250kHz Linewidth Operation in Long Cavity 1.5µm Multiple Quantum Well DFB-LDs with Reduced Linewidth Enhancement Factor

Multiple quantum well distributed feedback laser diodes (MQW-DFB-LDs) are attractive as narrow linewidth light sources for coherent optical communications use. Although narrow spectral linewidth operations have been reported in long wavelength MQW-DFB-LDs[1], the design for further linewidth reduction has not been clarified yet. This paper reports that negative detuning as well as threshold carrier density reduction are extremely important for narrow linewidth operation. The narrowest ever achieved 250kHz spectral linewidth was obtained, based on the experimental characterization of linewidth enhancement factor a.