Thin-Core Fiber Sandwiched Photonic Crystal Fiber Modal Interferometer for Temperature and Refractive Index Sensing

A photonic crystal fiber modal interferometer (PCFMI) with two segments of thin-core fiber functioning as a mode exciter and a re-coupler was proposed, analyzed, and experimentally demonstrated for temperature and refractive index (RI) sensing. Theoretical analysis and simulations were first conducted, to investigate the mode propagating behavior and the phase matching condition. Experimental results showed that RI sensitivity of 48.9 nm/RIU within the range of 1.34 ~ 1.40, and temperature sensitivity of 1.7 pm/°C can be obtained, which are comparable to those of the normal PCFMI structure. The liquid with RI of 1.40 was filled into the PCF to further improve the sensing performance. The RI and temperature sensitivities were enhanced to 283.9 nm/RIU and -354.1 pm/°C, respectively. Such good performance renders our proposed structure a promising platform for refractive index and temperature sensing applications, with the features of high sensitivity, compact size, easy fabrication, and low cost.