Monolithically Integrated Semiconductor Mode‐Locked Laser With Intracavity Pulse Picker for Dual‐Regime Low‐Repetition‐Rate Operation

ABSTRACT

A monolithically integrated quantum‐well semiconductor mode‐locked laser (SMLL) is presented, incorporating an intracavity pulse picker (PP) between the gain and saturable absorber (SA) sections to realize low‐repetition‐rate pulse generation with two distinct operating regimes. It can selectively output ultrashort pulses at subharmonic rates or operate in a seed‐pulse regime to achieve continuous and arbitrary repetition rate tuning: (i) under a shallow reverse bias on both SA and PP, the device extracts ultrashort pulses (5.37–7.68 ps) from a stable mode‐locked train to produce tunable subharmonic (1/N) repetition rates (5.1 MHz–1.02 GHz); (ii) under a deep reverse bias on both SA and PP, intracavity resonance is suppressed, enabling a continuous arbitrary repetition rate pulsed output tuning from 5 MHz to 3.4 GHz. The pulse widths range from 58 to 103 ps, achieving an ultra‐low duty cycle of 1/1942 at 5 MHz—the lowest repetition rate reported to date for monolithically integrated SMLL. Furthermore, this laser allows direct observation of pulse evolution from a single‐round‐trip seed to a stable mode‐locked state, providing an experimental approach for investigating the fundamental dynamics of the mode‐locking process.