A dynamic optical system for producing variable delays of a radio frequency signal is presented. The approach uses a micro-laser diode array to tap an acousto-optic (AO) cell at varying spatial positions along the acoustic channel to generate multiple delayed versions of the input signal to the AO cell. The diffracted and undiffracted laser light exiting the AO cell are heterodyne detected at a photodiode. The resulting output signal is maintained at the input signal frequency, but with a delay corresponding to the tap position along the AO delay line. The use of the laser diode array allows for a programmable time delay, programmable weighting of each delay, a large number of delays equal to the number of elements in the diode array, and multiple delays at one time. Experimental results are presented for a two-tap proof of concept system and a sixteen-tap programmable delay line. Results include dynamic range measurements of the input RF power and the input laser power for the system. Areas of application for this device include use as a programmable transversal filter for clutter cancellation in radar, false signal generation in electronic warfare, and coded waveform generation in communication systems.
Christopher W. Keefer,
"Compact and programmable delay line using a micro-laser array", Proc. SPIE 2240, Advances in Optical Information Processing VI, (29 June 1994); doi: 10.1117/12.179128; https://doi.org/10.1117/12.179128