Abstract
In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal. The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end. The two groups of cladding mode resonances in the reflection spectrum respond differentially to bending, which allows for the unique determination of the magnitude and orientation of the bend plane (i.e. with a ± 180 degree uncertainty). Bending responses ranging from −0.33 to + 0.21 dB/m−1 (depending on orientation) are experimentally demonstrated with bending from 0 to 3.03 m−1. In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.
Highlights
Fiber Bragg grating (FBG) based sensors have been widely used for static/dynamic structural deformation in various engineering applications including oil well exploration, pipeline monitoring and maintaining and structural health monitoring[1]
A similar structure with a serial arrangement of tilted fiber Bragg gratings (TFBGs) oriented along different tilt planes has been demonstrated earlier for the purpose of polarization-resolved monitoring of the power carried by optical fibers in telecommunication systems[19]
We used two TFBGs with a tilt angle φ of 2 degree connected in series with their tilt orientation at ~90 degrees from each other, a followed by a cleaved end face acting as a mirror
Summary
Fiber Bragg grating (FBG) based sensors have been widely used for static/dynamic structural deformation in various engineering applications including oil well exploration, pipeline monitoring and maintaining and structural health monitoring[1]. Because of the additional mechanical transducing methods required, these sensors tend to occupy relatively large volumes and to require relatively complex assembly that are difficult to make resistant to damage To avoid these problems, it has recently been demonstrated that 3D shape sensing could be realized with series of FBGs embedded off axis along different directions inside optical fibers[10,11]. It will be shown experimentally that this simple structure allows the measurement of the magnitude and direction of relatively small curvatures between 0 and 3 m−1, as well as the determination of the strain along the fiber axis, completing the requirement for a full 3D shape sensor These results are explained by the fact that the coupling to certain cladding modes increases for bending along the tilt plane but decreases for bending in the orthogonal direction[20]. To conventional FBG strain gauges, this 3D shape sensing device can be embedded into structures and laminates for robustness
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