Gain saturation is treated by formulating a model that accounts for the dependence of gain on irradiance level in distributed-feedback lasers. Solutions of the coupled-mode equations of the model are obtained numerically and are presented for both overcoupled and undercoupled laser structures (KL in the 10-13-10 range). Parasitic losses that are distributed uniformly within the structure are found to influence the output power characteristics of distributed-feedback lasers. Also the optimum coupling strength that results in the most efficient conversion of pump power to useful laser output is determined. The optimum coupling strength for any distributed-feedback laser is dependent on the magnitude of the parasitic losses and on the required output-power level.
K. O. Hill and A. Watanabe, "Envelope Gain Saturation in Distributed-Feedback Lasers," Appl. Opt. 14, 950-961 (1975)