Photonic Generation of Ultra-Stable Microwaves from a Microcavity Soliton Optical Frequency Comb via Optical Closed-Loop Injection Locking and Frequency Division

To address the challenges of complex structures, high costs, and difficulties in engineering deployment faced by traditional optically generated ultra-stable microwave systems, this paper proposes and experimentally demonstrates an ultra-stable microwave generation scheme based on microcavity soliton optical frequency combs. The scheme employs optical closed-loop injection locking technology to stabilize the repetition frequency of the optical frequency comb and achieves efficient conversion from the soliton optical frequency comb to ultra-stable microwave signals through low-noise photodetection and an electrical frequency division chain, combining the system simplicity of passive injection locking with the high stability of closed-loop feedback. The experiment generates multiple low-phase-noise frequency outputs spanning from the X-band to the L-band: the locked repetition frequency achieves a phase noise of −40 dBc/Hz at a 1 Hz offset frequency, representing an 80 dB reduction compared to the free-running state; the Allan deviation reaches 1.8 × 10−13 at an integration time of 0.1 s, improving by four orders of magnitude over the free-running case; the standard deviation of frequency fluctuations over 10 h is merely 8.3 mHz. The phase noise of the divided signals at a 1 Hz offset frequency is reduced by at least 80 dB compared to the free-running divided signals. The closed-loop feedback section of the system requires no high-frequency mixers or complex servo systems, greatly suppressing the introduction of electrical noise. It features full-system integration potential and provides a complete technical solution and experimental basis for the engineering deployment of high-performance, miniaturized, low-cost ultra-stable microwave sources.