Half-Integer Topological Charge Polarization of Quasi-Dirac Bound States in the Continuum,Advanced Optical Materials

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Half-Integer Topological Charge Polarization of Quasi-Dirac Bound States in the Continuum
Advanced Optical Materials ( IF 8.0 ) Pub Date : 2023-05-28 , DOI: 10.1002/adom.202300475
Edoardo De Tommasi ₁ , Silvia Romano ₁ , Vito Mocella ₁ , Fabrizio Sgrignuoli ₁ , Vittorino Lanzio ₂ , Stefano Cabrini ₂ , Gianluigi Zito ₁

Affiliation

The non-trivial polarization topology of bound states in the continuum (BICs) provides new strategies in nanophotonics. The polarization topology depends on the geometric parameters and energy-momentum dispersion of the system and can be engineered to add specific functionalities for light molding. Herein, such a possibility is investigated by studying the topology of the polarization states associated with the optical field radiated by BICs when Dirac-cone-degeneracy is lifted. The opening of a pseudogap in the Dirac cone dispersion of square-lattice dielectric photonic crystal slabs is achieved by tuning the slab thickness. First, the emergence of half-integer topological charges without the requirement of BIC annihilation is theoretically shown, which instead occurs when in-plane inversion symmetry is broken. Then, using spin-to-orbital angular momentum conversion, the theory of half-integer topological charges mediated by BICs is demonstrated and experimentally proved. The same device is able to give rise to vortices with different orbital angular momentum depending on the way it is illuminated, thus improving the potential of optical multiplexing. In addition, the additive character of the topology-induced phase-vortex generation is finally demonstrated for both integer and half-integer charges using also vortex states as input beams, which is of relevance for information delivery.

中文翻译：

连续体中准狄拉克束缚态的半整数拓扑电荷极化

连续体束缚态（BIC）的非平凡偏振拓扑提供了纳米光子学的新策略。偏振拓扑取决于系统的几何参数和能量动量色散，并且可以进行设计以添加用于光成型的特定功能。在此，通过研究狄拉克锥简并性解除时与 BIC 辐射的光场相关的偏振态拓扑来研究这种可能性。方晶格介电光子晶体板的狄拉克锥色散中赝能隙的打开是通过调整板厚度来实现的。首先，理论上证明了半整数拓扑荷的出现不需要 BIC 湮灭，而是在面内反演对称性被破坏时出现。然后，利用自旋到轨道角动量转换，证明并实验证明了 BIC 介导的半整数拓扑电荷理论。同一装置能够根据其照射方式产生具有不同轨道角动量的涡旋，从而提高光学复用的潜力。此外，最终还使用涡旋状态作为输入光束，针对整数和半整数电荷证明了拓扑诱导的相位涡旋生成的加性特征，这与信息传递相关。从而提高光复用的潜力。此外，最终还使用涡旋状态作为输入光束，针对整数和半整数电荷证明了拓扑诱导的相位涡旋生成的加性特征，这与信息传递相关。从而提高光复用的潜力。此外，最终还使用涡旋状态作为输入光束，针对整数和半整数电荷证明了拓扑诱导的相位涡旋生成的加性特征，这与信息传递相关。

更新日期：2023-05-28

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