Yield and device characteristics of DFB lasers: statistics and novel coating design in theory and experiment

Uncoated 1.55- mu m InGaAsP distributed-feedback (DFB) lasers show superior properties e.g. smaller linewidth and lower feedback sensitivity, in comparison to devices with low reflective facet(s). However, the phases of both front and rear mirror reflectivities, with respect to the grating, must be within sharp tolerances to get a stable dynamic single longitudinal mode device. These sharp tolerances lead to rather poor yield figures. A type of coating that allows the change of effective mirror phase by an arbitrary angle while preserving the superior high facet reflectivity is presented. To know what coating is optimum when applied to the batchwise process, a thorough statistical investigation in lasing behavior as a function of random facet phases, kL product, and front facet reflectivity is needed. Theoretical predictions of these quantities are presented, and also more general validity. The predictions on optimum phase rotation and the influence of absolute reflectivity values are verified experimentally and are found to very accurate.<
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