Study On Fiber-optic Accelerometer Based On MEMS

The combination of Micro-electro-mechanical System (MEMS) and fiber-optic detection technology introduces a brand new direction-MEMS fiber-optic sensor. Compared with the traditional sensor, the fiber-optic sensor based on MEMS shows significant advantages of electrical insulation in detection end, immunity to electromagnetic interference, small size and suitable for long distance transmission etc. In this thesis, a novel fiber-optic accelerometer structure based on MEMS was presented. The sensitive chip was accomplished by micromachining technology and the fiber-optic accelerometer was achieved by the packaging of sensitive chip and dual fiber collimator.First of all, the overview of MEMS technology was given, followed by the present status and ongoing trends of optical MEMS, especially the applications of optical MEMS on accelerometer. Then, the micro-accelerometer was classified and some representative micro-accelerometer structures were given. Based on the former research on MEMS and fiber-optic sensor, a MEMS fiber-optic accelerometer with simple and easily fabricated structure was presented. Secondly, the operation principle of the accelerometer was introduced. Then, the sensitivity of the MEMS fiber optic accelerometer was calculated according to the design requirement. Thirdly, the parameters of the sensitive chip were obtained and optimized in term of the sensitivity, mechanical, optical, electrical and noise characterization. At the same time, the Finite Element Analysis (FAE) tool, ANSYS was employed to simulate the vibration mode and analyze the stress. Finally, the sensitive chip was obtained by the micromachining process such as photolithography, wet etching, bonding and dry etching, deep reactive ion etching (DRIE). After the packaging of sensitive chip and dual fiber collimator, static and dynamic test was carried out. The results show that the resolution of the accelerometer is smaller than 100μg. The dynamic range of the accelerometer is±2g and the bandwidth is 600Hz. In this thesis, the innovation combination of optical detection and MEMS gives a new application on accelerometer, which takes good advantage of optical detection and MEMS. The accelerometer is of low noise, small size and adaptive for long distance transmission and intense magnetic environment. On the other hand, the asymmetric torsion structure implements the modulation of light by the movable MEMS device, where the damping is easily controlled, thus leads the wide bandwidth and good frequency response. The application of dual fiber collimator on the optical detection brings about the high resolution and large dynamic range.At the end of the paper, the fabrication process and the packaging of the accelerometer were summed up and the future wok was discussed.