Fiber In-Line Mach–Zehnder Interferometer Embedded in FBG for Simultaneous Refractive Index and Temperature Measurement

An ultracompact optical fiber sensor based on a Mach-Zehnder interferometer (MZI) embedded in fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement. By use of the resonant wavelength of the FBG and the interference dip of the MZI, the RI and temperature of the surrounding medium can be unambiguously determined. The interesting properties of the sensor include good operation linearity, extremely high RI sensitivity up to ~ -9148 nm/RI unit in the RI range between 1.30 and 1.325, and precise sensing location, determined by the MZI cavity created.