APPLICATIONS LOOK AT THE USE OF LIQUID-CRYSTAL WRITABLE GRATINGS FOR STEERING PASSIVE RADIATION

Liquid crystal writable grating technology is being developed for beam steering in laser radar systems. We consider the ability of writable gratings to steer broad-spectral-band radiation for use in passive sensors. We find that there is potential for these devices in microscan systems because there is little or no dispersion for the small scan angles required in microscanning. The dispersion that is present is less than the resolution of the sensor considered here. For large angle steering we find that dispersion correction or a narrowing of the spectral bandwidth is required. The degradation in sensitivity resulting from narrowing the spectral bandwidth is considered. We find that a high-quantum-efficiency step-stare sensor with a two-dimensional focal plane array responsive over a narrow spectral width can achieve the same sensitivity as current linear scanning sensors while being able to steer the field of view (FOV) over a larger field of regard with no moving parts. Approaches for dispersion correction and postdetection correction are discussed. A promising approach for steering a narrow FOV with broad spectral content and good resolution is described.