Light–matter interaction at dielectric interfaces usually manifests as spin-dependent correction to light propagation, known as classical Imbert–Fedorov (IF) shift or photonic spin Hall effect, ruled by the general spin–orbit interaction (SOI) of light. Even though vector wave equations and strong SOI-based perturbation theory in a wave picture can offer good solutions to describe the modal dispersion in optical fibers, it is difficult for all these to provide an intuitive insight into the walking off for twisted (or vortex) light beams carrying orbital angular momentum (OAM). Here we present a new perspective to the topologically spin-dependent modal splitting for the twisted light highly confined in optical fibers based on the classical IF shift on geometric optics. We verify this topologically IF-shift-based walking off by comparing the analytical results of modal splitting degrees with the solutions of eigen equation, and associate the longitudinal projection of IF shift with an interesting resonance of fiber Bragg gratings locked by the signs of SAM or OAM. This interpretation provides an insight supplement to describe light ray propagating in optical fibers together with both longitudinal Goos–Hnchen and transverse IF shift under the total internal reflection, and may benefit the development of nanoscale fiber-based light on optically classical or quantum communication and metrology.

介电界面处的光-物质相互作用通常表现为对光传播的自旋相关校正，称为经典的 Imbert-Fedorov (IF) 位移或光子自旋霍尔效应，由光的一般自旋轨道相互作用 (SOI) 控制。尽管矢量波动方程和波图中基于 SOI 的强微扰理论可以提供很好的解决方案来描述光纤中的模态色散，但所有这些都很难提供对扭曲（或涡流）走离的直观洞察携带轨道角动量 (OAM) 的光束。在这里，我们基于几何光学上的经典 IF 位移，为高度限制在光纤中的扭曲光的拓扑自旋相关模态分裂提出了新的视角。我们通过将模态分裂度的分析结果与本征方程的解进行比较来验证这种基于拓扑中频偏移的走离，并将中频偏移的纵向投影与由 SAM 或 SAM 符号锁定的光纤布拉格光栅的有趣共振相关联。运维。这种解释为描述光纤中传播的光线以及全内反射下的纵向 Goos-Hnchen 和横向 IF 偏移提供了深入的补充，并且可能有利于基于纳米级光纤的光在光学经典或量子通信和计量学方面的发展.