Repetition-frequency tuning of monolithic passively mode-locked semiconductor lasers with integrated extended cavities

Repetition-frequency tuning characteristics of passively mode-locked laser diodes (LDs) were investigated in detail. Anomalous tuning characteristics were observed when the bias conditions of the LDs were changed. Theoretical analysis using conventional self-consistent mode-locking theory showed that the anomaly originated from the change of the detuning from the cavity's round-trip frequency due to gain/absorption saturation effects in the passively mode-locked lasers. A wide tuning range of 280 MHz (1.6% of the repetition frequency) was obtained by changing the bias conditions of the extended cavity.