Fiber Optic Vibration Sensor Based On Fiber Laser

In recent years, with the rapid development in areas such as aviation, aerospace, bridges, civil construction, the dynamics vibration problem has become more complicated. So the demand of vibration sensors with high precision, sensitivity and other performance is increasing. Now electromagnetic vibration sensors have been widely used in many areas, which can not meet these requirements. Therefore, the research and exploitation of new and higher quality vibration sensors has become particularly important. In this paper, a new vibration sensor based on fiber laser is proposed and fabricated. Its response characteristics have been tested. The details are described as follows:(1) Development and the classification of fiber lasers and design principle of DBR fiber laser are briefly introduced. Then Fiber Bragg Grating (FBG) is photowritten by use of 193nm ultraviolet laser scanning technology in this thesis. Using the technology, a Distributed Bragg Reflector (DBR) fiber laser is fabricated. The total length of the DBR fiber laser could be as short as 14mm, which is the shortest as reported so far, while the output power of the laser could still reach up to 2.66dBm.(2) For the first time, fiber-optic vibration sensor, based on orthogonal polarization dual-frequency DBR fiber laser, is proposed. Its principle is that the acceleration is converted to polarization beat frequency of optic fiber laser and the acceleration is obtained by monitoring beat signal. Relationship between DBR fiber laser beat frequency changes and the acceleration is deduced. The expression of sensitivity is obtained and we have discussed the factors, which have an impact on natural frequency and sensitivity of the sensor.(3) Two vibration sensors based on optic fiber laser with different parameters have been fabricated and their response characteristics are tested. We have produced two optic fiber vibration sensors with natural frequency of 129Hz, 131 Hz and sensitivity of 194MHz/(m/s~2), 365MHz/(m/s~2), respectively. The results show that the new fiber-optic vibration sensor has a high sensitivity response to acceleration, which is much higher than sensitivity of commercial piezoelectric accelerometer (1000mV / g).