Refractive index Mach–Zehnder interferometer sensor based on tapered no-core fiber

A Mach–Zehnder interferometer sensor based on tapered no-core fiber (NCF) is proposed in this paper. Due to the multimode interference of the single-mode fiber (SMF)–NCF–SMF structure and the higher-order modes excited by the tapered structure, the sensor is more sensitive to the refractive index. The refractive index sensitivities are 130.5 nm RIU −1 from 1.340 to 1.380, 330.0 nm RIU −1 from 1.380 to 1.420, and 906.0 nm RIU −1 from 1.420 to 1.440, respectively. The temperature sensitivity is 0.0595 nm °C −1 from 30 °C to 90 °C. This proposed sensor has a simple structure and low cost, which can be widely used for biological sensing.