An analysis of the linewidth of DBR lasers

It is demonstrated that linewidths small compared to those of FP semiconductor lasers can be achieved by suitably designed DBR-lasers. A formerly used treatment is applied, developed for lasers with arbitrary external feedback. This treatment is applicable for the DBR lasers since the configuration can be looked at as a FP-laser with frequency dependent facet reflectivities. The treatment is not applicable to the DFB-laser where feedback is distributed over the active region.