Research Of Solution Concentration Fiber Sensor Based On Long Period Fiber Grating

The concentration of the solution is one of the most important physical parameter of the liquid solution, with the important value of measurement and monitoring in the industrial, agricultural production and scientific research. The optical fiber sensing technology with high sensitivity, small volume, easiness to long distance transmission, capable of achieving real-time sensing and suitability for harsh environment has made it widely applications and broad prospect in the sensing field of solution concentration. At present, the linear relationship between the concentration of the solution in a certain range and refractive index is one of the most important principles that used in the optic fiber sensing of the solution concentration. This paper focuses on solution concentration fiber sensor based on long period fiber grating (LPFG) due to characteristics of sensitivity to external environment, simple structure, stable performance, etc. Main content of this paper is as follows:Firstly, a large number of literatures have been consulted in and analysis of the advantages and disadvantages of various solution concentration sensors has been discussed. On the basis of previous studies, two kinds of effective schemes based on LPFG is proposed.Secondly, this article has carried on the analysis and research on the theory of long period fiber grating, including the the coupled mode theory, fabricating methods and the formation mechanism of LPFG. Then the spectral properties of LPFG and refractive index sensing characteristics are analyzed by a Matlab program, which shows the changes of the transmission spectra and the refractive index sensing characteristics that caused by LPFG parameters’change. The analyses lay a solid foundation for the design of LPFG solution concentration sensor, which has important theoretical guiding significance for the optimization design of LPFG solution concentration sensor and application.Thirdly, in view of on solution concentration sensing applications, the simulation and analysis have been carried on. Also, the period and the model parameters of LPFG are discussed in detail, the sensor with a relatively optimal method and much higher performance sensitivity has been designed. The sensitivity of the separation of dual resonant peaks of LPFG has reached to1100nm/RIU, which greatly increased the sensitivity of solution concentration sensor.Last, fiber taper seeded long-period grating pair as a highly sensitive refractive-index sensor is studied by experiment, and the sensitivity reached to147nm/RIU. Moreover, the experiment on the method of corrosion of cladding to optimize the design of the sensor is carried out, and the sensitivity reached to147nm/RIU, which is7times better than general LPFG sensors. This scheme is of great significance in practical applications.