Simulation and experimental verification of off-axis fiber Bragg grating bending sensor with high refractive index modulation

Abstract

Off-axis FBG simulations were performed in this paper using a finite element method in conjunction with the conformal mapping technique to study the bending sensing characteristics of the off-axis FBG with high index modulation. The refractive index (RI) increase of the grating region is taken into consideration for the mode field simulation. The influences of high RI increase and the offset distance of the grating on the bending sensitivity were analyzed. Off-axis FBGs with different offset distances were fabricated using femtosecond laser with phase mask technique in standard single-mode fiber. The simulation results were verified by the experiment. A bending sensitivity of 0.055 dB/m⁻¹ was achieved with an offset distance of 4 μm. The simulation and experiment results suggest that the grating offset distance has a greater influence on the sensitivity of the off-axis FBG with high RI modulation than that with low RI modulation. The proposed sensor structure and simulation results can provide suggestion for the design and processing of off-axis FBG bending sensors.

References

[1] KumariC U, SamiappanD, KumarR, et al.. Fiber optic sensors in ocean observation: a comprehensive review[J]. Optik, 2019, 179: 351-360

[2] LiangQ, ZouK, LongJ, et al.. Multi-component FBG-based force sensing systems by comparison with other sensing technologies: a review[J]. IEEE sensors journal, 2018, 18(18):7345-7357

[3] ZhuH H, ShiB, ZhangC C. FBG-based monitoring of geohazards: current status and trends[J]. Sensors, 2017, 17(3):452

[4] GuoT, ShaoL, TamH Y, et al.. Tilted fiber grating accelerometer incorporating an abrupt biconical taper for cladding to core recoupling[J]. Optics express, 2009, 17(23): 20651-20660

[5] YakushinS S, WolfA A, DostovalovA V, et al.. A study of bending effect on the femtosecond-pulse inscribed fiber Bragg gratings in a dual-core fiber[J]. Optical fiber technology, 2018, 43: 101-105

[6] TianK, FarrellG, YangW, et al.. Simultaneous measurement of displacement and temperature based on a balloon-shaped bent SMF structure incorporating an LPG[J]. Journal of lightwave technology, 2018, 36(20):4960-4966

[7] FengD, QiaoX, AlbertJ. Off-axis ultraviolet-written fiber Bragg gratings for directional bending measurements[J]. Optics letters, 2016, 41(6):1201-1204

[8] WaltermannC, BethmannK, DoeringA, et al.. Multiple off-axis fiber Bragg gratings for 3D shape sensing[J]. Applied optics, 2018, 57(28):8125-8133

[9] ChenF, SuD, QiaoX, et al.. Compact vector bend sensor using dual-off-axis innermost cladding-type FBGs[J]. IEEE sensors journal, 2018, 18(18):7476-7480

[10] CusanoA, ConsalesM, CrescitelliA, et al.. Lab-on-fiber technology[M], 2015, 1st ed.Switzerland, Springer International Publishing

[11] SmelserC W, MihailovS J, GrobnicD. Formation of Type I-IR and Type II-IR gratings with an ultrafast IR laser and a phase mask[J]. Optics express, 2005, 13(14):5377-5386

[12] MihailovS J, GrobnicD, SmelserC W, et al.. Bragg grating inscription in various optical fibers with femtosecond infrared lasers and a phase mask[J]. Optical materials express, 2011, 1(4):754-765

[13] DavisK M, MiuraK, SugimotoN, et al.. Writing waveguides in glass with a femtosecond laser[J]. Optics letters, 1996, 21(21):1729-1731

[14] RennerH. Bending losses of coated single-mode fibers: a simple approach[J]. Journal of lightwave technology, 1992, 10(5):544-551

[15] SchermerR T, ColeJ H. Improved bend loss formula verified for optical fiber by simulation and experiment[J]. IEEE journal of quantum electronics, 2007, 43(10):899-909