Composite Cavity Fiber Laser And Its Sensing Applications

In recent years, fiber-optic sensor has been rapid development because of its superior performance. As technology continues to mature fiber grating, fiber bragg grating (FBG) based DBR and DFB fiber laser has become a hot research. Not only as the light source of sensing system, DBR and DFB fiber laser can be used as the sensing element. As the characteristics of grating narrow-bandwidth, high-sensitivity, DBR and DFB fiber laser solved the low signal and noise ratio of FBG. Sensors based on DBR and DFB fiber laser have a high sensitivity on strain, temperature, acoustic, and so on, which arouse people a lot of interesting.We do some research on composite cavity fiber laser characteristics, a modified DBR lasers, and its application in sensing.Firstly, the theoretical analysis of the fiber laser are given to analyze its characteristics based on dynamic and steady state rate equations. Then composite cavity fiber laser is fabricated and its characteristics, such as the laser wavelength, pump threshold, the relationship of the input power and the output power, are measured.Secondly, we focus on the feedback effect of the composite cavity fiber laser. We splice a length of fiber in the end of the composite cavity fiber laser to form another external cavity. The feedback effects, introduced by Rayleigh scattering and the reflection of the fiber end face, are discussed. Lots of simulations are given to show that the light intensity of the fiber laser is depend on the feedback, including the length of external cavity and the feedback coefficient of external cavity. Selected the appropriate parameters, a sensing scheme based on feedback effect can be realised by monitoring the light intensity of the fiber laser.At last, the two kinds of intensity demodulation based sensing schemes of the composite cavity fiber laser are demonstrated experimentally. Firstly, a composite cavity fiber laser is used as a sensing head to measure the acoustic signal. Secondly, the feedback effects of composite cavity fiber laser are used as a sensing scheme and the corresponding acoustic measurement prove its feasibility. The feedback effect based sensing scheme is more flexible and can protect the composite cavity fiber laser effectively. The low cost sensing scheme expect to have broad applications.