Long-term repetition rate stabilization of soliton microcomb using optical closed-loop injection locking

We demonstrate an optical closed-loop injection locking technology for the soliton microcomb repetition rate (f_rep) stabilization. Using the power of the −1st comb line (−1st represents the first comb tooth on the left side of the pump laser) as an error signal, the pump laser frequency is auto-tuned to ensure f_rep locked at an optimal level. After injection locking for 2 h, the single-sideband (SSB) phase noise of the closed-loop locked f_rep decreases by 20 dB compared with the open-loop locked f_rep within the offset frequency range of 20 Hz to 30 kHz. After locking one and a half hours, the Allan deviation of the closed-loop locked f_rep reaches 1.8 × 10⁻¹³@0.1 s, which improves by three orders of magnitude. The experimental results prove the feasibility of the optical closed-loop injection technology for long-term f_rep stabilization. The proposed scheme has excellent locking performance, simple structure and low cost, which has the potential application for stable microwave generation, precision ranging, etc.

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