Reflected power-based 2D bending sensor using femtosecond laser FBG inscription in multicore fiber

In this paper, we present research on the use of femtosecond lasers to develop a two-dimensional bending sensor by inscribing a 4 mm fiber Bragg grating (FBG) in each of the four cores of a multicore fiber (MCF) Fibercore SM-4C1500. The sensor located at the end of the fiber is spliced to a 50/125 multimode fiber (MMF). Due to the geometry of the MCF, part of its cores do not directly attach to the core of the multimode fiber, so that different curvatures cause variations in the reflected power. In this way, a reflection configuration and a commercial spectrometer are used to study its power response, simplifying the sensing, since it is not necessary to have WDM elements for the handling of wavelengths that vary tenths of nm in this type of sensors. Likewise, by carefully controlling the laser parameters and the motor stage position we are able to inscribe the FBGs by means of the point-by-point (PbP) method.