Recirculation method for temperature measurement by the fiber optical sensor

A new principle of physical quantities measurement is described, based on recording changes in the frequency of single optical pulses recirculation at different wavelengths in a closed fiber optic loop with their periodic regeneration in amplitude, shape and duration. It was established that the relative long-term instability of the recirculation frequency does not exceed $2\cdot10^{-6}$ for fibers longer than $200$ m with a measurement time of $1$ s and an observation time more than $1$ hour. Using numerical simulations, it was shown that the resolution of the temperature sensor is $0.15$–$0.1^\circ$ C in the temperature range $0$–$500^\circ$ C using quartz fiber with a metallic coating.