Douglas J. McKnight

256 × 256 liquid-crystal-on-silicon spatial light modulator

A 256 × 256 pixel spatial light modulator (SLM) is designed and constructed by the use of liquid-crystalon-silicon technology. The device is a binary electrically addressed SLM with a measured zero-order contrast ratio of 70:1 and an imaged contrast ratio of 10:1. The pixel pitch is 21.6 µm, which gives an array size of 5.53 mm. The electronic load time is 43 µs, and the 10%-90% switching time of the liquid crystal is ~75-80 µs at room temperature, which implies a maximum frame rate of ~8.3 kHz. We discuss the design trade-offs that are intrinsic to this type of device and describe how the primary application for the device in an optical correlator influenced the final design.

Complex phase/amplitude spatial light modulator advances and use in a multispectral optical correlator

Optical processing systems often require compact high frame rate spatial light modulators (SLMs), usually with application specific modulation requirements in the complex plane. In this paper we discuss several advances at Boulder Nonlinear Systems toward this goal, including our liquid crystal (LC) on VLSI 128 X 128 analog SLM, and our multispectral hybrid incoherent to coherent converter.We also present the analysis of optical modulation possibilities when utilizing zero twist nematic and planar aligned chiral smectic LC on a reflective backplane. Finally we present the design of a multispectral optical correlator for machine vision applications such as food inspection, security, or manufacturing inspection.

Miniature liquid-crystal-on-silicon display assembly

A novel integrated assembly process for miniature liquid-crystal-on-silicon displays using photodefinable benzocyclobutene resin is presented. Spin coating speed defines the cell gap, photolithography defines the cell perimeter and spacers, and thermocompression bonding provides the adhesion. The photodefined adhesive spacers provide thin liquid-crystal cell gap control (<2.5 microm) with excellent uniformity (+/-100 nm) for glass-on-glass and glass-on-silicon assemblies. The resin is compatible with common liquid-crystal alignment films and exhibits a bonding shear strength of 22+/-3.2 MPa The assembly process flow and characterization of demonstration devices are described.

Packaging of a 128 by 128 liquid-crystal-on-silicon spatial light modulator using self-pulling soldering

A self-pulling soldering technology has been demonstrated for assembling liquid crystal on silicon (LCOS) spatial light modulators (SLMs). Solder joints with different profiles and sizes are designed to provide vertical surface tension forces to control the gap accommodating the ferroelectric liquid crystal (FLC) layer in the range of a micron with sub-micron uniformity. This technology provides an automatic, batch assembly process for a LCOS SLM through one reflow process. The component designs and process optimization are described, and the first operational results are presented.<<ETX>>

ELECTRICALLY ADDRESSED 256 BY 256 LIQUID-CRYSTAL-ON-SILICON SPATIAL LIGHT MODULATOR

A 256 by 256 pixel spatial light modulator has been designed and constructed with liquid-crystal-on-silicon technology. The device is a binary electrically addressed spatial light modulator with a measured zero-order contrast ratio of 70:1 and an imaged contrast ratio of 10:1. The electronic load time is 43 μs, and the 10-to-90% switching time of the liquid crystal is 50 μs (turn-on) and 50 μs (turn-off), giving a maximum frame rate of ∼10 kHz. Its design for a specific application is described, and the first operational results are presented.

A HOLOGRAPHICALLY ROUTED OPTICAL CROSSBAR USING A FERROELECTRIC LIQUID-CRYSTAL OVER SILICON SPATIAL LIGHT MODULATOR

Abstract Ferroelectric liquid crystal spatial light modulators can be used to display high quality binary phase holograms, and incorporated into programmable free space interconnects. These are potentially highly efficient, and have advantages over conventional shutter based architectures. Such structures have applications in telecommunications and optical processing. In this paper a 16 channel ‘crossbar’ interconnect is presented. Hologram measurement indicates the crossbar will function with a high noise margin. Device nonuniformities cause distortion in the hologram replay and techniques to compensate for this are discussed. Optical throughput and DC balancing of the liquid crystal currently restrict the performance of the switch: Possible solutions to these problems are detailed.

128 x 128 analog liquid crystal spatial light modulator

An analog 128 X 128 spatial light modulator (SLM) has been designed and constructed using liquid crystal on silicon technology. This device is loaded with eight-bit grey-level data in 100 microsecond(s) . Its pixel pitch is 40 micrometers giving an array size of 5.12 X 5.12 mm. Low-voltage ferroelectric liquid crystals are used for the electro-optic modulator. These analog materials have 50 microsecond(s) to 100 microsecond(s) switching times, implying a frame rate of approximately 5 kHz. This paper presents results of the analog SLM and discusses modulation enhancements for improving correlator performance.

Analog distorted helix ferroelectric liquid-crystal-on-silicon spatial light modulator

We report what are to our knowledge the first results from a liquid-crystal-on-silicon spatial light modulator that uses the distorted helix ferroelectric mode to perform analog light modulation. The spatial light modulator is an electronically addressed analog 128 x 128 pixel device with which we have demonstrated 16 gray levels and contrast ratios of 33:1 in the zeroth diffracted order and 6:1 when imaged. The liquid-crystal switching speed in this device is approximately 235 micros, which when added to the data load time of 100 micros gives a maximum frame rate of approximately 3 kHz.

High-speed liquid-crystal-on-silicon spatial light modulators using high-voltage circuitry

Two high-speed liquid-crystal-on-silicon spatial light modulators that use high-voltage circuitry are described. The high-voltage circuits used can provide 30 and 15 V for switching chiral smectic liquid-crystal spatial light modulators with 10-90% switching times of 30 and 50 micros, respectively. The ON/OFF contrast ratios are 13:1 and 15:1.

Continuous view of dc-balanced images on a ferroelectric liquid-crystal spatial light modulator.

A scheme is presented that permits a continuous view of an image displayed on a dc-balanced ferroelectric liquid-crystal-on-silicon spatial light modulator. I develop the theory and present experimental results, using a 256 x 256 ferroelectric liquid-crystal-on-silicon spatial light modulator. It is shown that both halves of the dc-balanced cycle can be made to produce identical outputs even when the illumination is polychromatic and the spatial light modulator liquid-crystal layer thickness is not an ideal half-wave plate and for an arbitrary liquid-crystal switching angle.