Superior analogs for electromagnetically induced transparency (EIT) and absorption (EIA) in metasurfaces (MSS) are universal, but fewer integrate both effects in one device, let alone contribute to polarization manipulations. Here, note that asymmetrical EITs are rigorously demonstrated under both polarization incidences in dielectric orthogonal dumbbell‐shaped structures, with a maximum group delay of 335 ps. The transverse magnetic (TM) mode excited EIT holds a transparent window at 1.318 THz close to the transverse electric (TE) mode excited that of 1.358 THz, which triggers the linear‐to‐circular polarization conversion at 1.339 THz with an optimized transmittance of 0.67, validated via the axial ratio. Additionally, asymmetrical EIAs are presented with an embedded metal‐phase VO2 plate, holding a common absorption of 0.51 at 1.340 THz, of which the insulating state affects little to the circular‐polarization output. Given the detuning of two frequencies (1.339 and 1.340 THz) can be compensated by the dispersion properties, it can be understood as the original converted circularly polarized propagating light decays with 0.5‐absorption via phase‐tuned VO2, operating as a temperature‐driven switch. The circular‐polarization transmission and absorption are integrated respectively based on EIT and EIA with the different states of VO2, promising broad prospects in multifunctional devices.

In this work, the simultaneous realization of circular-to-linear polarization conversion (PC) and electromagnetically induced transparency (EIT) is theoretically reported in terahertz (THz) range by utilizing a metasurface when left-handed circularly polarized (LCP) waves are incident. The metasurface is composed of two kinds of via-coupled modules (VCMs). Each module can realize the same EIT phenomenon by the destructive interference during the bright and dark modes due to the symmetry-broken rotation operation of the structure instead of the near-field coupling. The VCMs can simultaneously respond to the incident LCP waves and are identically converted into LCP and right-handed circularly polarized (RCP) waves, which own the same amplitudes and phase shifts. Therefore, the LCP and RCP waves can generate a resultant linearly polarized (LP) wave. The EIT transparent windows have emerged in 0.729-1.051 THz during the transmission of the LCP waves and the conversion of LCP to RCP. The values of maximum group delays both are 358 ps. The operating frequency band of the PC is located in 0.65-1.10 THz, and relative bandwidth reaches 51.4%. Optimal relative conversion efficiency reaches 93.2% at 0.921 THz. The EIT behavior has been investigated by the two-oscillator model to further confirm the consistency of the simulation results.

The plasmonic absorbing structure driven by SSPPs has many advantages compared to the planar metamaterial absorber such as achieving customized absorption bandwidth and ultrawideband absorption. [17][18][19][20] Because of the merits of the SSPPs, various configurations based on hole arrays, slits, varactors, or blocks decorated on the metal surface, including the classic waveguide structure, are proposed for different applications. In SSPP modes, the strongly localized oscillation of free electrons can be efficiently trapped at the metalmedium interface. [21][22][23][24] Moreover, it bears mention that promising features of SSPPs in absorption applications have been exploited in several previous research outputs. [13,[25][26][27] For instance, in 2018, Yang et al. developed a non-planar plasmonic structure with a straight wire array as a cover on the absorber to achieve broadband absorption at high frequency and enhance the k-vector matching absorption by dispersion engineering of SSPPs. [28] In 2021, via the dispersion engineering of SSPPs, Zhu et al. designed an active absorptive frequency selective surface supported by a transmission-absorption integrated structure. [25] However, people usually pay attention to transmissionabsorption characteristics of the waveguide structure (WGS) under SSPP modes, and the directionality of EM waves is rarely dug. It can be observed that the overwhelming majority of researches related to metamaterials are confined to the case where EM waves are incident from one side, leaving half of the EM space unexplored. To enhance the capability of EM waves in full space, more original devices should be devised. And it is worth noting that in 2019, directional Janus metasurface (JM) was proposed by Chen et al. to achieve direction control, which increases the degree of freedom of EM waves control. [29] Furthermore, JMs have long been beguiled as a popular concept for breaking out-of-plane and in-plane structural symmetry. [29][30][31][32][33] In another example, Liu et al. raised cascaded chiral metamaterials for different polarization controls in oppositely propagating directions. [33] These works make full use of directional virtues in JM, promoting the flexibility and freedom of EM wave manipulation. On this point, a novel direction-dependent Janus Metasurface (DDJM) with the synergy of SSPP modes is proposed. Different from existing works, inspired by the previous

The polarization of electromagnetic waves is a key feature in the research areas of modern optics and information science. How to efficiently convert the polarization directions of the EM waves remains to be a challenge in electromagnetically induced transparency (EIT). Here, we theoretically propose a double-layer metamaterial with four symmetric H-shaped resonators, which can achieve the EIT phenomenon and transmissive linear polarization conversion (LPC). The EIT effect is acquired depending on the destructive interference between the electric and magnetic resonances. It is demonstrated that electromagnetic coupling is realized by reducing the structural symmetry of the rotated H-shaped resonators. Furthermore, the value of the maximum transmission coefficient reaches up to 0.900 at 14.202 GHz. The values of the transmission dips are 0.094 at 9.913 GHz and 0.176 at 16.101 GHz, respectively. Moreover, a broad transparency window that is higher than 0.8 can be gained spanning from 11.913 GHz to 15.289 GHz, and the relative bandwidth is 24.8%. Meanwhile, the momentous capability of the LPC is also observed. The transmissive cross-polarization conversion is well observed at 9.913 GHz and 16.101 GHz, where the polarization conversion ratios respectively are 90.2% and 91.8%. In the transparent window, a slow-light effect is highlighted. The values of the maximum group delay and group index respectively approach 91 ns and 1925. The FDTD simulation had been employed to further verify the effectiveness of group delay. In particular, the surface current distributions of the H-shaped resonators are employed to explain the mechanisms of the EIT effect and the transmissive LPC. Surpassing the general EIT structures and polarization converters, the proposed metamaterial is synchronously equipped with the EIT behavior and LPC by one same structure, which has numerous potential applications in communication and antenna technologies.

A metasurface (MS) with switching features from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) is theoretically investigated in the terahertz (THz) range by incorporating vanadium dioxide (VO2) when circular polarization‐insensitive circularly polarized waves are incidents, which can also simultaneously realize circular‐to‐linear polarization conversion well. While the VO2 ring is in an insulator state, two new transparent EIT windows both are gained between 0.97 THz and 1.16 THz because of destructive interference between the two metal rings that are seen as bright modes. Once the VO2 ring is tuned to the metallic state, a perfect EIA phenomenon is observed between 0.824 THz and 1.233 THz, achieving the transition from the EIT to EIA behavior well. The received electromagnetic waves are radiated to left‐handed circularly polarized (LCP) or right‐handed circularly polarized (RCP) waves with identical phases and amplitudes through the radiation patches when the LCP or RCP ones are incident. Whereby, a resultant linearly polarized wave is obtained between 0.9 THz and 1.2 THz, and relative bandwidth reaches 29%. The outcomes of maximal group index and group delay both are 1934 and 488 ps at 1.08 THz, and maximal absorption is 90.3% at 1.06 THz.