\begin{document}$2\pi $\end{document} discretely through m unit cells to ensure the complete control of the outgoing waves. The phase gradient provides a new degree of freedom for the manipulation of light propagation, which has allowed a series of ultrathin devices to realize anomalous scattering, the photon spin Hall effect, and many other phenomena.Intuitively, the number of unit cells m in a supercell does not influence the PGM diffraction characteristics, except that a small value of m will lead to a reduced diffraction efficiency. However, some recent studies have shown that the integer m plays a fundamental role in determining the high-order PGM diffractions when the incident angle is beyond the critical angle predicted by the GSL. In particular, for high-order PGM diffractions, m leads to a new set of diffraction equations expressed as                 \begin{document}$ \left\{ {\begin{aligned} &{{k_x} = k_x^t - nG,{\text{ for odd L,}}} \\ &{{k_x} = k_x^r - nG,{\text{ for even L}}{\text{. }}} \end{aligned}} \right. $\end{document}In addition to the phase gradient, the integer number of unit cells m in a supercell is another degree of freedom that can be employed to control the light propagation. By the parity of m, the higher-order outgoing wave can be reversed between the anomalous transmission channel and the anomalous reflection channel.In this work, according to the concept of abrupt phase and the parity-dependent diffraction law in phase gradient metagrating, we theoretically design and study an optical meta-cage. The meta-cage is a periodic structure with one period that contains m different unit cells. Through numerical simulations and rigorous analytical calculations, we find that the ability of meta-cage to trap light is related to the parity of the number of unit cells m in a supercell. Specifically, when the number of unit cells is odd, the point source placed in the meta-cage can perfectly radiate out of the meta-cage without any reflection. On the contrary, when the number of unit cells is even, the point source can hardly radiate out of the meta-cage, and all the energy is localized within the meta-cage. Moreover, such a phenomenon is robust against the disorder. These results can provide new ideas and theoretical guidance for designing new radar radome and photonic isolation devices."> - 必威体育下载

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Citation:

    Gao Yue, Yu Bo-Cheng, Guo Rui, Cao Yan-Yan, Xu Ya-Dong
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    • Abstract views:2796
    • PDF Downloads:63
    • Cited By:0
    Publishing process
    • Received Date:26 August 2022
    • Accepted Date:23 September 2022
    • Available Online:27 October 2022
    • Published Online:20 January 2023

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