2D temperature sensing obtained by multiplexing of optical backscattering reflectometry

Distributed temperature sensing, achieved by Optical Backscattering Reflectometry (OBR), has potential in applications that require high sensitivity and resolution, such as thermal ablation. The working principle of OBR is based on monitoring the spectral signature of the light backscattered by the infinitesimal non-homogeneities inside the fiber, which changes as a result of strain or temperature variation. All the standard single-mode telecom optical fibers have almost the same scattering level, therefore, when multiple fibers are connected in parallel to the OBR, the instrument is unable to differentiate the pattern of each fiber. To overcome this issue, we proposed the use of fibers with different scattering level. Higher scattering can be achieved by creating a doping of MgO nanoparticles (size is 20-100 nm) in the fiber core, which results in roughly 50 dB increase of the scattering power. Several nanoparticles doped fibers (NPDF) have been spliced to standard single-mode fibers with variable lengths, in order to achieve spatial separation. The obtained fibers have been connected to the OBR by a 1x8 splitter. The backscattered spatial pattern consisted of several high-power regions separated by low-scattering zones given by fibers parallel. The proposed setup, applied in thermal ablation experiments, has shown that each sensing fiber is able to detect temperature variations distributed over the sensor length, and the scattering-level enabled multiplexing setup allows a detailed 2-dimensional temperature map. The resolution achieved in the pixel of the thermal map is in the order of millimeter. Moreover, the technique can be extended to obtain a 3D temperature map.