Distributed shape sensing using Brillouin scattering in multi-core fibers

Abstract

A theoretical and experimental study on the response of Brillouin scattering in multi-core optical fibers (MCF) under different curving conditions is presented. Results demonstrate that the Brillouin frequency shift of the off-center cores in MCF is highly bending-dependent, showing a linear dependence on the fiber curvature. This feature is here exploited to develop a new kind of distributed optical fiber sensor, which provides measurements of a distributed profile mapping the longitudinal fiber shape. Using conventional Brillouin optical time-domain analysis with differential pulse-width pairs, fully distributed shape sensing along a 1 km-long MCF is practically demonstrated. Experimental results show a very good agreement with the theoretically expected behavior deduced from the dependence of the Brillouin frequency on the strain induced by the fiber bending over a given core. The analysis and results presented in this paper constitute the first demonstration of distributed bending sensing, providing the cornerstone to further develop it into a fully distributed three-dimensional shape sensor.

A Brief Review of Specialty Optical Fibers for Brillouin-Scattering-Based Distributed Sensors

“…They suggested that the change in coefficients largely can be attributed to practical differences in the core materials. Zhao et al [125,126] showed that the Brillouin scattering response of multi-core fibers is highly sensitive to bending, thus paving the way for three-dimensional shape sensors.…”

Brillouin scattering effect in the multicore optical fiber applied to fiber optic shape sensing

“…µm In distributed measurements based on the Brillouin scattering effect, backcoupled light with shifted frequency is observed. This frequency shift, called Brillouin Frequency Shift (BFS), is a value which is constant in unchanged external conditions for a given fiber and is defined as 1,2 where is the effective refractive index, is the acoustic wave velocity and is the incident wavelength.…”

“…Hence, the BFS can be expressed using the mentioned relation for strain where is a variation of the BFS in the i-th core and is an initial BFS value in reference conditions (in the case of the MCF7 the BFS for central core can be used). Based on this relation and acquiring BFS measurements for at least 3 lateral cores, it is possible to determine the bend radius and orientation at each point along the fiber in the 3D space 1,17 .…”

“…Additionally, multicore fibers are suitable for inscription of fiber Bragg gratings (FBG) 9 , which can be useful for shape sensing 10,11 . Recently, observations of Brillouin scattering effect in multicore fibers were reported 12 and the effect was successfully applied for shape sensing 1 . Unlike in previous report 1 , here authors used multicore fiber with air-hole isolation.…”

“…Recently, observations of Brillouin scattering effect in multicore fibers were reported 12 and the effect was successfully applied for shape sensing 1 . Unlike in previous report 1 , here authors used multicore fiber with air-hole isolation.…”