Theoretical analysis of emission characteristics of second-order distributed feedback semiconductor lasers

Abstract

Based on the modified coupled-wave theory, the emission characteristics, including threshold gain, photon density distribution in the cavity, and external differential quantum efficiency for second-order DFB lasers are investigated. Numerical simulation results show that for given device structure with wavelength of 1.55 μm, the feedback coupling coefficient and the surface radiation coupling coefficient of the second-order grating have great influence on the emission characteristics of the device. By choosing different duty cycles of the grating, we can change the two coupling coefficients, which affect the emission characteristics. For an overall consideration, an optimal duty cycle of 0.43 is chosen. The optimized results show that the device works without degeneracy modes and spatial burning hole. Besides, the side-mode suppress ratio (SMSR) and external differential quantum efficiency reach as high as 42 dB and 47%, respectively. Show more