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Optimization of grating structures in complex-coupled MQW DFB lasers with absorptive gratings

There is a trade-off between the low threshold gain and large fabrication tolerance. Among the grating structures studied, the double grating structure consisting of the absorptive grating on the index grating has the largest fabrication tolerance of the threshold gain and the coupling strength. The fabrication tolerance of coupling ratio is very large for all grating structures studied.