Theoretical And Applied Study Of The Fiber Bragg Grating Based On Evanescent Wave

Biochemical information sensors based on fiber Bragg grating (FBG) has become ahot topic in the research of the crossdisciplinary of bio-optical. The basic principle is tomeasuring the small changes of surrounding refractive index (SRI) by evanescent wave,then estimating the parameters to be measured or ascess the status parameters of thebiochemical process indirectly. This kind of sensor can be also named evanescent wavesensor. In the pesent study of evanescent wave FBG sensors, only the drifting of theresonance wavelength on the change of the refractive index measurement (non-linearrelationship) was used, but the amplitude of the resonant peak didn’t be full used. Besides,due to any biomedical and biochemical reaction phenomenon is accompanied by changesin temperature, there is lack of the research of the impact of temperature. Therefore, theevanescent wave FBG sensors must take the cross-sensitivity of the temperature-refractiveindex into account to make sure the practical applied correctly.The mechanism of the amplitude of resonance wave in eanescent wave FBG sensorswas researched in this paper. And on this basis, a single-side corrosion evanescent waveFBG refractive index sensor was designed to resolve the problem of the influence of thetemperarue in refractive index measurements, which has high refractive index sensitivity.Finally, the designed sensor was applicated in the measurement of sucrose solutionconcentration. The main research contents were as following through the theoretical andexperimental research:(1) The two kinds of cladding corrosion and core corrosion evanescent wave FBGsensors were constructed. The theoretical formula of the resonant wavelength amplitudewith SRI in different corrosion depth was obtained in this paper. The normalizedreflectivity of the core corrosion FBG sensors was acquired.(2) The experimental system was designed and constructed, which was applied to themeasurement of the concentration of sucrose solution. With increase of SRI (less than thecladding refractive index) and corrosion depth, the energy trapped in the fiber can bereduced, then the evanescent wave can be in-depth interact with the external medium.Thus the sensitivity of FBG refractive index sensor based on the evanescent wave wasimproved.(3) The single-side corrosion FBG refractive index sensor based on evanescent wavewas produced. With its unique structure, by the method of numerical analysis of sensitivity matrix, a high sensitivity refractive index sensor was obtained which eliminated the effectsof temperature.(4) The experimental system with temperature and refractive index changingsimultaneously was set up. The produced sensor was applied in measurement of sucrosesolution and its temperature. Experiments results showed that with the increase of therefractive index of sucrose solution, the Bragg wavelength increase linearly. Refractiveindex sensitivity of sucrose solution can be reach at5.42nm/riu. The improved sensor caneliminate the impact of temperature changes on the concentration measurements of sucrosesolution effectively.This project can not only provide powerful means for the various refractive indexchanges of the microscopic mechanism research of the biochemical processes, but can alsopromote the fiber grating biochemical sensor to higher refractive index sensitivity, bettertemperature uncorrelated.