Vector bending sensor based on low-cost single-channel measurement and highly reliable three-peak reconstruction algorithm

A vector bending sensor based on low-cost single-channel measurement and a highly reliable three-peak reconstruction algorithm is proposed. The sensor consists of single-mode fiber (SMF), multimode fiber (MMF) and two side-hole fibers (SHFs) of different lengths, with a 90° offset angle. The lengths of MMF and SHFs are 375 μm, 400 μm and 300 μm. Fresnel reflection occurs at the interface due to the difference in refractive index (RI) between air and fiber cladding, creating three reflective surfaces. Three Fabry-Perot interferometers (FPIs) with different optical path difference (OPD) are constructed using only two SHFs. A low-cost single-channel measurement method is employed to simultaneously demodulate the interference signals from the three FPIs. When bending is applied to the sensor, each FPI exhibits different strain variation. Experimental results show that the bending responses of FPIs are highly dependent on the bending directions, and each of them exhibits its maximum sensitivity at a different bending direction. The maximum positive sensitivities of FPIs are 155.11 pm/m-1 (0°), 210.45 pm/m-1 (225°), and 91.78 pm/m-1 (255°), respectively. Thus, the three FPIs are located at different spatial positions, making them fitted for vector bending sensing. In addition, the application of the three-peak reconstruction algorithm significantly enhances the stability and reliability of the curvature and bending direction reconstruction.