Nonreciprocal light propagation induced by a subwavelength spinning cylinder

Nonreciprocal optical devices have broad applications in light manipulations for communications and sensing. Non-magnetic mechanisms of optical nonreciprocity are highly desired for high-frequency on-chip applications. Here, we investigate the nonreciprocal properties of light propagation in a dielectric waveguide induced by a subwavelength spinning cylinder. We find that the chiral modes of the cylinder can give rise to unidirectional coupling with the waveguide via the transverse spin-orbit interaction, leading to different transmissions for guided wave propagating in opposite directions and thus optical isolation. We reveal the dependence of the nonreciprocal properties on various system parameters including mode order, spinning speed, and coupling distance. The results show that higher-order chiral modes and larger spinning speed generally give rise to stronger nonreciprocity, and there exists an optimal cylinder-waveguide coupling distance where the optical isolation reaches the maximum. Our work contributes to the understanding of nonreciprocity in subwavelength moving structures and can find applications in integrated photonic circuits, topological photonics, and novel metasurfaces.

非互易光学器件在通信和传感的光操控方面具有广泛应用。对于高频片上应用，非常需要光学非互易性的非磁性机制。在此，我们研究了由亚波长旋转圆柱在介质波导中引起的光传播的非互易特性。我们发现，圆柱的手性模式可通过横向自旋 - 轨道相互作用与波导产生单向耦合，导致在相反方向传播的导波具有不同的透射率，从而实现光隔离。我们揭示了非互易特性对各种系统参数的依赖性，包括模式阶数、旋转速度和耦合距离。结果表明，高阶手性模式和较大的旋转速度通常会产生更强的非互易性，并且存在一个使光隔离达到最大值的最佳圆柱 - 波导耦合距离。我们的工作有助于理解亚波长运动结构中的非互易性，并可在集成光子电路、拓扑光子学和新型超表面中找到应用。