Gain saturation in circular-grating distributed-feedback semiconductor lasers

We report numerical results for gain saturation in circular-grating distributed-feedback semiconductor lasers. Our model includes a radially varying nonlinear gain and a uniformly distributed grating loss in the solution of the coupled-mode equations. Our results show that lossy, high-power operation results in an optimum coupling strength for efficient conversion of pump power into useful output power. Our results also show a multimode spectrum for large-coupling strengths, a consequence of mode competition induced by a spatially varying gain distribution. Single-mode selection entails operating at approximately the optimum coupling coefficient determined for efficient pumping.