Modeling of distributed feedback semiconductor lasers with axially-varying parameters

A numerical model that is capable of predicting important laser characteristics such as the threshold gain and the gain margin between the main and side modes for a distributed-feedback (DFB) semiconductor laser of arbitrary complexity is described. The method consists of solving the coupled-mode equations with axially varying parameters iteratively until the boundary conditions at the two facets are satisfied. The numerical model is applied to two DFB laser structures. In the case of a multiple-phase-shift DFB laser the results show that such devices can have a more uniform axial distribution than that of a conventional quarter-wave-shifted DFB laser while maintaining sufficient gain margin between the main and side modes. In the case of a dual-pitch DFB laser it is shown that the incorporation of a slightly different grating period ( approximately 0.1%) over a small section can provide a gain margin that is comparable to that achieved in quarter-wave-shifted DFB lasers.<>