Polarization characteristics of distributed feedback semiconductor lasers

The threshold behavior of an index-guided distributed feedback semiconductor laser is analyzed theoretically with particular attention paid to the effect of internal stress on the polarization of stimulated emission. Using parameters appropriate for a 1.55-μm InGaAsP laser, a distributed feedback laser is found to have a lower threshold margin between the transverse electric (TE) and transverse magnetic (TM) modes than a similar Fabry–Perot laser. This threshold margin is strongly dependent on the internal stress normal to the active layer and depending on its magnitude either TE or TM mode may reach threshold first. The present analysis is in qualitative agreement with the experimental observations and is useful for device optimization.