Evanescent field FBG sensor with comb-like resonances

In the current research domain, the development of Fiber Bragg Grating (FBG) evanescent field sensors faces challenges of high manufacturing costs and poor repeatability. To solve this problem, we developed a novel FBG evanescent field sensor, which combines FBG with multi-mode fiber (MMF) to excite evanescent field through a simple fiber fusion technology, thus realizing a low-cost and high-resolution detection scheme. In a high reflectivity FBG, multiple cladding modes are excited when the forward guidance mode in the multimode fiber is coupled with the backward guidance mode of the FBG in the cladding. The evanescent field fiber sensor is highly sensitive to the surrounding refractive index without changing the fiber structure, and exhibits a full width half height (FWHM) of 78 pm and a quality factor (Q-factor) of 1.9×10⁴ at the standard cladding mode resonance, which is superior to most reported evanescent field fiber sensors on these parameters. The proposed fiber grating sensor significantly expands its application potential in the fields of biosensing and chemical analysis.