Fig. 1. Force diagram of optical force driven optomechanical system with a 2-DOF mechanical oscillator

Fig. 2. PCN-based nonlinear optomechanical system for optomechanical frequency comb measurement. (a) Overall SEM image of nonlinear optomechanical system; (b) SEM image of two mechanical oscillators in the nonlinear optomechanical system; (c) SEM image of curved nonlinear beam of nonlinear oscillators in the device to be measured; (d) design of the nonlinear mechanical oscillator; (e) SEM image of optical evanescent coupling of dimpled fiber taper and device on chip

Fig. 3. Simulation results of different modes in the optomechanical system. (a) Optical resonance modes (top: the odd mode of the first order resonant; bottom: the even mode of the first order resonant); (b) in-plane mechanical oscillation modes of first-order linear mechanical oscillators (top) and second-order nonlinear mechanical oscillators (bottom)

Fig. 4. Measurement setup of the optomechanical system

Fig. 5. Optical transmission spectrum of optical resonator. (a) First two orders optical resonances; (b) resonance of TE_2,e mode with Lorentzian fitting

Fig. 6. Measured RF spectrum of the 2-DOF optomechanical system (insets are FEM-calculated IP modes)

Fig. 7. Observation results of optomechanical frequency comb at TE2,e mode. (a) PSD map of the fundamental IP1 mode of second-order nonlinear oscillator; (b) PSD map of the fundamental IP1 mode of first-order linear oscillator; (c) RF spectra measured in the zone A at the wavelength of 1573.460 nm; (d) optomechanical frequency comb measured in the zone B at the wavelength of 1573.478 nm; (e)-(f) zoom-in views of the dashed squares in Fig. 7(d)

Fig. 8. Observation results of optomechanical frequency comb at TE_1,e mode. (a) Optical resonance of the TE_1,e mode at the input power of 25μW; (b) PSD map of IP1 mode of second-order nonlinear oscillator; (c) PSD map of IP1 mode of first-order linear oscillator; (d) optomechanical frequency comb measured at the zone C at the wavelength of 1531.076 nm; (e)-(f) zoom-in views of the dashed squares in Fig. 8(d) (Ωm2/2π=10.22MHz and Ωm1/2π=13.54MHz)