Effect of residual facet reflectivity on the front-rear correlation and nonlinearity of L-I characteristics in quarter-wavelength-shifted DFB lasers

Combined effects of residual facet reflection and spatial hole-burning on the front-rear correlation and nonlinearity in L-I characteristics of quarter-wavelength-shifted DFB lasers have been studied by using an effective index transfer matrix method and rate equations. Changes in front-to-rear power ratio, caused by the spatial hole-burning and asymmetric facet-reflection due to the different grating end phases at the two facets, are shown to be responsible for both the correlation and the linearity problems, while the threshold gain change causes the linearity problem only. The problems are serious even in the cases of low facet reflectivity of 0.3%.