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(a) Optical image of a fully integrated AlN optomechanical resonator. Light is coupled in and out of the chip using grating couplers. (b) False-color scanning electron micrograph of the fabricated AlN ring resonator (in green). The coupling waveguide is denoted in red. (c) Theoretical resonance frequencies of the radial-contour modes of the AlN ring resonators as a function of the outer radius of the ring. The inner radius of the ring is 32.6 μm. For an outer radius of 37.6 μm, the theory predicts a 1st order (I) radial-contour mode at 44.9 MHz and a 2nd order (II) radial-contour mode at 1.05 GHz. The insets show the numerically simulated displacement profiles for the two modes, respectively (not to scale).
(a) Optical transmission spectrum of a released AlN optomechanical ring resonator measured in air with −20 dBm of input power before the input grating coupler. The free spectral range is 5.0 nm. (b) Zoom-in of one resonance at 1544.85 nm with a fitted linewidth of 12 pm, corresponding to an optical quality factor of 125 000. The optical resonance is near critically coupled with an extinction ratio of 18 dB.
(a) Optically transduced RF spectrum of the mechanical modes of the AlN ring resonator measured in air with an input power of 3 dBm. Three mechanical modes are found at 30.6 MHz, 47.3 MHz, and 1.04 GHz. The inset is a measurement at +15 dBm optical power before the input grating coupler, showing back-action induced self-oscillations of the fundamental radial-contour mode (47.3 MHz). (b), (c), and (d) are the zoom-in spectra of the resonance at 30.6 MHz, 47.3 MHz, and 1041.5 MHz, respectively. The fitted (red lines) quality factors are 1000, 1742, and 2473, respectively, for the three mechanical modes measured in air. The inset in (b) is the numerically simulated displacement profile for the wine-glass mode (circumferential number n = 4) at 30.6 MHz.
Properties of the observed mechanical modes: simulated (superscript s) and experimental (superscript e) frequencies, effective modal mass (m eff), measured quality factor (Q m), and displacement sensitivity () of the ring resonator with inner radius Ri = 32.6 μm and outer radius Ro = 37.6 μm.
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