Fig. 1. (a) Schematic of the silicon carbide (SiC) cavity optomechanical system and its operating principle. (b) Scanning electron micrograph of a 4.5-μm-radius microdisk with on-chip waveguide access. The 4H-SiC microdisk has a device thickness of 600 nm, sitting on a 2-μm-thick silicon dioxide pedestal with an approximate undercut width of 3.4 μm. (c) Simulated mechanical frequency of the fundamental radial breathing mode (RBM) as a function of the radius. The inset displays the corresponding mechanical displacement profile based on finite element simulation: Young’s modulus EY=535GPa, Poisson’s ratio ν=0.183, and mass density ρ=3210kg/m3.

Fig. 2. Experimental setup for the optomechanical measurement, where the slow photodetector (MHz-PD) is to identify optical resonances and the fast photodetector (GHz-PD) is for the mechanical characterization. VOA: variable optical attenuator; WDM: wavelength division multiplexer; PD: photodetector; and ESA: electrical spectrum analyzer.

Fig. 3. (a) Scanning electron micrograph of a waveguide-coupled SiC microdisk. The inset shows a close-up view of the suspended microdisk. (b) Representative transmission scan of a suspended 4.5-μm-radius microdisk, with two adjacent azimuthal orders of the TE00 mode family identified with a free spectral range (FSR) of 4.2 THz. (c) Zoom-in plots of the two TE00 resonances highlighted in (b), both of which exhibit mode splitting. The red dashed line represents numerical fitting using a doublet model, revealing intrinsic quality factors in the range of (0.5–1.2)×106.

Fig. 4. (a) Linear transmission of a suspended 4.3-μm-radius SiC microdisk resonator. The insets are the zoomed-in resonances for the TE00 and TE10 modes at 1592 nm and 1610 nm, respectively, with the red dashed lines representing numerical fitting based on a doublet model. (b) Optically transduced electrical spectrum (blue curve) of the fundamental radial breathing mode (RBM) measured with an approximate dropped power of ∼2.5μW. The gray trace corresponds to the background noise level of the high-speed photodetector (i.e., no optical input). The resolution bandwidth of the ESA is set at 500 Hz. (c) Close-up view of the fundamental RBM around 950 MHz with a damping-limited mechanical quality factor of 19,200 at room temperature (resolution bandwidth of ESA set at 20 Hz). The left and right y-axes correspond to the measured data in (b) converted to the voltage and displacement domains, respectively. The red dashed line is numerical fitting based on a damped harmonic resonator model.

Fig. 5. Summary of measured mechanical quality factors (Qm, left axis) and frequencies (fm, right axis) of SiC microdisks with different radii. The degradation of the mechanical Qm with increased radius is mainly attributed to the reduced undercut ratio.

Fig. 6. (a) Evolution of the photodetected RF spectrum near the resonant frequency of the fundamental radial breathing mode (RBM) as a function of the increased optical power. (b) Close-up view of the RF spectrum corresponding to a dropped power of 32 μW (resolution bandwidth of ESA set at 5 Hz). (c) Zoomed-out RF spectrum corresponding to the same optical dropped power as in (b) (i.e., 32 μW) but with resolution bandwidth set at 5 kHz, revealing harmonics of the fundamental RBM as well as a secondary mechanical mode centered at 3.8 GHz. The inset plots a closed-up view near the 3.8 GHz mode (resolution bandwidth of the ESA set at 2 kHz), where the sharp spike (on the left shoulder of the 3.8 GHz mode) represents the fourth harmonics of the fundamental RBM. (d) Normalized mechanical energy as a function of the optical dropped power with the red dashed line representing a linear fit to the data above the threshold.

Fig. 7. (a)–(c) First e-beam lithography and dry etch to define photonic structures. (d), (e) Second e-beam lithography followed by a selective wet etch to form a suspended microdisk and coupling waveguide. The workflow illustrates the cross-section orthogonal to the direction of light propagation within the waveguide. Thus, the waveguide in (f) is supported by the pedestal layer along its length, as depicted in Fig. 1(a).