Optical Comparator Based on an FLC over Silicon SLM

Abstract

Optics provides the potential medium to deal with information at‘the speed of light’, hence it is a logical progression from the current electronic state of the art. By exploiting the inherent parallelism of free-space optics, it is possible to design and build optical image processors capable of analysing thousands of two-dimensional images every second. By using ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as two dimensional light modulation devices, it is possible to build either a binary phase only matched filter (BPOMF)[1] or a joint transform correlator (JTC)[2]. Both architectures exploit the fact that FLCs can be used for binary phase modulation which is independent of both tilt angle and cell thickness and is capable of switching speeds in excess of 10μsec. A further advancement is the development of FLC over silicon VLSI SLMs[3,4], which allow the integration of circuitry with the FLC over mirrors to make an active backplane high speed binary phase modulator with very low pixel pitches. Hence, miniaturisation of the correlator is possible. In the case of the BPOMF, it is possible to make a very compact correlator[5], however it will always be limited by the optomechanical system used to make the correlator. This is not such a major issue with the JTC and can be completely eliminated by adopting the binary phase l/f JTC architecture[6].