Experimental demonstration of synchronization between two quantum dot passively mode-locked laser frequency combs utilizing bidirectional optical coupling

Abstract

Two monolithic edge-emitting passively mode-locked InAs/InGaAs semiconductor quantum dot lasers generating ps optical pulses at repetition rates of 10 GHz and optical frequency combs centered at 1260 nm are mutually coupled in an all-optical passive synchronization experiment. The two lasers, with different free-running repetition rates, are coupled through a long delay fiber path, they synchronize, and generate optical pulse trains with identical repetition rates in a wide range of experimental conditions (optical frequency, optical delay, and coupling strength). The common repetition rate can be easily fine-tuned with the control of the external coupling path length. In synchronized state, both lasers operate with significantly reduced timing jitter with respect to their free-running values. Finally, under specific conditions, the repetition rate locking is accompanied by partial mutual coherence between the lasers, as indicated by the formation of interferometric fringes.