High-repetition-rate optical pulse generation and control techniques

In this paper, we report the generation of a high-repetition-rate optical pulse train with a mode-locked laser diode (MLLD) and its control techniques. We discuss key technologies to increase the mode-locking frequency and reveal that passive mode-locking based on an intracavity semiconductor saturable absorber is a promising way to achieve mode-locking at a very high repetition rate exceeding hundreds of GHz. Generation of a transform-limited 480 GHz optical pulse train was successfully achieved using a short-cavity (174 mum) MLLD. We also propose and demonstrate two novel techniques, subharmonic optical synchronous mode-locking and an all-optical down-converting method, to stabilize such an ultrafast MLLD and to evaluate the jitter characteristics accurately by all-optical methods without limitations imposed by an electronic device's speed. Stabilization of ultrafast MLLDs (160 and 480 GHz passive MLLDs) and the jitter measurements were successfully demonstrated.