Abstract: Nonlinear optical techniques are utilized to provide an adaptive notch filter for removing narrowband noise from broadband RF communication signals. The received RF signal is converted to a corresponding acoustic wave propagated in an acousto-optic cell. Two mutually coherent beams of light are passed through and diffracted by the acousto-optic cell. The diffracted beams are modulated by the acoustic wave, the second beam being modulated at a predetermined time delay with respect to the first beam. By proper selection of the time delay, the narrowband components of the two beams remain mutually coherent while the broadband components become mutually incoherent. The two diffracted beams are then mixed within a photorefractive crystal so that a first mixed beam comprises substantially all of the narrowband components while a second mixed beam consists essentially of only the broadband components.