Mode selection in complex-coupled semiconductorDFB lasers

Mode suppression in complex-coupled DFB lasers with both in-phase and antiphase gain gratings is examined through a novel use of power balance. The theory is then backed up by more detailed arguments using a dynamic time domain model. The phase of the gain grating in relation to the index grating determines which mode of the DFB is suppressed. Longitudinal variations in the gain coupling coefficient caused by spatial hole burning provide additional side-mode suppression mechanisms.