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

•It is theoretically proved that the −1st comb tooth power is related with the modulation depth and the frequency difference between fm (the modulation frequency) and frep (the free-running repetition rate).•An optical closed-loop injection locking technology is realized using the −1st comb tooth as error signal for the soliton microcomb repetition rate (frep) long-term stabilization.•The SSB phase noise of the closed-loop locked frep have no obvious change in long-term, which is about 20 dB lower compared with the open-loop locking case. And the Allan deviation of the closed-loop locked frep maintains at 1.8 × 10-13@0.1 s for a long time, which improves by three orders of magnitude compared with the open-loop locking case. We demonstrate an optical closed-loop injection locking technology for the soliton microcomb repetition rate (frep) 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 frep locked at an optimal level. After injection locking for 2 h, the single-sideband (SSB) phase noise of the closed-loop locked frep decreases by 20 dB compared with the open-loop locked frep 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 frep 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 frep 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.