GAIN NONLINEARITIES IN SEMICONDUCTOR-LASERS - THE COMBINED EFFECT OF THE MODULATION OF THE CARRIER DENSITY AND THE ELECTRON-TEMPERATURE AT THE BEAT FREQUENCY OF INTERACTING OPTICAL-FIELDS

The influence of the modulation of both the carrier density and the el ectron temperature by the beating of the fields of lasing and nonlasin g modes on the spectral behaviour of semiconductor lasers is analyzed. Analytic expressions for the nonlinear gain using two-mode and three- mode models are obtained. It is shown that the strong asymmetry in the nonlinear gain is introduced by the linewidth enhancement factor and by the factor which relates gain and refractive index changes caused b y the electron temperature changes and the slight asymmetry in the non linear gain for three-mode case is introduced by the dispersion of the group refractive index. It is found that the single-mode stability in semiconductor lasers is governed by these factors and by the dispersi on of the group refractive index.