Research on High Sensitive Refractive Index Sensor Based on D-Single Mode Fiber

A Mach-Zehnder interferometer (MZI) sensor with a D-single mode fiber (DSMF) cascaded peanut-shaped structure that can measure refractive index (RI) is designed. In this structure, the peanut-shaped is used as an input/output coupler, and the DSMF is used as the sensing area. The sensor characteristics are enhanced by polishing the SMF in the middle. Two peanut-shaped structures are added to the spindle structure, which is more favorable to excite the higher-order cladding modes to generate more modal interference. The deeper the polishing depth, the better the sensitivity. When the polishing depth is 47.1mm with the RI concentration changes from 1.390 to 1.440, the RI sensitivity is 785.53nm/RIU. In addition, the temperature characteristics are studied. In the range of 30°C~80°C, the temperature sensitivity is 0.048nm/°C. This structure is more sensitive to high concentrations RI. This structure has the advantages of small volume, good repeatability, and high sensitivity.