Polarization manipulation associated with electromagnetically induced transparency based on metamaterials

The polarization of electromagnetic waves is a key feature in modern optics and information science research fields. How to effectively control the polarization state of electromagnetic waves in electromagnetically induced transparency (EIT) is still a challenge. Herein, the EIT behavior associated with transmissive linear-to-circular (LTC) polarization conversion is theoretically proposed in the terahertz (THz) regime by employing a metamaterial. Four asymmetric H-shaped resonators are arranged in a cross-shaped arrangement on the metamaterial. It has numerically demonstrated that the electric and magnetic resonances are mutually coupled, leading to the famous EIT phenomenon. Because of the strong dispersion properties and high transmission dominated by the EIT behavior and the anisotropy of metamaterial, the transmissive LTC polarization conversion is conspicuously realized while the x- and y-polarized waves are incidents. Furthermore, two new transparent windows are located in 1.396–1.654 THz and 1.258–1.721THz, which are higher than 0.9 can be gained from 1.409 (1.323) THz to 1.467 (1.594) THz, and the relative bandwidths are 4.0% and 18.6%, respectively. Moreover, the values of the maximum group delay and group index under the x- and y-polarized waves respectively reach 504 ps, 122 ps, and 18861, 4575, displaying a slow-light effect. In addition, the LTC polarization conversion is well obtained at 1.685 THz, where the transmission coefficient highly reaches 0.605. Based on the Stokes parameters, the corresponding ellipticity η, the band of the maximum 3 dB axial ratio, and the polarization azimuth ψ respectively are 0.961, 2.1%, and −42.5°. It is worth noting that not only the thickness of the reported metamaterial is subwavelength, but also the proposed structure with low loss is great transparency for the electromagnetic waves. Surpassing conventional EIT metamaterials and polarization converters, the proposed structure synchronously equipped with those two characteristics has numerous potential applications in the integration to the existing terahertz devices, future polarization controls, and the antenna fields.