Research On Temperature-salt-depth Sensing Characteristics Based On SNS-FBG Cascade Structure

In recent years,fiber optical sensor is small in size,light in weight,and has the advantages of corrosion resistance and electromagnetic interference resistance.It has been widely used in machinery manufacturing,energy mining,biomedicine,chemical sensing and other fields.In the field of marine environmental monitoring,the temperature,salinity and depth of seawater are important physical parameters for marine research.The application of optical fiber sensing technology has received extensive attention in the measurement of marine physical parameters,and it has become a research hotspot in the field of marine environmental monitoring.This paper analyzes the research status of optical fiber sensors in the field of ocean physical quantity monitoring.On this basis,a fiber optic senor for temperature,salinity and depth of seawater based on the SNS-FBG-FBG cascade structure is designed,and the corresponding experimental system is built to test the sensing characteristics of the optical fiber sensor.The main contents of the paper include:Firstly,the corresponding relationship between salinity and refractive index,depth and pressure are studied,and the measurement method of measuring refractive index and pressure to indirectly obtain the parameters of salinity and depth are discussed.The refractive index sensing principle of the Single Mode Fiber-No Core Fiber-Single Mode Fiber(SNS)structure is analyzed,and the fiber bragg grating(FBG)structure is analyzed to study the temperature and pressure sensing principle of the FBG;Secondly,the SNS structure parameters were analyzed by simulation.The FBG temperature sensitized package and the FBG pressure sensitized package structure were designed respectively.On this basis,the overall packaging and protection structure of the fiber optic temperature-salt-depth sensor based on the SNS-FBG-FBG cascade structure is designed;Finally,the optical fiber salinity sensor,the optical fiber temperature sensor,the optical fiber pressure sensor and the fiber optic temperature-salt-depth sensor were prepared,and the experimental system for salinity,temperature,and pressure sensing was built to test the sensing characteristics of the sensor.The independence of different wave valley positions in the fiber optic temperature-salt-depth sensor is verified.By establishing a cross-sensitivity matrix,the sensing spectrum of the fiber optic temperature-salt-depth sensor is demodulated to realize the measurement of salinity,temperature and pressure.