Facet phases and sub-threshold spectra of DFB lasers: Spectral extraction,features, explanations, and verification

The sub-threshold spectra of distributed feedback (DFB) lasers are heavily influenced by the phase of the internal grating with respect to the end fac ets. In this paper, we document features commonly observed in sub-threshold spectra and explain these features as manifestations of the facet phases. We extract estimates of facet phases by fitting a probability-amplitude tra nsfer-matrix model to spectra from six truncated-well DFB lasers, and use t he probability-amplitude model to document, isolate, and explain the sub-th reshold spectral dependence on facet phase. To verify the accuracy of the a pproach that me have taken, we compare estimates of the facet phases from t he fits to independent measurements of the facet phases using a scanning ph otoluminescence method. The results from the two methods are compared and a re found to be in agreement. The agreement validates our use of the probabi lity-amplitude model in this paper to explain laser facet phase phenomena.