Notch filtering using a multiple passband AOTF in the SWIR region.

A notch filtering operation was accomplished using a TeO₂ acousto-optic tunable filter (AOTF) with 16 simultaneous overlapping passbands in the shortwave infrared wavelength region. By switching off specific radio frequency signals applied to the AOTF, laser wavelengths corresponding to the inactive passbands are rejected, providing see-through capability with the remaining wavelengths. The rejection level was determined by leakage through the sidelobes of adjacent passbands, as was shown by theory and corresponding measurements. By switching off multiple passbands near the laser wavelength, the rejection level can be increased at the expense of reduced see-through capability. The AOTF imaging system used telecentric confocal optics that compensate for AOTF aberrations, which are severe at high sidelobe operation.