Dependence of nonlinear gain effect on threshold gain in semiconductor lasers-an optimization for high-speed modulation

The dependence of nonlinear gain parameter and K factor on material gain in semiconductor lasers has been investigated theoretically by calculating (dg/dS)/sub s=0/, derivative of gain g with respect to photon density S. If spectral hole burning is assumed, the square of the line-shape function appears in dg/dS. This implies that the contributions from high-energy electron-hole pairs are reduced, and that (dg/dS)/sub S=0/ takes a finite negative value at transparent point (g=0). The nonlinear gain parameter, therefore, diverges, as the gain approaches zero. The K factor is minimized at a value of material gain, which is estimated to be 4.3 ps/sup -1/ for typical InGaAs/InGaAsP quantum well lasers. The confinement factor should be designed to maintain the gain at the optimum value.<>