An acousto-optic tapped delay-line finite-impulse-response filter that operates at a system intermediate frequency without requiring a reference optical beam is introduced. Principles of operation are theoretically derived and used to model the system frequency response and multiple-tap cross-talk performance. As an element of this derivation, a focused optical illumination of a diverging acoustic wave is analyzed. Experimental results are also provided for a multichannel acousto-optic tapped delay line operational over a 10-MHz bandwidth at an 80-MHz intermediate frequency.

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Hardware implementation of the steepest descent algorithm, as applied to multichannel adaptive jamming cancellation, requires the realtime correlation of wide bandwidth signals from multiple input channels. The described optical system uses a single-channel acousto-optic (AO) deflector as an input device for the adapted main antenna signal, where multiple jamming sources mask the target return, and a multichannel AO deflector as the input device for an array of auxiliary antennas, each receiving jamming energy. A time-integrating correlation between the main and auxiliary channels is calculated optically and produces an update to each weight function (stored in computer memory) in accordance with a steepest descent algorithm. The updated weight functions are optically reconstructed and used to tap a multichannel AO delay line, which carries the information from the array of auxiliary channels. A spatial sum of the output from the weighted delay line yields an estimate to the noise in the main channel. The multichannel optical time-integrating correlator has demonstrated realtime parallel computation of the correlation between two wide bandwidth auxiliary channels and the adapted main channel.

A novel optical architecture is presented that is based on the Hartley transform implementation of the classical adaptive least mean square (LMS) algorithm. The Hartley transform is employed to transform the time-domain signal of interest into the frequency domain, where filtering is performed via multiplication by the adaptively controlled filter transfer function. The inverse Hartley transform is then applied to this product resulting in the desired signal estimate, which is then subtracted from the desired signal to obtain the error to be used to upthte the filter transfer function. In addition to the presentation of this algorithm and the optical implementation, performance assessments based on the number of calculations required for the digital and optical approaches are provided.

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