High-speed and ultralow-chirp 11.55 μm multiquantum well λ/4-shifted DFB lasers

A high-speed ultralow-chirp 1.55 μm multiple-quantum-well (MQW) λ/4-shifted distributed feedback (DFB) laser is demonstrated by using low capacitance structure and by the optimization of an NQW structure in an active layer. A 3-dB bandwidth of 14 GHz as an NQW-DFB laser was achieved, and a chirp width of 3.4 Å (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 of NQW 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