Bending Sensor Based On Orthogonal Dual-Frequency Fiber Laser

In the present structural health monitoring, a large number of fiber optic sensors has been developed, but most of these sensors are for structural strain, stress, temperature, vibration monitoring and many other parameters, while there are only a few fiber sensors for deformation monitoring of structures. In this thesis, a bending sensor based on orthogonal dual-frequency fiber laser (DBR fiber laser) is fabricated. Its response characteristic has been tested. The details are described as follows:1. The development, classification and characteristics and applications of fiber lasers are briefly introduced. Then the structure of the DBR fiber laser is introduced in detail, the principle of fiber Bragg grating is introduced also. The technology about fabrication of DBR fiber laser is introduced in detail. The DBR fiber laser is produced by using phase mask method, while 193nm ArF excimer laser is used as a photo writing source. Using this technology, a short DBR fiber laser is fabricated.2. The sensing principle of DBR fiber laser is introduced. Then the relationship between polarization mode beat frequency of DBR fiber laser and bending curvature is deduced. Bended along two special directions, output changes of the polarization beat frequency of the DBR fiber laser is deduced. In the experiment, an Er3+/Yb3+ co-doped DBR fiber laser is demonstrated as bending sensor. Bended along two special directions with different curvature, output changes of the polarization beat frequency of the DBR fiber laser is investigated. Experimental results show that the use of DBR fiber laser to measure the curvature is feasible.