Research On Fiber Grating Vibration Sensing Technology Based On Erbium-doped Fiber Laser

Fiber laser has been paid wide spread attention from the beginning for its many advantages, such as low threshold, high efficiency, good reliability and compact structure,and has been widely used in the field of optical communication, aerospace, military affairs and industry. As a fiber grating vibration sensor, Er-Doped Fiber Laser(EDFL)has become the main direction of research, and for its superb performance, it has been applied in sensing applications, such as temperature, strain, stress, pressure.This thesis firstly has studied the principle of fiber laser, and has derived the rate equation of EDFL from the view of the theory of laser oscillator based on three-level structural model of erbiumion. Three output methods of single-longitudinal-model laser have been introduced, standing wave interference and modeselection theory of saturable absorber have been emphatically analyzed, and the fundamental of fiber grating sensor testing and demodulation technology have been briefly introduced.Then, this thesis has designed an Er-doped fiber ring laser, and obtains two major parameters that affect the output power of EDFL by simulated calculation of the output characteristics of laser ring cavity, which are Er-doped fiber length Land coupler ratio R.When L and R take the optimal values, the output characteristic of EDFL is optimum.Next, after the optimization simulation of the output characteristic of EDFL, the optimal length of Er-doped fiber can be get as 2.5 m, and the optimal coupler ratio can be get as 90%. After optimization, the maximum output power has improved by 6.26 m W,and the slope efficiency has improved by 3.42%, and the optimization effect is remarkable. Add an erbium-doped fiber without pumped in laser as saturableabsorber to output single-longitudinal mode laser.Finally, simulations with edge filter based on long period fiber grating are performed, and wide demodulation range can be get. The demodulation range and sensitivity remain the same when increasing the bandwidth of optical FBG. Compared with the center wavelength of FBG and that of output laser, the sensing performance of the sensor is better.