Simultaneous Measurement of Refractive Index and Temperature Based on a Peanut-Shape Structure In-Line Fiber Mach–Zehnder Interferometer

We proposed a peanut-shape structure in-line fiber Mach-Zehnder interferometer (MZI) for simultaneous measurement of refractive index (RI) and temperature. Two kinds of demodulation methods were investigated and compared. The wavelength-related and phase-related character matrices of the in-line fiber MZI were determined for simultaneous measurement of RI and temperature, respectively. For the wavelength-related measurement, the highest temperature and RI sensitivities were 0.0709 nm/°C and -47.3620 nm/RIU, respectively. The phase-related measurement was with a lower measuring errors compared to the wavelength-related measurement, and the highest temperature and RI sensitivities were -0.0632rad/°C (0.0764 nm/°C) and 77.0995rad/RIU (-93.2429 nm/RIU), respectively. The minimum measuring errors of temperature and RI were 0.3800 °C and 0.0004 RIU, respectively.