基于包层模的光纤布拉格光栅折射率传感特性

提出了基于光纤布拉格光栅(FBG)包层模式的折射率传感方案。实验中,利用不同浓度的丙三醇水溶液作为外界折射率传感溶液,采用氢氟酸溶液化学腐蚀的方法来减小光纤包层的直径以增大包层模式对外界折射率的敏感度,研究了腐蚀后光纤布拉格光栅包层模式的耦合波长对外部折射率的变化关系。实验结果表明在1.3300~1.4584的折射率范围内,包层模式耦合波长随外界折射率增大而增大,在接近光纤包层折射率处具有很高的折射率灵敏度,最大达到了172 nm/riu(refractive index unit)。而且,包层模谐振的光谱半峰全宽(约0.07 nm)仅为布拉格纤芯模谐振光谱半峰全宽的1/4,能够获得更好的传感精度。

Refractive Index Sensing Characteristics of Fiber Bragg Grating Based on Cladding Mode

A new refractive index sensing scheme based on the cladding modes of fiber Bragg grating (FBG) is presented. In the experiments, glycerin aquatic solutions with different concertrations are used as the external refractive index sensing media, and the cladding diameter of FBG is reduced by etching the fiber with HF solution to enhance the sensitivity of cladding modes to the external refractive index. Dependence of the coupling wavelength of the etched FBG cladding mode on the external refractive index is measured. The results show that in the refractive index range of 1.3300～1.4584, the coupling wavelength of cladding mode shifts longer with the increase of the external refractive index and a higher sensitivity is achieved when the external refractive index is close to that of fiber cladding's, and the maximum refractive index sensitivity reaches 172 nm/riu (refractive index unit). Furthermore, the full-width-at-half-maximum (FWHM) of resonant cladding mode is 0.07 nm, which is about 1/4 of that of the core mode's. With this narrower spectrum, a higher sensing resolution can be achieved.