Partly gain-coupled 1.55 μm strained-layer multiquantum-well DFB lasers

1.55-μm gain-coupled InGaAsP-InP distributed feedback (DFB) lasers which use a strained-layer multi-quantum-well (MQW) active grating for a mixed index and gain coupling have been fabricated and studied. The lasers exhibit distinct longitudinal-mode behaviour 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 κ_gainL/κ _inde 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)