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    Fiber Vector Bend Sensor Based on Multimode Interference and Image Tapping
    (Basel : MDPI, 2019) Zhang, Ziyang; Rahman, Aashia; Fiebrandt, Julia; Wang, Yu; Sun, Kai; Luo, Jiajun; Madhav, Kalaga; Roth, Martin M.
    A grating-less fiber vector bend sensor is demonstrated using a standard single mode fiber spliced to a multimode fiber as a multimode interference device. The ring-shaped light intensity distribution at the end of the multimode fiber is subject to a vector transition in response to the fiber bend. Instead of comprehensive imaging processing for the analysis, the image can be tapped out by a seven-core fiber spliced to the other end of the multimode fiber. The seven-core fiber is further guided to seven single mode fibers via a commercial fan-out device. By comparing the relative light intensities received at the seven outputs, both the bend radius and its direction can be determined. Experiment has shown that a slight bend displacement of 10 µm over a 1.2-cm-long multimode fiber in the X direction (bend angle of 0.382 ◦ ) causes a distinctive power imbalance of 4.6 dB between two chosen outputs (numbered C4 and C7). For the same displacement in the Y direction, the power ratio between the previous two outputs C4 and C7 remains constant, while the imbalance between another pair (C3 and C4) rises significantly to 7.0 dB. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.