Study On Solution Concentration Sensing Technique Based On Long Period Grating

Concentration is an important parameter of solution. It is important to measurement and control towards solution concentration in the areas of paper making, chemical, refine sugar, food, medicine and so on. Fiber grating has the advantages of electric insulation, resistance of the interference of electromagnetism, anti-erosion, small volume, light weight, high sensitivity, strong repetition and so on. It can fetch up the disadvantages in traditional measurement. Thus it's a promising sensor of solution concentration.This paper takes long period grating (LPG) as the object. We study the theory of LPG and sensing technique. We propose the measurement towards solution concentration using LPG. We study on the solution concentration sensing theory and simulation. Finally we take an experiment of LPG sensing. The paper generally introduces the study of making and implication of fiber gratings. We deduced the coupling between the guided mode and the cladding mode. We also introduce the calculation of guided mode,cladding mode refractive index and coupling coefficient. We study the effect of grating parameter on the spectrum. The formula of resonance peak shift is deduced. We have the sensing characters with different parameters of LPG under the simulation using Matlab.The paper designs a solution concentration sensing equipment using different LPGs, and different concentrations of a set of NaCl are measured experimentally. The relationships of LPGs'resonance wavelength and concentration are all non-linear. The function of resonance wavelength and NaCl concentration can be deduced from experiment data and formula of LPG refractive index sensing, and the max error is 0.007 nm; Different LPGs have different effective sensing areas; The sensitivities of LPGs are different when NaCl concentrations are at low concentration and high concentration. So when the solution concentration is measured using LPG, LPG should be selectedreasonably according to different solutions and different concentration spans. The sensing of solution concentration can be proceeded after calibration.