PARTLY GAIN-COUPLED 1.55-MU-M STRAINED-LAYER MULTI-QUANTUM-WELL DFB LASERS

1.55 mum gain-coupled InGaAsP-InP DFB lasers which use a strained-layer multiquantum-well active grating for a mixed index and gain coupling have been fabricated and studied. The lasers exhibit distinct longitudinal-mode behavior due to gain-coupling effects, including a high single-mode yield. Cavity length dependence of the mode behavior has been experimentally studied and simulated using a transfer-matrix method. Both experimental and theoretical results indicate that the shorter cavity lasers with the present structure have higher kappa(gain)L/kappa(index)L ratios and wider Fabry-Perot mode spacing than the longer cavity ones; these features enable the shorter cavity lasers to have a high single-mode yield (90%) and a high side-mode suppression ratio (55 dB). It is also confirmed that the facet reflectivity does not significantly change the longitudinal-mode characteristics of the lasers. Experimental spectra have been successfully reproduced in the simulation and interpreted according to below-threshold analysis results.