Multiplexing of distributed temperature sensing achieved by nanoparticles doped fibers

Distributed sensing based on Optical Backscattering Reflectometry (OBR) is a promising solution for medical applications, such as thermal ablation. OBR working principle is based on the change in pattern of small reflections from non-homogeneities inside the fiber as a response to applied strain and temperature. The advantage of OBR is its high resolution and sensitivity. However, since the scattering level is the same for standard single-mode fibers, OBR is unable to discriminate the pattern of different fibers when they are connected in parallel to a single channel. As a result, OBR detection is limited to a single sensing fiber and does not allow multiplexing. This work proposed a method to overcome the aforementioned limitation by the use of high-scattering fibers. Such fibers are achieved by doping their core with magnesium oxide particles, which size varies from 20 to 100 nm. The backscattering level of nanoparticles doped fiber (NPDF) is 50 dB higher than of the standard fibers. Four NPDFs have been spliced to the standard single-mode pigtails with different length to achieve four sensing regions located at different distances from pigtails. The NPDF sensors have been connected to the OBR equipment by the use of optical couplers and the backscattered pattern has shown four high-scattered sensing regions separated by low-scattering regions from standard fibers. The proposed setup has been applied in the thermal ablation experiments and the 2-dimensional map of temperature change with time has been obtained.