Abstract

Photorefractive (PR) devices have found applications in optical computing, image processing and pattern recognition^[1–3], because PR materials provide unique features such as real time operation, optical gain, storage, nonlinear operations, phase conjugation and correlation. New PR materials are being investigated in order to meet the device and system requirements of sensitivity, speed, and operation wavelength (e.g., response to the near infrared spectral range for systems operated with semiconductor lasers). Compound semiconductors may satisfy these requirements. For example, optical signal amplification by two-beam coupling and amplified phase-conjugate beam reflection by four-wave mixing have been reported in GaAs^[4] and InP^[5] at the wavelength of 1.06 μm. Recently, GaP^[6–7] was shown to possess a relatively weak PR effect in the spectral range of 0.6 to 0.9 μm. In this manuscript we report enhancement of the PR effect in GaP using an externally applied electric field and moving grating. In particular, two- and four-wave mixing experiments were used to demonstrate a gain coefficient of Γ = 1.9 cm^–1 and a phase conjugate reflectivity, R= 4.5%. In addition, several figures of merit of GaP, i.e., steady-state index change, absorption coefficient, response time and PR sensitivity were characterized.

© 1991 Optical Society of America