TUNABLE HOLOGRAPHIC FILTER

Electronically tunable optical filters are important components of freguency-agile sensor systems. Acousto-optic filters (AOTF) offer the best near-term technology for implementation of frequency-agile imaging optical sensors. These filters however, suffer from several limitations. On important deficiency is the limited off-band rejection attainable with these devices which is typically of the order of 10(-4) far off-band and closer to 10(-1) near off-band due to the presence of side lobes. This limited off-band rejection limits the application of AOTF-based devices to target discrimination problems where a weak signal must be discriminated against a high background. Recently, holographic filters have become available with extraordinarily high off-band rejection of the order of 10(-7). These devices, however, are fixed-bandpass devices, and are not suitable for frequency-agile imaging sensors. The present porposal is to develop an innovative electronically tunable optical filter with off-band rejection comparable to that of a holographic filter.