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.