Research On Spectral Characteristics Of Long-Distance Point Sensing Based On Random Fiber Laser

As an important branch of random lasers,random fiber laser has capacity for wide range of wavelength tunability,narrow linewidth,and high power output which has been revealed by related researchers.It has been widely used in the fields of optical fiber sensing,optical imaging,and optical communications because of these unique advantages.Especially in the long-distance optical fiber sensing system,the optical sensing system based on fiber random laser not only has the characteristics of simple structure,antielectromagnetic interference,high sensitivity,but also has the characteristics of short response time,reusable sensor,and accuracy,what's more,it will not be affected by the wavelength drift of the light source and the temperature change of the link.It is very suitable for the safety inspection of long-distance high-voltage transmission lines,railways,oil and natural gas pipelines and other infrastructures.At the same time,the power distribution of the high-order random fiber laser extends to the end of the fiber,which can improve the signal-to-noise ratio of the end sensing signal and realize ultralong-distance point sensing.At present,most researches on optical fiber sensing systems based on random laser focus on long-distance single-point sensing.There is still a lack of in-depth exploration for ultra-long-distance multi-point sensing systems,especially the lack of simulation models that can accurately describe the spectral characteristics of high-order fiber longdistance sensing systems based on random laser.Therefore,aiming at the key issue of the simulation of spectral characteristics in high-order random laser point sensing systems,the research content is as follows:(1)Aiming at the spectral simulation problem of high-order random lasers,this thesis improves the traditional power balance model so that the improved model can describe the spectral characteristics of high-order random laser systems.(2)In order to explore whether the improved model can be used in high-order random laser systems,keeping the first-order half-open cavity structure of the random laser unchanged,by placing the second-order full-open cavity,the second-order half-open cavity and the sensing FBG with an interval of 10 km,Under this three different random laser structures of random fiber laser,the simulation results and experimental results are compared and analyzed.The simulation and experimental results are highly consistent,which verifies the accuracy of the spectral simulation model proposed in this thesis.(3)This thesis uses the improved high-order fiber random laser simulation model to design and implement a 150 km ultra-long-distance multi-point sensor system based on a second-order random laser.The experimentally obtained sensor signal wavelength and strain are fitted linearly.The combined excellent degree is as high as 0.999.Aiming at the problem that the signal-to-noise ratio gap of the sensor signal is too large in the system,the solution of placing the sensor FBG at an interval of 10 km is adopted,which effectively reduces the power gap of the sensor signal and achieves the purpose of system power optimization.The high-order random spectrum simulation model can be used to describe the spectral characteristics of random lasers proposed in this thesis,and its correctness has been verified by multiple sets of experiments,and it has been applied to the design and power optimization of second-order long-distance(150km)multi-point sensing systems.In a short,the simulation model can quickly and accurately calculate the spectral signal characteristics of long-distance multi-point sensing system based on high-order random laser under different sensing distances,providing a reliable platform for designing such a sensing system.