Applied Electric Field Effect on Photorefractive GaAs,

Compound semiconductors such as gallium arsenides. are known to be very fast photorefractive materials. However, due to their relatively small electro-optic coefficient, their diffraction efficiency is much smaller than that of most oxide materials such as BaTiO3. Even so, easily detectable signal with fairly good signal to noise ratio can be usually achieved in a GaAs based application without -the aid of an external electric field due to the cross polarization coupling capability of GaAs and the high sensitivity of modern video cameras. For example, in a recently demonstrated real-time optical image correlator, the correlation output was normally strong enough to saturate the vidicon camera used. On the other hand, in some applications such as the ring oscillator, the double phase conjugate mirror, and the self-pumped phase conjugator, a sufficiently large net two-beam coupling gain is needed. In compound semiconductors, net gain had been achieved by applied electric field techniques.