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

Fast and low loss flexoelectro-optic liquid crystal phase modulator with a chiral nematic reflector

In this paper, we demonstrate a flexoelectro-optic liquid crystal phase-only device that uses a chiral nematic reflector to achieve full 2π phase modulation. This configuration is found to be very tolerant to imperfections in the chiral nematic reflector provided that the flexoelectro-optic LC layer fulfils the half-wave condition. Encouragingly, the modulation in the phase, which operates at kHz frame rates, is also accompanied by low amplitude modulation. The configuration demonstrated herein is particularly promising for the development of next-generation liquid crystal on silicon spatial light modulators.

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.

Optically produced true-time delays for phased antenna arrays

A device is described for generating true-time delays optically for microwave signals used in beam steering and beam shaping in phased-array antennas. The device can be adapted to provide delays from picoseconds to nanoseconds. A single, compact unit should provide parallel delays for more than 64 independent antenna elements with a greater than 6-bit resolution. The time delays are produced by multiple reflections in a mirror configuration with continuous refocusing. A single spatial light modulator selects independent optical path lengths for each of the parallel antenna elements. Amplitude control for beam shaping can be integrated into the device. The unit can be made rugged for harsh environments by use of solid-block construction. The operation of the true-time delay device is described, along with the overall system configuration. Preliminary experimental data are given.

Single-mode fiber optical crossbar routing switch with ferroelectric liquid-crystal-VLSI technology and free-space optics

We investigate a possible extension of the optically connected parallel machine crossbar system to telecommunication routing-switching systems. The critical issue concerns the realization of a free-space interconnection system between two single-mode fiber arrays in the case of a fully interconnected architecture, such as a crossbar system. In particular, we assess the throughput capability of such a system. This evaluation is based on both theoretical analysis and experimental results. We demonstrate that the number of channels is severely constrained by the limited numerical aperture of a single-mode fiber. Finally, we discuss some architectural alternatives and propose some technical recommendations for interconnecting single-mode fiber arrays in free space.