LONG-CAVITY MULTIPLE-PHASE-SHIFT DISTRIBUTED FEEDBACK LASER DIODE FOR LINEWIDTH NARROWING

We developed a long-cavity multiple-phase-shift distributed feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing. We analyzed the threshold gain difference and the field uniformity along the laser cavity of the MPS-DFB laser by varying the amount and the position of phase shifts using the coupled-wave theory. It is shown that a large threshold gain difference and a uniform field distribution are obtained in the MPS-DFB laser with some special amount and position of phase shifts. Based on our analysis, we fabricated a MPS-DFB laser with a 1200-µm-long cavity and three phase shifts at 0.8 π, -0.8 π, and 0.8 π. This MPS-DFB laser exhibited stable single-mode operation, and showed a very narrow linewidth of 830 kHz at an optical output power of 25 mW. © 1990 IEEE