On the validity of estimating axial nonuniformity of photon density from output power ratio in uniform grating DFB lasers

The validity of the method of estimating nonuniformity in axial photon distribution from front-to-rear output power ratio has been studied by an effective index transfer matrix method. The correlation between the front-to-rear output power ratio and the maximum-to-minimum photon density ratio is shown to be good over the whole useful range of the grating coupling coefficient in uniform grating DFB laser with low-reflection/high-reflection facets, and an accurate estimation is possible. However, the correlation becomes poor as the reflectivity of the high-reflection facet decreases and the coupling coefficient increases, resulting in poor estimation.