Enhancing microcomb efficiency via pump recycling in a chip-integrated gain medium

Continuous-wave (CW) laser-driven integrated Kerr microresonators enable broadband optical frequency combs with high repetition rates and low threshold power, in a compact footprint. A drawback of such microcombs is the low conversion efficiency from the pump laser to the comb lines, which is often in the few percent range or below. In recent works, improved conversion efficiency has been demonstrated by leveraging soliton crystal states [1], interferometric back-coupling to suppress the residual pump light [2], or tuning the resonance frequency of the pumped mode [3]. While these approaches achieve improved conversion efficiency, they add complexity to the design and operation of the system, relying on non-deterministic states, dynamic control, and/or a potentially reduced number of comb lines.