Double-core fiber contains two cores in the same cladding, each core is an optical waveguide, that is, two single-core fibers are integrated in a double-core fiber. Double-core optical fiber has various structures

Study on mode field characteristics of dual-core fiber

The transmission characteristics of single-mode fiber are determined by the parameters of cladding refractive index, core refractive index, core radius and transmission wavelength. For dual-core fiber, the transmission characteristics of the fiber are also related to the distance between the two cores. Changing the distance between the two cores of a dual-core fiber will affect the energy distribution between the two cores. During the simulation process, it is always ensured that one core is at the same position of the central axis of the cladding, and the distance d between the two cores is changed by changing the position of the side core

Birefringence of dual-core fiber

General axisymmetric single-mode fiber can simultaneously transmit two linear polarization orthogonal modes or two circular polarization orthogonal modes. In an ideal case, if the optical fiber has complete circular symmetry, the two orthogonal modes have the same propagation constant in the optical fiber. They are parallel to each other, and the polarization state will not change during the propagation. But in fact, because of the internal stress, external pressure, and the roundness of the fiber itself, the refractive index deviation under these two polarization modes will result in different propagation constants. Due to the different propagation speed of the two orthogonal polarization modes, the two orthogonal modes will be combined in the transmission process, and the resultant polarization state will change in the transmission process, which is the birefringence effect of the fiber. The waveguide structure of dual-core fiber does not have circular symmetry, so its birefringence should be analyzed. The birefringence of dual-core fiber can be simulated and calculated by APSS software. According to the measured data, the simulation parameters are set as follows: the diameter of cladding is 125 μ m. Core diameter is 9 μ m. The core spacing is 43 μ m. The refractive index of cladding and fiber core is 0.36% doped with silica and relative cladding refractive index respectively

Optical fiber devices based on dual-core optical fiber have the advantages of easy accurate control of device size, small mechanical stress in the coupling area, more compact and stable, and not easy to be affected by the outside world. They have been widely used in optical sensing and optical communication and other fields, mainly reflected in optical fiber filters, optical interferometers, optical connectors, optical fiber amplifiers, optical add-in multiplexers, optical fiber switches, optical tweezers and optical fiber sensors. Therefore, the research of dual-core fiber has important theoretical and practical significance. With the deepening of the research, it will bring new breakthroughs to optical fiber communication and optical fiber sensing