A Mach–Zehnder interferometer based on peanut structure for temperature and refractive index measurement

A fiber Mach–Zehnder (M-Z) interferometer based on the peanut structure is proposed to measure the temperature and the refractive index (RI). This design includes the peanut-like structure parts and a sensing part. The peanut structures are fused with single-mode fiber (SMF) and few-mode fiber (FMF). The middle sensing part is formed by cascading FMF and thin core fiber (TCF). We show that the light intensity ratio between the core and the cladding can be increased using additional FMF in the peanut structure and the middle sensing part. Moreover, the sensitivity of RI can be increased using the TCF in the sensing part. Experimental results show that the maximum RI sensitivity of the sensor is around 210 nm/RIU and the maximum temperature sensitivity reaches 310 pm/℃.