Relaxation oscillations in quasi-single-mode semiconductor lasers

The intensity-relaxation-oscillation (RO) and damping rates, and the laser linewidth are measured and analyzed for a semiconductor laser under quasi-single-mode conditions. The RO frequency and the laser-linewidth dependence on laser power are measured, and are described well by the Henry single-mode theory. The relaxation-oscillation damping rate, however, shows a significant deviation from the expected power dependence, and is found to depend on the effective number of idle modes, and the fraction of energy in such modes. The observation is explained very well by a generalized quasi-single-mode theory that accounts for the collective contribution of the idle modes