Abstract
The three-layer structure model of the fiber Bragg grating is proposed in this paper. And through experimental study and reasoning calculation to verify the three layer structure of the optical waveguide model, so the sensitivity characteristic of the Bragg wavelength to the refractive index of chemical solution is obtained. And the relationships between the concentration and the shift of Bragg wavelength of sucrose, ethanol, and Nacl solution are achieved. Finally the shifts of the Bragg wavelength with the external concentration are obtained by experiments. A kind of simple structure, small size, good stability, high sensitivity chemical concentration sensor is obtained.
Highlights
The concentration of solution is considered as one of the integrated indicators of medium solution
At present there are mainly two kinds of fiber grating sensors used for measuring the refractive index change, fiber Bragg grating (FBG) and long period fiber grating (LPFG) [5]
As a result of the coupling based on the core mode and cladding mode, the external refractive index change will have a greater impact on fiber cladding mode transmission properties; the long period fiber grating has a larger sensitivity
Summary
The concentration of solution is considered as one of the integrated indicators of medium solution. The concentration measurement and control of solution is widely used on papermaking, chemical, sugar production, food industry, environmental monitoring, etc. It is the important technical means guarantee product quality and improve the quality of products. At present there are mainly two kinds of fiber grating sensors used for measuring the refractive index change, fiber Bragg grating (FBG) and long period fiber grating (LPFG) [5]. The sensor has the advantages of simple structure, high precision, low cost, eases of reuse, can realize on-line measurement and so on.
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