Monolithically Integrated On-Chip Dual Mode-Locked Lasers in InP-Based Generic Foundry Platform

Summary form only given. Optical frequency combs are a promising technology for widespread applications in precision spectroscopy, microwave generation, frequency metrology, and telecommunications. In recent years, there has been significant demand for chip-scale sources to generate not only single but dual combs. Such dual-comb spectroscopy (DCS) produces two mutually coherent and broadband optical frequency combs with slightly different and preferably controllable repetition rates. The heterodyne beating between these two combs gives a sequence of beat notes enabling high-speed sampling of molecular absorption spectra. However, current Kerr nonlinearity-based microring resonator solutions require external high-power CW pump lasers and the repetition rates are not adjustable. In this paper, we propose and experimentally demonstrated the two-element mode-locked laser array developed in a cost-effective generic foundry approach. It is electrically driven and the comb spacing is slightly tuneable. The two mode-locked lasers are mirror images to each other and symmetrically deployed. Each mode locked laser is composed of one saturable absorber (SA), two SOA gain sections, electro-optic phase modulators (EOPM) and passive waveguides. These two lasers are optically coupled through an MMI coupler and the combined optical signal can be collected at the angled waveguide output. The photonic IC is physically placed on and electrically connected to a specifically designed submount. Assembled with such a RF-compatible submount, this semi-packaged photonic integrated circuit supports passive and hybrid mode locking. In passive mode locking, the repetition rates of the two ring lasers correspond to 12.420 GHz and 12.423 GHz, respectively, which shows the potential as chip-scale DCS generator with the narrow RF linewidths (<; 200 kHz) and the controllable relative repetition rate.