40 GHz passively mode-locked semiconductor lasers with a novel structure

We have presented a mode-locked semiconductor laser that operates at a 40 GHz repetition rate and in a 1.55 μm band. The mode-locked pulses have a nearly transform-limited time-bandwidth product of 0.38. The phase differences between oscillating modes were calculated and the results account for the transform-limited pulse generation. The reduction of phase difference was achieved by replacing a part of the gain region by passive waveguides in the cavity. The understanding and realization of such mode-locking operations will help us to make stable mode-locking semiconductor lasers that are applicable in long-haul optical communication systems.