Study On The Hybrid Fiber Grating Sensor Technology

The Fiber Bragg Grating (FBG) is a sensor based on fiber grating, and which isused to measure the stress, temperature, refractive index (RI) field area outside ofgrating, whose sensing element is FBG. In recent years, research of Fiber Gratingsensor mainly concentrated on Fiber Bragg Grating (Fiber Bragg Grating, FBG) andLong Period Fiber Grating (Long Period Fiber Grating，LPFG). But, there has alwaysbeen temperature, strain, refractive index, bending and other physical quantities crosssensitivity problem in the application of FBG and LPFG. This makes the measurementprecision is greatly reduced. Therefore, to solve the problem of cross sensitivity in theprocess of measurement is important.Scholars at home and abroad have put forward many solutions to solve the crosssensitivity problem in sensing applications. They all have their special characteristics.Overall, all of them are need a combination of two or more than two kinds of sensorsto solve this problem. In this context, the paper deeply studies the responsecharacteristics of the transmission spectrum of the new hybrid fiber Bragg gratingbased on FBG and LPFG. This paper also summarizes the relative mechanism and thesensing rules. And a hybrid fiber grating sensor with high sensitivity is got. Finally,this sensor was applied in the simultaneously measurement two parameters of sugarsolution concentration and temperature. The main research content in this paper is asfollowing:(1) According to the theory analytical of the FBG and the LPFG’s temperatureand the external medium refractive index sensing characteristics, the influence ofFBG and LPFG’s main structural parameters to temperature and external refractiveindex of rate sensitivity factor is got. And have designed some different structureparameters of experiments to verify the theory.(2) Research on the theories of the sensing characteristics of hybrid fiber gratingsensor. The reasons for temperature and refractive sensing in hybrid fiber gratingsensor are analyzed. Then the matrix comparison expression of temperature and theexternal medium refractive index is got, when hybrid fiber grating sensorsimultaneous measurement of temperature and the external medium refractive index.(3) The hybrid fiber grating sensor based on FBG and LPFG was produced.Because of its unique structure, using the way of numerical analysis of sensitivity matrix, than by means of experiments, we can obtain a high sensitivity temperatureand refractive index sensor which can solve the problem of temperature and refractiveindex effects of cross sensitivity.(4) Setting up the experimental system of temperature and the external mediumrefractive index changing at the same time. The produced sensor was applied insimultaneously measurement of sugar solution refractive index and temperature.Experiments results showed that the root mean square error deviation of the measuredsucrose refractive index from the applied sucrose refractive index was±2.18RIU,and the root mean square error deviation of the temperature from the appliedtemperature was±0.39℃. This hybrid fiber grating sensor can effectively solve theproblem of the external medium refractive index and temperature cross sensitivity.This project can not only provide an effective multi parameters simultaneousmeasurement method for the study biochemical process micro-mechanism in the fieldof biomedicine and biochemistry, but also can lead the direction of development ofthe fiber grating biochemical sensor to higher temperature and refractive indexsensitivity.