Stable 10 GHz microwave synthesis via partial optical frequency division

Synthesis of low-noise microwaves is desirable in a wide variety of scientific and engineering fields. Optical frequency division with frequency combs has been a key part in the realization of ultrastable microwave signals. However, fully self-referenced frequency combs are complex and involve several nonlinear processes for implementation of the f-2f interferometer. In this paper, we provide a novel approach for generation of ultrastable microwaves by stabilizing the comb spacing, while the offset frequency of the comb is free-running. This is achieved by mixing the beats of a frequency comb with two continuous wave (cw) lasers separated by 1.3 THz, which are PDH locked to a single reference cavity. We demonstrate the generation of stable 10 GHz microwaves with −140 dBc/Hz phase noise at 10 kHz Fourier frequency and 5·10
⁻¹³
level Allan deviation instability at 0.3 s. This work projects the potential of future compact microwave generation with low power consumption.