ANALYSIS OF THE PHASE-AMPLITUDE COUPLING FACTOR AND SPECTRAL LINEWIDTH OF DISTRIBUTED FEEDBACK AND COMPOSITE-CAVITY SEMICONDUCTOR-LASERS

The method for the analysis of semiconductor lasers based on a Green's function approach is developed in a form suitable for complex-cavity structures. Besides the spontaneous emission rate, the effective phase-amplitude coupling factor can also be accurately evaluated. The application of this method to distributed feedback (DFB) and composite-cavity lasers gives interesting new results. For DFB lasers, the spontaneous emission rate is strongly dependent on both the facet reflectivities and the grating coupling coefficient. The effective phase-amplitude coupling factor depends on the wavelength detuning from the gain maximum. The calculated linewidth of DFB lasers differs considerably from previous results and gives a better agreement with reported experimental results. For composite-cavity lasers, the frequency dependence of the equivalent reflectivity has a strong impact on the phase-amplitude coupling factor and the spontaneous emission rate. Distributed Bragg reflector (DBR) lasers are investigated as an example of a composite-cavity structure. An optimum grating coupling coefficient in the Bragg region is found which minimizes the spectral linewidth. Negative detuning from the Bragg frequency results in low phase-amplitude coupling factor and narrow spectral linewidth. This method is also useful for lasers with multiple active sections. © 1990 IEEE