Hollow-Core-Fiber-Based Interferometer for High-Temperature Measurements

We report a new fiber optic sensor for temperature measurement at a temperature range of up to 900  °C with excellent stability and repeatability. The sensing head is comprised of a short hollow-core fiber segment spliced between two single-mode fibers using a commercial splicer. Optical power from the lead-in fiber is partly coupled to silica cladding of the hollow-core fiber with the remainder propagating in air core by short distance. The two beams are then re-coupled to the core of the lead-out fiber, owing to the offset splicing joint. Due to the effective index difference between the two beams, an interference pattern in the transmission spectrum is obtained. The distinct thermo-optic coefficients between silica and air result in a high-temperature sensitivity of 41 pm/ °C, and the enclosed structure ensures its immunity to the external refractive index.