Threshold analysis of a chirped-grating distributed-feedback laser with the power series method

A new and efficient method for analyzing a chirped-grating distributed-feedback (DFB) laser is presented. We show that coupled-wave equations can be solved by use of the power series method. The single-mode gain margin of a linearly chirped-grating DFB laser is calculated for different chirping factors and coupling constants. We found that clearly optimum chirping exists for which the single-mode gain margin is maximum. The gain margins were also calculated for different positions of the cavity center. The effect of facet reflectivities and their phases on the gain margin was investigated. We found that the gain margin is maximum and the spatial hole burning is minimum for the cavity center at the middle of the laser cavity. (C) 1999 Optical Society of America OCIS codes: 140.3490, 140.3580, 230.6080, 270.3430.