The chiroptical response of the chiral metasurface can be characterized by circular dichroism, which is defined as the absorption difference between left-handed circularly polarized incidence and right-handed circularly incidence. It can be applied in biology, chemistry, optoelectronics, etc. Here, we propose a dynamically tunable chiral metasurface structure, which is composed of two metal split-ring resonators and a graphene layer embedded in dielectric. The structure reflects right-handed circularly polarized waves and absorbs left-handed circularly polarized waves under normal incidence. The overall unit structural parameters of the chiral metasurface were discussed and analyzed, and the circular dichroism was 0.85 at 1.181 THz. Additionally, the digital imaging function can be realized based on the chiral metasurface structure, and the resolution of terahertz digital imaging can be dynamically tuned by changing the Fermi level of graphene. The proposed structure has potential applications in realizing tunable dynamic imaging and other communication fields.

Aiming at the problems that most of the existing electromagnetic metasurfaces have single function and narrow application scope, a highly integrated lightning-type metasurface is proposed in this study. It can realize the functions of circular dichroism (CD), absorption of electromagnetic waves, broadband x-to-y cross polarization conversion (CPC) function, linear-to-circular polarization conversion (LTC-PC) function and asymmetric transmission (AT), and its functions are also analyzed and verified. The designed metasurface consists of the bottom grating structure, the lower SiO2, the middle lightning-type graphene, the upper SiO2, the top graphene and photosensitive silicon. Through numerical calculations, the CD of design can reach more than 85% at 4.22 THz. The function of bimodal absorption is achieved at 4.09 and 8.69 THz. At 7.41∼8.21 THz, the polarization conversion ratio (PCR) of the metasurface reaches more than 99%. Simultaneously, the function of LTC-PC can be formed when PCR is 50%. Finally, when the designed metasurface is in the transmissive state, the AT of design is close to 60% at 7.84 THz. This design provides a new design idea and method for biomedical detection, image processing, modulators, smart switches, optical diodes and other fields.

Tunable multi-function metasurfaces have become the latest research frontiers in planar optics. In this study, a dynamically tunable plasmon-induced transparency (PIT) structure based on a graphene split-ring resonator and graphene ribbon is proposed. The influences of the structural parameters and graphene Fermi energy on the PIT response were investigated both analytically and numerically simulations. The inclusion of an additional vanadium dioxide (VO2) substrate layer enables the metasurface to achieve dynamic switching between PIT and perfect absorption using the phase change property of VO2. The new metasurface device exhibits the PIT effect when the VO2 layer is in an insulating state and acts as a perfect absorber when it is in a metallic state. Moreover, the response of the two functions can be easily adjusted dynamically by changing the Fermi energy of graphene. In addition, both functions were highly sensitive to changes in the ambient refractive index. The results of this work have potential applications in slow-light devices, optical switches, modulators, perfect absorbers, highly sensitive sensors, and multifunctional devices.

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