Asymmetric phononic frequency comb in a rhombic micromechanical resonator

As an analog of the optical frequency comb, the phononic frequency comb has been demonstrated in mechanical resonators recently. In this Letter, we generate the frequency comb in a rhombic micro-resonator with stiffness parametrically modulated by low-frequency pumping. Interestingly, this comb exhibits the asymmetry in the amplitude, i.e., the amplitudes of comb fingers on either side of the central comb finger decay with different rates. With a parametrically modulated model, we analyzed in detail the asymmetry in the frequency comb and accurately captured the reason for the asymmetry. Furthermore, the asymmetry of the frequency comb can be adjusted experimentally. These results provide a theoretical basis for manipulating the comb fingers and are expected to open the door for potential applications of the frequency comb.