Frequency comb in a parametrically modulated micro-resonator

In this paper, we report the frequency comb response experimentally and analytically in a rhombic micro-resonator with parametrical modulation. When the electrostatically actuated rhombic micro-resonator is modulated axially by a low-frequency periodic excitation, a comb-like vibration response with few equidistant positioned fingers in the frequency domain is observed. The finger spacing of frequency comb response is exactly consistent with modulation frequency and the number and amplitude of the fingers can be tuned by modulation strength. A mixed frequency comb with extra comb fingers is further generated when the resonator is modulated simultaneously by two different low-frequency excitation signals. By adjusting the relation of the two modulation frequencies, unequal spacing frequency combs are achieved for the first time, which leads to a more flexible tunability of the comb spacing for different applications. Theoretical analysis based on the dynamic model well explains the corresponding observations.