Dynamic inversion of planar-chiral response of terahertz metasurface based on critical transition of checkerboard structures

Dynamic inversion of the planar-chiral responses of a metasurface is experimentally demonstrated in the terahertz regime. To realize this inversion, the critical transition of the checkerboard-like metallic structures is used. Resonant structures with planar chirality and their complementary enantiomeric patterns are embedded in the checkerboard. Using vanadium dioxide as a variable resistance, the metasurface is implemented in the terahertz regime. The responses of the metasurface to circularly polarized waves are then characterized by terahertz time-domain spectroscopy. Further, the sign of the circular conversion dichroism, which is closely related to the handedness of the planar chirality of the metasurface, is observed to be inverted at 0.64 THz by varying the temperature. Such invertible planar-chiral responses can be applied practically to the handedness-invertible chiral mirrors.

Ultrathin Spin-Decoupled Meta-Devices for Independent Control of Electromagnetic Waves With Dual-Orthogonal Circular Polarization

Inspired by the concept of miniaturized and integrated systems, an ultrathin and multifunctional metasurface device is highly desirable in microwave fields. It is an inherent characteristic that the two spin phase states of electromagnetic waves imparted by the geometric phase are always conjugate symmetric, i.e., the geometric phase produces anti-symmetrical phase responses between dual-orthogonal circular polarization states. So it is extremely crucial to break the conjugate constraints and realize the completely independent control of electromagnetic waves with dual-orthogonal circular polarization. Based on this perspective, ultrathin and bifunctional meta-devices operating in reflection mode are proposed to independently manipulate the left-handed and right-handed circularly polarized waves, which are constructed by anisotropic meta-atoms with synthetical geometric and propagation phases. It is worth noting that the component elements only need a single-layer structure with the thickness of 0.07λ0. Several design samples are presented to achieve functionalities of beam focusing, vortex wave generation, and beam deflection, respectively. Experiments are performed and show good consistence with the simulation results, successfully verifying the performance of the designed metasurfaces. The research results in this paper pave the way to design low-profile and bifunctional devices with independent controls of circularly polarized waves, which is expected to expand the working capacity of metasurfaces to realize complex electromagnetic wave manipulation with a new degree of freedom.

Evolution equation for interaction of opposite directed waves with arbitrary polarization in 1D-metamaterial

In this paper, a theoretical study of wave propagation in 1D metamaterial is presented. A system of evolution equations for electromagnetic waves with both polarizations account is derived by means of projection operators method for general nonlinearity and dispersion. It describes interaction of opposite directed waves with a given polarization. The particular case of Kerr nonlinearity and Drude dispersion is considered. In such approximation, it results in the corresponding system of nonlinear equations that generalizes the Schäfer–Wayne one. Traveling wave solution for the system of equation of interaction of orthogonal-polarized waves is also obtained. Dependence of wavelength on amplitude is written and plotted.

Tunable polarization comb based on the electromagnetically induced transparency with hybrid metal-graphene metamaterial

Noted a linear-to-circular polarization comb based on electromagnetically induced transparency (EIT) with hybrid metal-graphene metamaterial in terahertz (THz) spectroscopy. Due to the near field coupling between the bright mode of metal cut-wire (MCW) and multiple dark modes, the multi-peak EIT effect is exhibited under the x-polarized incidence supported by the three-level theory. With another orthogonal MCW etched on the back of the SiO2, the asymmetry responses in both polarized incidences (x- and y-polarized waves) further triggers the linear-to-circular polarization conversion (LTCPC). The values of four corresponding circular-polarized frequencies combined with transmission coefficients respectively are 0.90 THz with 0.45, 1.02 THz with 0.64, 1.15 THz with 0.60, 1.32 THz with 0.53, confirmed via relevant axial ratios and the electric field distributions. On the other hand, the drastic phase changes in transparent windows raise high group delays, among which the maximum value approaches 325 ps. Additionally, DC-voltage-driven graphene strips are doped at both ends of the back MCW to enhance the reconfigurability, superior tunable transmission behaviors illuminated by y-polarization with obvious changes at 0.90 THz and 1.02 THz can be achieved with the dynamic Fermi level fluctuating between 0.01 eV and 0.8 eV. Such an implementation creates a novel path to polarization modulators, signal transceivers, and information transmission devices.

Bi-functional Metasurface Polarizer for Reflected and Transmitted Waves

Manipulating the polarizations of electromagnetic waves by flexible and diverse means is desirable for a myriad of microwave systems. More recently, metasurfaces offer the promising alternatives to conventional polarization manipulating components because of the flexibility of their geometry could be arbitrarily customized. In this context, a bi-layered metasurface was presented to simultaneously manipulate the polarized states of reflected and transmitted microwaves. No matter whether the incident electromagnetic wave is x-polarized or y-polarized, the reflected and transmitted waves will be converted into orthogonal y- polarized waves at the operating frequency. The designed metasurface has a high polarization conversion rate(PCR) above 90% for both normal and oblique incidence. The experimental results verify the correctness of the simulated results. Finally, axial ratio and surface current distributions were employed to reveal the physics of polarization manipulation. The proposed metasurface will be beneficial to the design of flexible and versatile polarization converters and has great potential for applications in polarization controlled devices and also is believed extendable to higher frequency regimes.