Broadband circular polarization selector and converter based on multilayer metamaterials with stacked split-rings

Metamaterial-based polarization devices are promising in imaging, sensing, and other applications. The balance between multifunction-achieved efficiency and their structural complexity has become an important issue to be discussed. In this paper, we proposed metamaterials with stacked gold split-rings as circular polarization selector and converter for broadband applications that operate in the near-infrared wavelength range. The circular polarization selector consists of six-layer stacked gold split-rings. It can transmit circularly polarized light with the same chirality as the structure and block the orthogonally polarized light. The circular polarization selector works with a bandwidth beyond 700 nm, and its figure of merit is over 11 000. Its operation band can be adjusted by changing the refractive index of the medium, and it has a wide-angle working capability. A circular polarization converter can be obtained by combining two circular polarization selectors with opposite chirality. It works in the range 1460--2100 nm, maintaining the polarization conversion ratio over 0.9 and the ellipticity angle above ${20}^{\ensuremath{\circ}}$. Furthermore, the corresponding physical mechanism was illustrated through the current analysis, and the reliability of the simulated results was verified by the theoretical calculation based on the transfer matrix method. The proposed metamaterial polarization devices can be used in optical communication, biomedicine, and other fields.