Resonant MEMS Accelerometer With CW Laser Excitation

A silicon MEMS resonator which forms an optical cavity with its package is self-excited and interrogated with a CW laser beam at telecom wavelengths delivered to the device through optical fiber. Self-oscillation at 68 kHz occurs with a buckled resonator for laser powers >7 mW. After removal of polarization effects from fiber motion, the resonant frequency is found to vary with acceleration with a scale factor of 0.13 Hz/g even in the absence of an applied internal electric field. This surprising sensitivity is due to spatial variation of the absorbed power within the cavity and is consistent with a simple model of the device. As initially fabricated, self-oscillation occurs over a limited 1.5 degrees C temperature range but with a SiN antireflection layer on the outer surface, the device can self-oscillate continuously from 0 to 80 degrees C. A fractional bias instability <10(-9) is obtained by minimizing fiber vibration. A second, higher frequency mode can also be self-excited. [2020-0142]