A novel birefringent fused cone Sagnac ring refractive index sensor

A novel birefringent fused-cone coupling Sagnac-interference refractive index sensor is proposed in this study. First, single-mode optical fiber is fused with photonic crystal fiber (PCF) to form SMF - PCF - SMF interference. Second, the single-mode optical fiber at both ends of the PCF is folded in half to form a ring and placed on the translation stage of optical fiber for taper coupling to form a Sagnac interferometer connection for PCF. Finally, strong evanescent field characteristics of fiber coupling and the presence of birefringence in the coupling region are used and the prepared sensor is placed in a solution with different refractive indices. Experimental results showed that sensitivity reaches 186.656 nm/RIU in the refractive index range of 1.339 – 1.367. The sensor structure with high sensitivity, simple manufacture, and low cost plays an important role in food safety and chemical industry.