Long-cavity multiple-phase-shift distributed feedback laser diode for linewidth narrowing

A long-cavity multiple-phase-shift distributed-feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing is discussed. The threshold gain difference and the field uniformity along the laser cavity of the MPS-DFB laser are analyzed 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 the analysis, a MPS-DFB laser with a 1200- mu m-long cavity and three phase shifts was fabricated. This MPS-DFB laser exhibits stable single-mode operation and shows a very narrow linewidth of 830 kHz at an optical output power of 25 mW.<
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