OFDR-based shape sensor using a plane-by-plane-inscribed weak FBG array in multicore fiber.

An OFDR-based shape sensor was demonstrated using a weak fiber Bragg grating (WFBG) array inscribed in multicore fiber (MCF) by a femtosecond-laser plane-by-plane technique. An integrated modulation plane, consisting of a central square region and a concentric annular region, was introduced to simultaneously modulate multiple cores without precise core-by-core alignment. At a laser-focused scanning speed of 0.5 mm/s, one WFBG consisting of 10 integrated modulation planes could be fabricated within 35 s. After optimization of the inscription energy, grating order, and modulation plane number, a 60-cm-long WFBG array containing 60 gratings with a spacing of 1 cm was fabricated in the MCF and interrogated using OFDR. The fabricated sensor achieved relative reconstruction errors of 1.41% and 1.95% in 2D and 3D shape sensing, respectively.