A C-OTDR Sensor for Liquid Detection Based on Optically Heated Co2+-Doped Fibers

In this paper, we propose a dual wavelength scheme for the detection of liquids based on optically absorbing (Co
²⁺
-doped) optical fibers. The proposed configuration makes use of a Coherent-Optical Time Domain Reflectometer (C-OTDR) operating with standard fibers at 850 nm. Besides vibration measurements over all the sensing fiber, the proposed scheme performs liquid detection in short sections of Co
²⁺
-doped fibers, heated by a modulated optical pump at 1550 nm. We demonstrate that the proposed sensor detects the liquids surrounding the doped fiber, such as water or acetone.