Non-Hermitian mode locking in an L-band monolithic InP dual-ring laser
Coupling between laser cavities provides a means of controlling optical modes through their gain, loss, and hybridization. Here we demonstrate electrically controlled mode locking in a monolithic InP dual ring laser operating in the L band without a dedicated saturable absorber. Independent biasing of the two rings accesses single mode emission, mode locking, and hybridized supermode operation, with a measured intermode beat frequency of 542 MHz in the latter regime. The laser generates 7.9 ps pulses at 18.11 GHz. A coupled cavity model describes how differential nonlinear detuning modifies the modal gain loss contrast, and time domain simulations yield pulse durations and spectral widths close to those measured experimentally. In a device incorporating saturable absorbers, reverse bias enables 3.1 ps pulses and reduces the integrated timing jitter from 9.06 to 2.46 ps relative to the unbiased condition. These results connect electrical control of coupled-cavity states with picosecond pulse generation in a monolithic InP semiconductor platform for high repetition rate optical communications and microwave photonics.