Enhanced Sensitivity of Nitrite Detection Using a Fabry-Perot Cavity Based on C-Type Fiber

In this paper, a Fabry-Perot cavity based on a C-type fiber is designed, in which a resonant cavity consists of fusion splicing the two ends of the C-type fiber with a single-mode fiber. The resonant cavity is fixed in a glass tube with a diameter of 0.8 cm and a length of 2 cm, and then a capillary tube with a diameter of 0.4 cm is inserted into both ends of the glass tube, which can be encapsulated to obtain a sensing structure that meets the liquid input and output. We used this sensing structure for the detection of nitrite concentration and compared it with that without the sensing structure. The experimental results showed that the sensitivity of nitrite detection could be improved by about 14.5 times by utilizing the resonant cavity. The sensor designed in this paper has a simple structure, is easy to fabricate, and can enhance the sensitivity of fluorescence detection; therefore, it can be generalized to other sensors based on fluorescence detection.