HIGH-SPEED AND ULTRALOW-CHIRP 1.55 MU-M MULTIQUANTUM WELL LAMBDA/4-SHIFTED DFB LASERS

A high-speed ultralow-chirp 1.55-mu-m MQW lambda/4-shifted DFB laser is demonstrated by employing low capacitance structure and by the optimization of an MQW structure in an active layer. A highest 3 dB bandwidth of 14 GHz as an MQW-DFB laser was achieved, and a record chirp width of 3.4 angstrom (20 dB down full width) was also achieved at 10 Gb/s direct modulation. In addition, kL dependence of chirp width is identified by the adiabatic chirping width is identified by the adiabatic chirping due to the spatial hole burning along a laser axis. From the systematic investigation of the nonlinear gain coefficient epsilon of MQW lasers as well as bulk lasers, it is suggested that the physical origin of nonlinear damping can be explained by the spectral hole burning theory.