Research On Sensing System Based On Composite Cavity Mode-locked Fiber Laser

In recent years,with the continuous development and maturity of optical fiber sensing technology,optical fiber sensor has been developed rapidly because of its superior performance such as strong antielectromagnetic interference ability,small size,low cost and strong corrosion resistance.Because it can be used to detect many parameters,such as vibration,strain,acceleration and so on,it has been widely used in military,electric power,aerospace,bridge structure health monitoring and other fields.fiber laser,as the main light source of fiber sensing system,has the advantages of good tunability of output laser wavelength,light weight and good compatibility.at the same time,the output laser of fiber laser can be coupled to the corresponding sensor through optical coupler,so fiber laser can be widely used in the field of fiber sensing.In addition to the applications in the field of fiber sensing,fiber lasers are also the main devices in optical fiber communication systems,such as multi-wavelength fiber lasers,mode-locked fiber lasers and so on,which are also very important in ultrafast optics,optical information detection and processing,biomedicine and other fields.Because of the wide application of fiber laser in the field of fiber sensing and fiber communication,the research on fiber laser has also attracted the attention of scientific research staff.The main research contents of this paper include a fiber grating sensing system based on active modelocked fiber laser,which uses laser active mode-locked to realize the location of fiber grating sensor and the detection of wavelength shift.By changing the modulation frequency,the system can selectively lock the mode to different resonators,so it can locate the FBG sensors in different positions,and realize the detection of the wavelength changes caused by the strain or temperature of the FBG sensors on the same optical path.the working principle of the system is theoretically analyzed,and the temperature sensing is taken as an example to verify the system,which proves the ability of the system to detect different fiber grating arrays in wavelength and space.At the same time,a sensing system based on compound cavity mode-locked fiber laser is proposed.The system uses Fabry-Perot laser diode and fiber grating to form the resonator of the laser,and the Fabry-Perot cavity(F-P cavity)composed of two fiber gratings is used as the outer cavity of the system.Fiber Bragg grating,Fabry-Perot laser diode and laser gain part together constitute the composite cavity fiber laser.In the system structure,Fabry-Perot laser diode as active mode-locked modulation device,envelope modulation to achieve the purpose of active mode-locked,and achieve the use of active modelocked mode in the composite cavity fiber laser weak reflection fiber grating sensor location research.At the same time,the system uses the laser beat frequency technology to measure the experimental results,and converts the measurement of optical signal into the measurement of electrical signal,which makes the data processing more convenient.The proposed structure has the advantages of easy operation,low cost and good compatibility,so it has a good application prospect.