C+L 波段低弯曲损耗非耦合三模组渐变折射率光纤设计

Optical fiber is the most stable medium for signal transmission in modern communication networks. Increasing the number of fiber modes is an effective way to meet the increasing demand for communication capacity. In this paper, a kind of uncoupled three-mode-group (LP₀₁, LP₁₁, LP₂₁) graded-index fiber with low bending loss is designed. The strict cut-off conditions of the mode groups in the graded-index optical fiber are obtained by using the stratified method. In addition, the effective mode area and bending losses are calculated by a finite element simulation software, and the design region of three-mode-group transmission in the C+L (1 530~1 625 nm) band with low bending loss is obtained. It is revealed that the combined effects of the concave refractive index at the core center and the trench layer can promote the cutoff of radial higher-order modes in the fiber. The simulation results show that the designed fiber has a large effective index difference between mode groups that is ≥ 3×10^-3, and the maximum bending loss is 1.3 dB/km when the bending radius is 30 mm, which meets the low bending loss condition recommended by ITU-T. In addition, at the wavelength of 1 550 nm, the degenerate modes in the same mode group have a relatively small differential mode group delay (≈176 ps/km), and the crosstalk between degenerate modes can be compensated by 4×4 multi-input multi-output technique. This fiber can be used in the C+L band to realize uncoupled space-division multiplexing signal transmission.