Compact Temperature Sensor With Highly Germania-Doped Fiber-Based Michelson Interferometer

A compact temperature sensor with highly germania-doped fiber (Ge-fiber)-based Michelson interferometer (MI) is proposed and experimentally demonstrated. It is constructed by splicing a 1-mm-long, 75 mol.% GeO 2 -doped fiber to a single-mode fiber and fabricating a taper at the splicing point. The fiber taper improves mode conversion efficiency and thus increases the extinction ratio of the interference fringe. The free spectral range is only 18.9 nm owing to the much larger differential refractive index of the Ge-fiber than normal fibers. By monitoring wavelength shift of the reflection spectrum, temperature measurement within a wide range of 30°C–400°C is successfully achieved with sensitivity up to 100 pm/°C, which is much higher than normal fiber-based MI sensors owing to the higher thermo-optic coefficient of the Ge-fiber. The compact size and high sensitivity make the proposed sensor a highly potential candidate in point measurement of temperature.