Nearly Perfect Spin Conversion Based on Topological Singularity in 1D Anisotropic Photonic Crystals.

Although the spin‐controlled vortex generation and photonic spin‐Hall effect of spin‐flipped abnormal mode have been widely studied recently, the traditional method based on the metasurface is difficult to fabricate, and the efficiency of the spin‐flipped abnormal mode is rather low due to process errors and intrinsic material loss. Here, a new method is proposed based on the insights into the topological singularity and special Bragger reflections resonant (BRR) mode of one‐dimensional (1D) finite photonic crystals (PhCs) with anisotropic material to realize nearly perfect (100%) spin‐conversion efficiency. For a finite 1D PhC with cell number N, there are 3N complete spin‐conversion (CSC) and complete spin‐maintained (CSM) channels. Two mechanisms of these CSC and CSM channels are revealed. The working bandwidths and the angular ranges of these CSC and CSM are also studied. Based on these theoretical findings, multi‐angles and multi‐frequencies perfect spin‐conversion (‐maintained) devices can be designed. At last, these theoretical results are confirmed by the numerical experiments based on finite‐difference time‐domain (FDTD) methods. This work paves the way to exploring the topological properties and polarization control of PhCs made of anisotropic dielectrics and provides a prospective method for the design of multi‐channels spin optical devices. [ABSTRACT FROM AUTHOR]