DETECTING MODE HOPPING IN SEMICONDUCTOR-LASERS BY MONITORING INTENSITY NOISE

Mode-hopping semiconductor lasers exhibit intensity fluctuations which are correlated to the level of mode-hopping activity. It is shown tha t these fluctations occur at a level that is easily measured. A plot o f these fluctuations versus laser case temperature and injection curre nt displays periodicities in the conditions under which mode hopping o ccurs. We explain these regularities in terms of the peak gain wavelen gth passing the longitudinal mode wavelength as temperature changes. W e use the fact that the laser's junction temperature depends on both t he case temperature and on the injection current. We note that the ons et of mode hopping also depends on the transition from multimode to si ngle-mode operation. Implications for control of mode hopping are disc ussed.