Bending Sensor Based On Hole Assisted Three Core Fiber Coupling

Multicore optical fibers,with their unique space division multiplexing performance,have gained enormous advantages in fiber optic sensing,especially in fiber optic bending sensing.Multicore optical fibers achieve effective and accurate curvature sensing and direction recognition by sensing the differential response generated by fiber optic bending changes through multiple fiber cores.To date,many bending sensors based on multi-core optical fibers have been reported and widely used in bridges,medical monitoring,and industrial manufacturing In various fields such as device sensing.In this paper,a hole assisted three core optical fiber is designed,which includes a central core and two suspension cores with different diameters.With the assistance of air holes,the central core can realize mode coupling with the two suspension cores at different wavelengths.The dispersion and transmission characteristics of the hole assisted three core optical fiber are simulated and analyzed,and a bending sensor is made based on its coupling performance,which is of great significance to improve the optical fiber bending sensing technology.The main works of this thesis are listed as follows:（1）Simulate and analyze the dispersion and transmission characteristics of the core mode of the hole assisted three core fiber.Through finite element simulation,the influence of the suspended core diameter and the refractive index difference of the core cladding on the fundamental mode dispersion of the three cores of the hole assisted three core fiber is explored,and the design parameters of the hole assisted three core fiber are determined.According to the design parameters,the hole assisted three core fiber is drawn,and the optimal mode coupling between the central core and the two suspended cores is obtained at1365 nm and 1604 nm,respectively.According to the finite difference beam method,the corresponding optical fiber transmission lengths at the two coupling wavelengths are 19.9 mm and 9.8 mm,respectively..（2）The production and testing of a bending sensor based on hole assisted three core fiber coupling.Gradually cut the hole to assist in determining the length of the three core optical fiber.The actual coupling lengths between the center core and the two suspension cores are 19mm and 7 mm,respectively,with corresponding coupling wavelengths of 1369.2 nm and1607.4 nm.Select a hole assisted three core fiber with two optimal coupling peaks at a length of 11 mm and fusing it with a single mode fiber to make a sensor,a curvature of 0.5477～2.0494 m^-1 is applied to the sensor in eight directions at intervals of 45°from 0°to 315°.The experiment shows that the sensor can achieve a maximum curvature sensitivity of 50.62 nm/m^-1 in the 0°direction and can effectively identify eight bending directions.In addition,The sensor has a maximum temperature sensitivity of-34.9 pm/°C in the temperature range of 20～75°C.