High-speed compact correlator using VLSI liquid-crystal spatial light modulators

Abstract

The design and operation of a high-speed compact correlator that uses 176 × 176 very-large-scale integration/ferroelectric liquid-crystal (VLSI/FLC) spatial light modulators is presented. The VLSI/FLC devices1 have pixels on 30 μm centers and are used as the input and filter planes of a Van der Lugt correlator. The small pixel size of the spatial light modulators and the folded optical design, which uses telephoto transform lenses, allow the system to be compacted to roughly a 10 cm cube, while maintaining proper scaling between the input and filter planes. The use of ferroelectric liquid-crystal materials, which can switch in less than 25 μs at room temperature, allows for potential system throughput speeds greater than 40000 correlations per second. However, operation at such high speeds is beyond the capacity of current correlation-plane detection methods. For correlation rates of 500-1000 Hz, three detection methods employing standard charge-coupled devices, custom VLSI, and grey-coded photodiodes are investigated.2 The influence of VLSI device parameters, such as resolution, speed, and contrast ratio, on correlator performance are modelled, and experimental results are presented.