Abstract
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.
Highlights
Optical fibers are attractive candidates in sensing systems and offer many advantages over electrical and chemical sensors
For strain and structural deformation sensing, fiber Bragg gratings (FBGs) and long period fiber gratings (LPFGs) are popular choices owing to their simple structure, strong reflected signals, and potentially high sensitivity from a narrow spectral width [3,4]
Specialty fibers employing polygon-shaped cores [8,9], side-hole asymmetric fibers [10,11], and other novelty fibers [12] have been exploited to build vector sensors, allowing the detection of stress, strain or deformation associated with the specific radial direction
Summary
Optical fibers are attractive candidates in sensing systems and offer many advantages over electrical and chemical sensors. Specialty fibers employing polygon-shaped cores [8,9], side-hole asymmetric fibers [10,11], and other novelty fibers [12] have been exploited to build vector sensors, allowing the detection of stress, strain or deformation associated with the specific radial direction. Apart from their applications in safety monitoring, medical diagnosis and treatment, vector bend sensors may prove useful in telescope systems or other fine mechanics to track the angular position of the mirrors and to control the movement of the fiber-bundles.
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