Ultra-sensitive monolithically integrated tri-axial fiber-optic accelerometer with a nano-g level noise floor

In this paper, we propose and demonstrate a nano-g level monolithically integrated tri-axial fiber-optic accelerometer. The tri-axial sensing units are integrated into a silicon-based chip, incorporating improved spring-mass structures that significantly increase sensitivity. Moreover, the chip behaves with a uniform thickness of 460 μm, greatly simplifying the fabrication process. Acceleration signals are retrieved using fiber-based Fabry-Perot interferometers (FPIs) and optical phase demodulation. Within the operating bandwidth of 1~64 Hz, the sensitivities of the in-plane and out-of-plane sensing units exceed 43.6 dB (151.4 rad/g) and 42.8 dB (138.7 rad/g), respectively. The average noise floor of the tri-axial units is measured to be as low as 22.82 ng/Hz^1/2. The results indicate that the proposed fiber-optic accelerometer is highly promising for applications in low-frequency micro seismic monitoring applications.