Influence of high temperatures on a fiber-optic probe for temperature measurement

Multicore fiber sensor for high-temperature applications up to 1000°C

A novel high temperature sensor based on customized multicore fiber (MCF) is proposed and experimentally demonstrated. The sensor consists of a short, few-centimeter-long segment of MCF spliced between two standard single-mode fibers. Due to interference effects, the transmission spectrum through this fiber chain features sharp and deep notches. Exposing the MCF segment to increasing temperatures of up to 1000°C results in a shift of the transmission notches toward longer wavelengths with a slope of approximately 29  pm/°C at lower temperatures and 52  pm/°C at higher temperatures, enabling temperature measurements with high sensitivity and accuracy. Due to its compact size and mechanical rigidity, the MCF sensor can be subjected to harsh environments. The fabrication of the MCF sensor is straightforward and reproducible, making it an inexpensive fiber device.

High-temperature effects in fluorine-doped, fused synthetic silica fibers

Effects caused by exposure of large-core, fluorine-doped, step-index silica optical fibers to high temperatures were studied experimentally in controlled laboratory conditions. A fiber was located partially inside a temperature-controlled electric tube furnace and irradiated from the end by a light source. The light source was either an incandescent halogen lamp or a blackbody radiator. The influence of fiber temperature on the angular distribution of the radiation in the fiber and the coupling and propagation of thermal radiation in the fiber was studied. With increasing temperature the profile of the angular distribution of the radiation was transformed irreversibly from a Chinese hat profile to a much flatter one. This effect was pronounced at 1000 degrees C and above. Radiation from the furnace was found to propagate in the fiber as an attenuating mode at temperatures above 800 degrees C. Most of the radiation exited the fiber at angles beyond but close to the acceptance angle. Calculations show that thermal self-radiation of the fiber is negligible. The physical explanations for these effects are discussed and practical conclusions are drawn.