Broadband Optomechanical Accelerometer Reaching the Thermomechanical Limit Based on Suspended Si₃N₄ Membrane Resonator

Acceleration measurement is widely used in military, civil, and industrial applications. However, it is difficult for traditional microelectromechanical systems (MEMS) accelerometers to combine high sensitivity and large bandwidth. Therefore, we propose a Fabry-Perot (F-P) optomechanical accelerometer based on a suspended Si ₃ N ₄ membrane resonator. We develop an optical excitation scheme to investigate the response of the resonator and a separate laser interferometry measurement system to achieve highly sensitive displacement readout. The single thermomechanical vibration mode of the resonator enables precise conversion from displacement to acceleration. The accelerometer exhibited an acceleration sensitivity of 0.72 μg/√Hz at 412.59 kHz, reaching the thermomechanical limit. Then, we focused on studying the relationship between optical power and optical shot noise and reducing the shot noise by tuning the optical power, which increased the accelerometer’s 3 dB bandwidth by an order of magnitude from 1.56 kHz to 15.34 kHz. The displacement sensitivity of the measurement system is optimized to 2.5 fm/√Hz. This sensing platform and optical power tuning method lay a certain foundation for the development of high frequency, high sensitivity, and broadband optomechanical accelerometers.