Nonlinear gain in semiconductor ring lasers

Nonlinear gain in semiconductor ring lasers has been investigated theoretically based on density-matrix equations, including the effects of carrier density pulsations, carrier heating, spectral hole burning, and carrier diffusion. Expressions for nonlinear susceptibilities are derived analytically and compared with previous theoretical results. It is found that carrier diffusion have strong effects on both the amplitude and beat frequency dependency of the nonlinear susceptibilities. Various nonlinear parameters are also calculated based on the expressions obtained, and are consistent with published experimental results by other groups.