All-optical high gain transistor action using second-order nonlinearities

It is shown that the output stage of a phase-matched frequency doubler is highly sensitive to the phase and amplitude of a weak injected second harmonic signal. Such devices may be regarded as all-optical transistors with very high small signal gain, resulting in strong modulation of the pump light. Gains as high as 60 dB appear to be experimentally feasible in the recently reported highly efficient quasi-phase-matched frequency doublers formed by periodic domain inversion in LiNbO₃.