光纤Bragg光栅对外界折射率的变化不灵敏,无法直接作为气体、液体等的敏感元件.侧面研磨的光纤Bragg光栅,一侧包层减小至几微米,其辐射场可通过包层透射到被传感物质,因而被传感物质的折射率的变化可以改变光纤的有效折射率,从而使光栅的Bragg波长产生位移.实验中利用不同浓度的NaCl溶液来改变光纤光栅的外部折射率,Bragg中心波长的偏移量和浓度近似为线性关系.同时,透射功率的变化量和浓度也近似为线性关系.

Fiber Bragg grating (FBG) cannot be directly used as gas or liquids sensors, because it is not sensitive to external refractive index.By side-polished,the cladding layer of one side of FBG can be reduced to several micrometers.The radiation field can reach the external medium.When the external refractive index changes, the effective refractive index of fiber changes and the center wavelength of D-shaped FBG shifts accordingly.In the experiment,the NaCl solution with different concentration is used to change the external refractive index of FBG.The center wavelength of D-shaped FBG shifts when the concentration of NaCl solution changes.The relationship between the offset of wavelength and the concentration of NaCl solution is approximately linear.In addition,the relationship between the transmitting power and the concentration of NaCl solution is also approximately linear.