Dependence of spectral linewidth of DFB lasers on facet reflectivity

We studied theoretically and experimentally the dependence of the spectral linewidth of DFB lasers on the facet reflectivity. It is shown theoretically that a higher facet reflectivity gives a narrower spectral linewidth, but gives a smaller yield of single-longitudinal-mode operation. We also show experimentally that the spectral linewidth takes its minimum value at a front facet reflectivity of about 5%.