Analysis of a dephased complex-coupled distributed-feedback laser by the power-series method

A novel power-series method to solve the couple-wave equations is introduced. The method is used to calculate the threshold gain margins of a complex-coupled distributed-feedback laser as functions of the ratio of gain coupling to index coupling (\kappa(g)\/\kappa(n)\) and of the phase difference between the index and the gain gratings. For coupling coefficient \kappa\iota < 0.9 the laser shows a diode degeneracy at specific values of the ratio \kappa(g)\/\kappa(n)\ cleaved facets. At phase differences pi/2 and 3 pi/2 between the gain and the index gratings, an antireflection coated complex-coupled laser becomes multimode, and a different mode starts to lase. The effect of facet reflectivity (both magnitude and phase) on the gain margin of a complex-coupled DFB laser is also investigated. Although the gain margin varies slowly with the magnitude of the facet's reflectivity, it shows large variations as a function of the phase, Spatial hole burning was found to be minimum at phase difference n/pi, n = 0, 1..., and maximum at phase differences pi/2 and 3 pi/2. (C) 2000 Optical Society of America.