STABILITY IN SINGLE LONGITUDINAL MODE-OPERATION IN GAINASP-INP PHASE-ADJUSTED DFB LASERS

A single longitudinal mode (SLM) operating condition for phase-adjusted distributed-feedback (PA-DFB) lasers has been demonstrated both experimentally and theoretically. As expected, a high SLM operation yield of 80% was achieved in a moderately coupled case, up to a light output power of 10 mW. However, in strongly coupled cases, the two-mode operation with the TE 0 mode and the TE plus 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, the authors developed a theory that takes the spatial hole burning along the laser axis into account in explaining the longitudinal mode behavior. From the theory, moderate coupling (kL equals 1. 25) was found to be optimum to maintain the large threshold gain difference above threshold.