Liquid-crystal integrated silicon spatial light modulator

Diffraction based phase compensation method for phase-only liquid crystal on silicon devices in operation

A method to measure the optical response across the surface of a phase-only liquid crystal on silicon device using binary phase gratings is described together with a procedure to compensate its spatial optical phase variation. As a result, the residual power between zero and the minima of the first diffraction order for a binary grating can be reduced by more than 10 dB, from -15.98 dB to -26.29 dB. This phase compensation method is also shown to be useful in nonbinary cases. A reduction in the worst crosstalk by 5.32 dB can be achieved when quantized blazed gratings are used.

Polarimetric characterization of liquid-crystal-on-silicon panels

Mueller matrix imaging polarimetry of liquid-crystal-on-silicon (LCoS) panels provides detailed information useful for the diagnosis of LCoS problems and to understand the interaction of LCoS panels with other projector components. Data reduction methods are presented for the analysis of LCoS Mueller matrix images yielding contrast ratio, efficiency, spatial uniformity, and the calculation of optimum trim retarders. The effects of nonideal retardance, retardance orientation, and depolarization on LCoS system performance are described. The white-state and dark-state Mueller matrix images of an example LCoS panel are analyzed in terms of LCoS performance metrics typical for red-green-blue wavelengths of 470, 550, and 640 nm. Variations of retardance, retardance orientation, and depolarization are shown to have different effects on contrast ratio, efficiency, and brightness. Thus Mueller matrix images can diagnose LCoS problems in a way different from radiometric testing. The calculation of optimum trim retarders in the presence of spatial variations is discussed. The relationship of the LCoS retardance in single-pass (from front to back) to the double-pass retardance (from entrance to exit) is established and used to clarify coordinate system issues related to Mueller matrices for reflection devices.

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.

Reconfigurable array interconnection by photorefractive correlation

Electronic parallel processors might communicate more effectively by photons sent through glass or air than by electrons sent through wires, but quickly routing thousands of optical signals remains a problem. Previous photorefractive interconnection networks have dedicated one hologram to each input channel. Instead, we compute a control image from the entire network configuration and store it as a single color-keyedvolume hologram. This lets us use hologram superposition for fast switchingbetween multiple prestored patterns. During operation, data signals from the input modulator array, powered by a shared wavelength-tunable laser, are correlated optically with one color-matched connection hologram to produce the output array. This decouples both data rate and interconnect switching speeds from the slow photorefractive response. We can display arbitrary connection weights using simple binary-phase spatial light modulators and gracefully accommodate modulator limitations by trading off control-image bandwidth for output signal-to-noise ratio. Experimental results with color-multiplexed reflection holograms in z-cut LiNbO(3) confirmed our theoretical predictions that this approach works best for densely connected networks with high fan-in to each output. We obtained an average aggregate signal-to-noise ratio of more than 200:1 for 1024 inputs and outputs.

Monolithic integration of a silicon driver circuit onto a lead lanthanum zirconate titanate substrate for smart spatial light modulator fabrication

The monolithic integration of N-channel metal-oxide-semiconductor (NMOS) driver circuits in silicon thin films onto a lead lanthanum zirconate titanate (PLZT) substrate is reported. Two integration methods are compared. Both methods result in NMOS transistors that exhibit electrical properties that are close to those of transistors fabricated in bulk silicon. The characteristics of PLZT modulators driven by thin-film transistors are also similar to those of bulk PLZT modulators. These techniques promise new spatial light modulators of high complexity and performance that good-quality silicon and bulk PLZT can offer.

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.