The sensitivity of fiber Bragg grating based chemical sensor

The chemical sensing principle based on Fiber Bragg Grating (FBG) is presented. By deriving the relation between effective core index and surrounding index of etched FBG, the relation between Bragg wavelength and concentration of chemical solutions is analyzed, which is demonstrated in the experiment by measuring propylene glycol solutions. The factors influencing the sensitivity of chemical sensing is investigated. The results show that, the sensitivity of the Bragg wavelength of FBGs to the surrounding index can be enhanced with decreasing the diameter of FBGs by etching the fiber with HF solution. The sensitivity can be appreciably enhanced by etching the fiber diameters as small as 5.0 mu m. A maximum sensitivity of 911.8 nm/riu is achieved. Since a shift of 0.01 nm can be detected, this leads to a detectable change of 1.1x10(-5) in the surrounding index.