  In this paper, a novel coarse-to-fine optical MEMS accelerometer based on the
Fabry Perot (FP) interferometer is proposed. The mechanical structure consists
of a proof mass that is suspended by four L-shaped springs. The deflection of
the proof mass due to the applied acceleration is detected using two FP
cavities which comprise the optical system of the device. Using coarse-to-fine
measurement and the dual-wavelength method increases the sensitivity of the
accelerometer as well as the linear measurement range simultaneously. The
optical simulation shows that the sensitivity of the proposed device is 10
times as high as that of a similar optical MEMS accelerometer with one FP
cavity. In addition, the proposed optical system is insensitive to the
displacements of the proof mass in orthogonal directions as a result of which
cross-axis sensitivity is considerably reduced. The minimum feature size of the
structure is 15 um and the optical signal is conducted completely through the
optical fibers, facilitating the fabrication of the device. The simulation
results are as follows: mechanical sensitivity of 190 nm/g, optical sensitivity
of 8 nm/g, linear measurement of 5 g, and first resonance frequency of 1141 Hz.
