Joint transform correlation using optically addressed chiral smectic liquid crystal spatial light modulators

Experimental results of joint transform correlators that utilize a high speed, binary or analog, optically addressed spatial light modulator (OASLM) in the Fourier plane are presented. The OASLMs consist of an amorphous silicon photosensor and a smectic A* or C* ferroelectric liquid crystal modulator. The OASLMs were used to compute the power spectra of the interfering Fourier transforms of the input and reference images. The devices are fabricated by depositing an a-Si:H photodiode in the PIN configuration on an indium-tin-oxide coated sheet of soda lime glass. A chiral smectic ferroelectric liquid is sandwiched between the a-Si:H thin film and another indium-tin-oxide coated sheet of glass. This produces a switchable halfwave plate at the read beam wavelength. For the smectic A* OASLM, heating elements are used to raise the temperature of the ferroelectric liquid crystal above the smectic C*—A* phase transition. The active area of the devices is a 1.27-cm diam circle. The devices exhibit response times of 10-155 µs with a resolution of 40 line pairs/mm.