J. Gourlay

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.

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.

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.

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)].

Time-multiplexed optical Hadamard image transforms with ferroelectric-liquid-crystal-over-silicon spatial light modulators.

The Hadamard transform is an example of a matrix transform that allows images to be represented in terms of orthogonal basis functions with binary-valued matrix elements. Such basis functions can be displayed on binary amplitude modulating ferroelectric-liquid-crystal-over-silicon spatial light modulators, permitting novel, real-time, and high-speed implementation of the transform on incoherently illuminated input scenes. An example of an optical Hadamard transform performed in real time by using a spatial light modulator is described. To show the validity of this optical decomposition, we electronically reconstruct the transformation data for comparison with the original input scene.

A comparative investigation into planarized liquid crystal over silicon spatial light modulators

Abstract Spatial light modulators (SLMs) are arguably the critical elements in coherent optical processing systems. Planarization techniques have been identified as crucial to increasing the performance of ferroelectric liquid crystal over very large scale integration SLMs when used in such systems. Planarization techniques allow enlarged and phase-flat pixel mirrors and improved liquid crystal alignment. This type of SLM is electrically addressed, i.e. transfers electrically represented information into an optical representation via binary phase modulation of the liquid crystal layer by the enlarged pixel modulation mirrors. The backplane design available for use in the study was a 176 × 176 pixel array dynamic random access memory. Investigations show an improvement in the device performance due to the planarization. This improvement was particularly evident when the SLMs were studied operating in a coherent optical system, where the diffraction efficiency was increased. The results compare favourably w...

Light-emitting polymer on CMOS: a new photonic technology?

A new hybrid optoelectronic technology has been developed which utilizes a very thin layer of light emitting polymer material on a CMOS silicon active-matrix substrate to create a 2-D array of independently programmable optical emitters. The technology has been developed thus far primarily for its use as a microdisplay. Here we detail aspects of device design and characterization. We consider the relevance of the new technology to optical and photonic systems other than displays.

Fabrication issues for silicon backplane active matrix miniature liquid crystal display

We describe a new technology which is appropriate for the production of lightweight, highly compact displays. It is based upon a thin layer of ferroelectric liquid crystal (FLC) on top of, and directly driven by, an active matrix backplane fabricated on single crystal silicon. While devices can be produced using fairly standard techniques, we have developed custon fabrication and packaging techniques, required for optimization of optical quality and performance. We have successfully developed the technology for spatial light modulators for use in applications such as optical correlators and programmable holograms. The FLC is configured in the binary surface stabilized configuration: the CMOS circuits are digital in nature. The device operates in reflection with each pixel having an aluminium pad which acts as a mirror to reflect light and as an electorde to control the state of the overlying FLC. The technology also shows promise as a display technology so we have demonstrated the devices as displays capable of displaying both grey scale and color. We have built FLC devices upon commercially fabricated wafers but have found it advantageous to carry out custom post processing order to improve performance. The main thrust to date has been the use of ECR oxide deposition followed by chemical mechanical polishing to provide an optically flat substrate for mirror deposition. This allows the deposition of flat mirrors which fill almost all of the pixel area; it also allows optimization of the mirror deposition for high optical quality and good FLC alignment. Work is also well advanced on a technique to fill the vias connecting to the mirror layer and on packaging devices to reduce bowing of the silicon and increase the thickness uniformity of the FLC layer. Recent results are demonstrated on LCDs fabricated above two silicon backplanes containing 176 X 176 pixels and 256 X 256 pixels respectively, the former having dynamic signal storage at each pixel, the latter static storage.

Scanning probe microscope study of obliquely evaporated SiOx and its indium-tin-oxide underlayer for the alignment of ferroelectric liquid crystals

Atomic Force Microscope images of obliquely evaporated SiOx onto indium-tin-oxide (ITO) thin film electrodes as used in liquid crystal displays show no pronounced regular structure of the SiOx thin films as used in theoretical approaches to explain the alignment of liquid crystals. Subsequent investigation of the morphology of the ITO surface using scanning tunneling microscopy shows that this surface is rough on many scales and shows step heights as large as 0.1 micrometers . Based on these observations we suggest two mechanisms which might be responsible for the liquid crystal alignment and methods for improving alignment.

Study of indium-tin-oxide surface morphology and its influence on obliquely evaporated SiOx alignment layers for ferroelectric liquid crystals

Abstract One of the various techniques used to align ferroelectric liquid crystals is the oblique evaporation of SiOx onto indium-tin-oxide (ITO) coated glass substrates. Starting from ideal (ie very flat) substrates computer simulations and experimental observations suggest that depending mainly on the angle of incidence of the SiOx flux onto the substrate, the SiOx film morphology changes from a columnar structure at near grazing incidence to a ‘ploughed field’ morphology at intermediate. In practice, however, the SiOx is deposited onto a highly textured ITO film. We used scanning tunneling microscopy (STM) to characterize the ITO surface of commercially available and in-house post-processed ITO coated glass substrates. An initial atomic force microscopy study of the deposited SiOx film shows that the usual growth pattern are impeded and even at intermediate deposition angles columnar growth is found.