A self-sustained Radiation-Pressure driven MEMS ring OptoMechanical Oscillator (RP-OMO) attaining an anchor-loss-limited mechanical -factor of 10,400 in vacuum has posted a best-to-date phase noise of -102 dBc/Hz at a 1 kHz offset from a 74 MHz carrier, more than 15 dB better than the best previously published mark [1]. While enhanced optical and mechanical both serve to lower the optical threshold power required to obtain oscillation, it is the mechanical that ends up having the strongest impact on phase noise [2], much as in a traditional MEMS-based oscillator [3]. This motivates a focus on increased mechanical -a challenge in previous such devices measured in air-and requires measurement in the absence of gas-damping using a custom optical vacuum measurement system. The improved phase noise performance of these RP-OMOs is now on par with many conventional MEMS-based oscillators and is sufficient for the targeted chip-scale atomic clock application.
A Radiation Pressure driven Optomechanical Oscillator (RP-OMO) comprised of attached concentric rings of polysilicon and silicon nitride has achieved a first demonstration of a mixed material optomechanical device, posting a mechanical Q m of 22,300 at 52 MHz, which is more than 2× larger than previous single-material silicon nitride devices [1]. With this Q m , the RP-OMO exhibits a best-to-date phase noise of -125 dBc/Hz at 5 kHz offset from its 52-MHz carrier-a 12 dB improvement from the previous best by an RP-OMO constructed of silicon nitride alone [1]. The key to achieving this performance is the unique mechanical Qboosting design where most of the vibrational energy is stored by the high-Q m polysilicon inner ring which in turn boosts the overall Q m over that of silicon nitride, all while retaining the high optical Q o >190,000 of silicon nitride material. Simultaneous high Q o and Q m reduces the optical threshold power for oscillation, allowing this multi-material RP-OMO to achieve its low phase noise with an input laser power of only 3.6 mW.
Switching of transducer coupling in aluminum nitride contour-mode resonators provides an enabling technology for future tunable and reconfigurable filters for multi-function RF systems. By using microelectromechanical capacitive switches to realize the transducer electrode fingers, coupling between the metal electrode finger and the piezoelectric material is modulated to change the response of the device. On/off switched width extensional resonators with an area of <0.2 mm2 demonstrate a Q of 2000, K2 of 0.72, and >24 dB switching ratio at a resonator center frequency of 635 MHz. Other device examples include a 63 MHz resonator with switchable impedance and a 470 MHz resonator with 127 kHz of fine center frequency tuning accomplished by mass loading of the resonator with the MEMS switches.
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