and the new 50- x 50-pixel device are compared to provide an indication of progress toward high performance spatial light modulators with onboard pixel memory.

Improving the performance of liquid-crystal-over-silicon spatial light modulators:issues and achievements

The performance of liquid-crystal-over-silicon spatial light modulators has advanced rapidly in recent years. Most progress has centered around new device designs with increased bandwidth. In this paper we report on a number of techniques to improve the optical quality; these have applications in both current and future devices.

Mirror quality and efficiency improvements of reflective spatial light modulators by the use of dielectric coatings and chemical-mechanical polishing

To date, silicon backplane spatial light modulators have been characterized by poor-quality mirrors. Hillock formation during metal sintering has been identified as the source of this problem. Here hillock elimination is achieved by constraining the metal with a low-temperature plasma-enhanced chemicalvapor deposition silicon dioxide coating. A double-layer metallization procedure increases the silicon area available for circuitry and improves the mirror fill factor. Second-layer metal mirrors require a flat, intermediate dielectric substrate. Chemical-mechanical polishing is demonstrated to provide the flatness necessary to achieve high optical quality.

A 256 × 256 SRAM-XOR pixel ferroelectric liquid crystal over silicon spatial light modulator

Abstract An electronically addressed spatial light modulator is introduced. It is based on the hybrid technology of ferroelectric liquid crystal over silicon, and comprises an array of 256 × 256 pixels operating at a charge balanced frame rate of up to 2.1 kHz. The pixel circuit, incorporating a static random access memory latch and an exclusive-OR gate, has significant performance advantages over the single transistor design used elsewhere. The silicon backplane has also been used to help develop post-processing planarisation techniques for high fill-factor (84%), optically flat electrode mirrors.

High-performance spatial light modulator

The development of a ferroelectric liquid-crystal-over-single-crystal-silicon spatial light modulator is described. The reflective SLM has an array of 176 X 176 pixels over a clear aperture of 5.28 mm X 5.28 mm. Prototype devices driven from a specially designed high speed frame store have been operated at frame rates of approximately equals 1 kHz.

Real-time binary phase holograms on a reflective ferroelectric liquid-crystal spatial light modulator

A ferroelectric liquid-crystal spatial light modulator with an active silicon backplane is used to implement reconfigurable reflective phase holograms. Optical results are presented for an optimized computergenerated Fourier hologram.

The charge collection process in semiconductor radiation detectors

Abstract The discrepancy between the results of the calculation of the current pulse shape from a semiconductor radiation detector employing Ramos theorem and that based on the energy balance equation of the charge collection process is discussed. The conclusion is reached that the application of Ramos theorem is not valid in this case. A more general approach taking account of the change of electrostatic energy in the detector which is neglected in the energy balance equation, is suggested.

The scintillation process in gas proportional scintillation detectors with uniform electric fields

Abstract A model is developed to describe the formation of the secondary scintillation in a gas proportional scintillation detector having a uniform electric field. A simple expression is obtained for the instantaneous rate of emission of photons from the scintallator, assuming that the dominant excitation process in the gas is excitation by electron impact. The results of an experimental investigation of the photon emission from xenon following ionization of the gas by α-particles are presented. Our observations at various gas pressures and electric intensities are shown, with the aid of the model, to be consistent with those which have been obtained by other workers using parallel plate gas proportional scintillation detectors of significantly different design and mode of operation and exposed to X-rays as well as α-particles.

Measurements on ferroelectric liquid-crystal spatial light modulators: contrast ratio and speed

The contrast ratio and the speed of a 16 × 16 electrically addressed spatial light modulator, composed of a ferroelectric liquid-crystal layer on top of a VLSI silicon backplane, are measured with different methods but consistent results. The results are presented and compared with recently reported results on a similar spatial light modulator [Appl. Opt. 33, 2775 (1994)].