A multi-material Q-boosted low phase noise optomechanical oscillator

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 Q-boosting 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.