An Opto-mechanical MEMS Accelerometer with Noise Floor of 40 ng/Hz^1/2

Miniaturized accelerometers are in high demand for consumer electronics, acoustic monitoring, and unmanned aerial vehicles. However, there is a tradeoff between accelerometer resolution and size, which poses a major challenge. In this study, we introduce an optomechanical microelectro mechanical system (MEMS) accelerometer based on a Fabry-Perot (F-P) microcavity. The F-P microcavity consists of a fixed hemispherical mirror and a harmonic oscillator made of monocrystalline silicon. Despite its small size (only 10 mm), the MEMS accelerometer exhibits an acceleration noise floor of 40 ng/Hz$^{1/2}$ at 180 Hz, a bandwidth of 500 Hz (-3 dB), and a dynamic range of 80 dB. To suppress dominant laser intensity noise and the disturbance of temperature and pressure on the optical fiber, a balanced detection method is employed, reducing the overall noise floor from 250 ng/Hz$^{1/2}$ to 40 ng/Hz$^{1/2}$, which approaches the mechanical thermal noise limit (37 ng/Hz$^{1/2}$). These results demonstrate that the opto-mechanical coupling between the oscillator and microcavity is an excellent platform for precision measurement and opto-mechanics, benefiting from its extremely small mode volume and ability to restrain photons.