Chip-Scale Optomechanical Frequency Comb with a 1-70 GHz Span

An optomechanical frequency comb arises from the nonlinear interaction between optical and mechanical modes in a cavity, with its repetition rate set by the mechanical frequency. Despite promising applications in the microwave domain, previous demonstrations have been limited in spectral range due to inherently low mechanical frequencies. Here, we report an optomechanical comb with a record modulation span from 1 to 70 GHz, achieved by harnessing the strong optomechanical nonlinearity of a 2.5-μm-radius silicon carbide microdisk. With just 1 mW of dropped optical power, radiation pressure from a continuous-wave pump drives strong phonon lasing, generating 42 phase-locked harmonics with 1.655 GHz spacing. The combination of such broad bandwidth, low phase noise (-132 dBc/Hz at 1 MHz offset frequency), and frequency stability (<10^-7 at 1 s of averaging time) positions this ultracompact optomechanical comb as a powerful platform for diverse applications.