Research On Key Technologies Based On Fiber-optic Sensing Water Quality Monitoring System

Water quality detection based on optical fiber technology has the advantages of high sensitivity,fast detection speed,can realize real-time online monitoring,distributed and quasi distributed monitoring and other advantages,is widely used in the detection of water quality and water quality sensing field;optical fiber sensor can realize multi parameter nondestructive and non pollution monitoring,easy miniaturization and intelligent,is a kind of water quality detection promising sensor.In this paper,proposed and studied based on Sagnac fiber loop mirror with high sensitivity and temperature sensor based on cascade cycle,different length of the LPFG refractive index sensor design,modeling,simulation and optimization,the influence of spectral characteristic parameters of the device on the filter and sensor are discussed in detail.The main innovation and research contents are as follows:(1)The high sensitivity of the temperature sensor based on fiber Sagnac loop mirror is designed and studied through the theoretical research on temperature drift spectrum derived the theoretical formula,the sensitivity sensitivity of temperature sensor based on the vernier effect of 9.80nm/?,than the first temperature sensor,the temperature sensitivity is 1.737nm/?,increased by about 5.64 times,and the the simulation with the Matlab software;(2)A new type of refractive index sensor with high sensitivity is presented,the refractive index sensor composed of two LPFG with different parameters is analyzed and studied,and the influence of cascade LPFG on the sensitivity of the refractive index is analyzed,the simulation experiment was carried out in the OptiGrating software platform,the simulation results of sensing properties of the refractive index of LPFG,for the NaCl solution,the interference wave wavelength shifted from 1690 nm to 1686 nm,the refractive index sensitivity of 90.91nm/RIU.For sucrose solution,when the concentration is from 6% to 50%,the change of wavelength is about 15.2nm,the refractive index change is 0.0786,and the refractive index sensitivity is 193.384nm/RIU.When the concentration is more than 50%,the wavelength change is very large,and the wavelength changes little when the concentration is less than 50%.This conclusion is consistent with the known results.The refractive index sensor has high sensitivity,which can accurately reflect the spectral change of water quality turbidity.(3)On the basis of the above two points of 2,3,a new temperature sensor and a refractive index sensor are designed,to design a real-time detection system based on optical fiber sensing system,because the temperature and refractive index are measured separately,so there is no cross sensitivity problem,the results of the study show that the system can achieve effective detection of water quality.