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-laye r multiquantum-well active grating for a mixed index and gain coupling have been fabricated and studied. The lasers exhibit distinct longitu dinal-mode behavior due to gain-coupling effects, including a high sin gle-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 ca vity lasers with the present structure have higher kappa(gain)L/kappa( index)L ratios and wider Fabry-Perot mode spacing than the longer cavi ty ones; these features enable the shorter cavity lasers to have a hig h single-mode yield (90%) and a high side-mode suppression ratio (55 d B). It is also confirmed that the facet reflectivity does not signific antly change the longitudinal-mode characteristics of the lasers. Expe rimental spectra have been successfully reproduced in the simulation a nd interpreted according to below-threshold analysis results.