An optical signal processing system includes apparatus for identifying a complex signal by an optical matched filter. The matched filter consists of a hologram recorded by projecting coherent light through an acoustic delay line arranged to propagate an acoustic wave therein with multiple intersecting paths. This hologram is now used as the optical matched filter for identifying a signal which is impressed on the same acoustic delay line and projected on the hologram. The hologram may be so arranged as to focus the reference beam substantially in a point whenever the signal to be recorded matches the previously recorded signal.
HOLOGRAPHIC CORRELATOR WITH A FOLDED PATH ACOUSTIC CELL INPUT