Pure Directional Bending Measurement With a Fiber Bragg Grating at the Connection Joint of Eccentric-Core and Single-Mode Fibers

Abstract

A novel fiber Bragg grating (FBG) structure based on an eccentric core fiber (ECF) and a single-mode fiber (SMF) was proposed and experimentally demonstrated for distinguishing the bending effect from the axial strain effect and measuring the pure directional bending. The structure is fabricated by writing a FBG on the fusion splice junction between an ECF and a SMF. The FBG formed on the ECF-SMF junction has two different resonant peaks because of the different refractive indices of the two fibers. The peak relating to the ECF is sensitive to both directional bending and axial strain, while the peak corresponding to the SMF is only sensitive to strain. By using the unique FBG structure, one can directly know whether a bending is accompanied by an axial strain, and can obtain both the direction and curvature of the bending. Experimental results show that the bending sensitivities of the FBG in the ECF part are 49.3 pm/m -1 and -50.3 pm/m -1 at directions of 0° and 180°, respectively, and the strain sensitivities of the FBG in the ECF and SMF are 0.74 pm/με and 0.70 pm/με, respectively.

Multifunctional Textile Platform for Fiber Optic Wearable Temperature-Monitoring Application

“…Osorio et al explored the bending impact on a surface-core fiber and observed a directional behavior of the optical response in the curvature probing due to the fiber geometry [42]. When the core lay on the center axis, as represented in the results of the study of Kong et al, no obvious wavelength shift was observed in the test, which was confirmed by our curvature testing results [40]. This finding can be explained by the circularly symmetrical structure of the single-mode fiber, in that bending applied on any direction of the fiber will not cause much extension or compression to the core.…”

“…When the FBG core region was out of the center of symmetry, the working area was likely to experience extension or compression during bending, leading to a wavelength shift. Kong et al conducted a bending experiment on FBG at the connection joint of eccentric-core and single-mode fibers with the results of redshift and blueshift representing near-linear features [40]. Chen et al studied the bending impact on the Bragg grating written in an eccentric-cored polymer optical fiber, with the results indicating a strong orientational dependence and high bend sensitivity [41].…”

In-Line Mach-Zehnder Interferometer With D-Shaped Fiber Grating for Temperature-Discriminated Directional Curvature Measurement

“…Thus, the MZI can be used directional bending sensing. For the FBG inscribed in the D-shaped fiber, the resonant wavelength, given by G=2neff, will also shift due to the bending, following [3]  …”

“…fiber grating-based [1][2][3][4][5][6][7][8][9], interferometer-based schemes [10][11][12][13][14][15][16][17][18], etc. For fiber grating-based structures, such as fiber Bragg gratings (FBGs) written in multi-core fiber (MCF) and eccentric-core fiber (ECF) [3,4], long-period fiber gratings (LPFGs) [5][6][7] and tilted FBGs [8,9], they can operate in a large curvature range, but exhibit a lower sensitivity. For in-line interferometer-based curvature sensors, Mach-Zehnder interferometers (MZI) as a common and effective scheme usually involves two fiber mode-coupling joints, where the two joints act as a beam splitter and a beam combiner.…”

Novel Fiber Grating for Sensing Applications

“…The LPFGs inscribed by various technologies have different features, which have attracted more and more researchers to study on them. In addition, Guan et al utilized a superstructure FBG to achieve the simultaneous measurement of strain and temperature; Kong et al proposed a pure directional curvature sensor by inscribing an FBG on the fusion splice junction between an eccentric core fiber (ECF) and an SMF; Wang et al put forward a micro‐displacement sensor with enhanced sensitivity via the slow light in the FBG; Chen et al combined a micro extrinsic Fabry–Perot interferometer with an etched FBG for the simultaneous measurement of strain and magnetic field. Additionally, the FBG could also be used as a tool of the peak tracking method because of its narrow‐band spectrum.…”