Signal correlator with programmable variable time delay based on optical coherent transients

An optical coherent transient signal correlator with variable true time del ay is experimentally demonstrated. Storage of a pattern waveform in a spect ral-spatial population grating is achieved by interfering it with two chirp ed pulses instead of a single brief reference pulse. Correlative signal pro cessing results when a data waveform probes that grating, stimulating an em itted coherent output signal after the appropriate time delay. The signal i s the result of a six-wave mixing process that can be as efficient as the t raditional four-wave mixing process using a single brief reference pulse. F requency shifting of the two chirped pulses enables programming of a variab le time delay in the grating without changing the timing of the programming pulses. This concept is experimentally demonstrated with variable time del ays over 448 ns (offset by greater than 1 mu s) for the auto-correlation of a code with an experimentally limited bandwidth of 40 MHz. Processing band widths exceeding 10 GHz are achievable in materials such as Tm3+:YAG (0.1 a t%). (C) 2000 Elsevier Science B.V. All rights reserved.