ANALYTIC THEORY OF COHERENT CROSS-GAIN MODULATION IN SEMICONDUCTOR TRAVELING-WAVE AMPLIFIERS

We report a simple analytic solution to the problem of cross amplitude -phase modulation in nonlinear two-wave mixing, under the approximatio n of constant saturating power. The results are applied to travelling- wave semiconductor laser amplifiers where the linewidth enhancement fa ctor inevitably leads to amplitude-phase coupling and asymmetric energ y transfer. Our solution is used to obtain the transmission gain of ea ch beam, the spectral profile and the amplifier input-output character istics. Limits are established as to the applicability of the analytic solution, by comparison with numerical solutions to the related full four-wave mixing problem.