A Dual-Wavelength Scheme for Brillouin Temperature Sensing in Optically Heated Co 2+ -Doped Fibers

In this paper, we propose the use of a dual wavelength scheme for active distributed temperature sensing based on Co ²⁺ -doped fibers. A Brillouin Optical Frequency-Domain Analysis (BOFDA) set-up, operating at 850 nm, is used to detect the temperature changes along Co ²⁺ -doped optical fibers with various absorption coefficients, while optical heating is performed through a 1550-nm optical pump. A simple model describing optical heating along the Co ²⁺ -doped fiber is introduced and experimentally validated. As a proof of concept, we demonstrate that the sensor is capable to distinguish a 1-m portion of fiber immersed into water, from a section of equal length surrounded by air.