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We propose a tunable meta-surface in the terahertz regime by patterning a graphene sheet in cut-wire array. The enhancement of terahertz absorption of such a graphene meta-surface was studied detailedly via the optimization to the geometry of the structure. Considering the data of graphene in both the experimental and theoretical perspectives, we investigated the performance of the absorbing graphene meta-surface by extracting its effective surface conductivities through a sheet retrieval method. We also specifically considered two sets of well-known experimental graphene data and comparatively studied the properties of graphene meta-surface by changing the graphene parameters inbetween. It shows that there has been significant improvement in preparing high-quality graphene samples, which makes it possible to strengthen optical properties of graphene microstructures, and therefore benefits various practical applications.

Hyperbolic metasurfaces have recently emerged as a new research frontier because of the unprecedented capabilities to manipulate surface plasmon polaritons (SPPs) and many potential applications. However, thus far, the existence of hyperbolic metasurfaces has neither been observed nor predicted at low frequencies because noble metals cannot support SPPs at longer wavelengths. Here, we propose and experimentally demonstrate spoof plasmonic metasurfaces with a hyperbolic dispersion, where the spoof SPPs propagate on complementary H-shaped, perfectly conducting surfaces at low frequencies. Thus, non-divergent diffractions, negative refraction and dispersion-dependent spin-momentum locking are observed as the spoof SPPs travel over the hyperbolic spoof plasmonic metasurfaces (HSPMs). The HSPMs provide fundamental new platforms to explore the propagation and spin of spoof SPPs. They show great capabilities for designing advanced surface wave devices such as spatial multiplexers, focusing and imaging devices, planar hyperlenses, and dispersion-dependent directional couplers, at both microwave and terahertz frequencies.

We propose a design and numerical study of an optically tunable metamaterial based on an electric-fieldcoupled inductor-capacitor resonator variant in the terahertz regime. In contrast to earlier proposed structures, we demonstrate that a blueshift of the resonance frequency under illumination can be accomplished with realistic material parameters and a broadband tuning range on the order of 40% has been demonstrated, which is found to be based on a photoconductivity-induced mode-switching effect. We also present a variant of this structure, which simultaneously possesses two resonance frequencies and can be used as an optically switchable dual-band resonator. Our all-optical modulators and switches may offer a step forward in filling the "THz gap."

2D optics is gradually emerging as a frontier in modern optics. Plasmons in graphene provide a prominent platform for 2D optics in which the light is squeezed into atomic scale. This report highlights some recent progresses in graphene plasmons toward the 2D optics. The launch, observation, and advanced manipulation of propagating graphene plasmons for 2D optical circuits are described. Representative achievements associated with graphene metasurfaces, challenges, recent progresses like photoexcited graphene metasurfaces, and the transformation optics linking 2D to bulk optics with singularity are investigated.Abstract: Two-dimensional (2D) optics is gradually emerging as the frontier in modern optics. Plasmons in graphene provide a prominent platform for two-dimensional optics in which the light is squeezed into an atomic scale. This paper highlights some recent progresses in graphene plasmons towards the 2D optics. The launching, observation, and advanced manipulations of propagating graphene plasmons for 2D optical circuits are described. Representative achievements associated with graphene metasurfaces, challenges, recent progresses like photoexcited graphene metasurfaces and transformation optics linking 2D to bulk optics with singularity are investigated.

Artificially constructed metamaterials or metasurfaces with tailored resonant elements provide a revolutionary platform for controlling light at the subwavelength scale. Switchable or frequency-agile meta-devices are highly desirable in achieving more flexible functionalities and have been explored extensively by incorporating various materials, which respond to external stimuli. Graphene, a two-dimensional material showing extraordinary physical properties, has been found very promising for tunable meta-devices. However, the high intrinsic loss of graphene severely obstructs us from achieving high-quality resonance in various graphene metamaterials and metasurfaces, and the loss compensation can be considered as a straightforward strategy to take further advantages of enhanced light−graphene interactions. Here, we demonstrate that the photoexcited graphene, in which the quasi-Fermi energy of graphene changes corresponding to optical pumping, can boost the originally extremely weak magnetic resonance in a graphene split-ring metasurface, showing remarkable modulations in the transmission. Our work pioneers the possibilities of optically pumped graphene metasurfaces for significant enhancement of resonances and feasible modulations.

Terahertz time-domain spectroscopy is used to probe the electromagnetic properties of metamaterials, which are dynamically photoexcited, using synchronized femtosecond near-infrared laser pulses. Blueshift tunability of the electric dipole metamaterial's resonance, as well as a broadband phase tunability reaching ϳ / 4, are demonstrated. Numerical simulations show the observations are due to changes in the complex index of the photoexcited semiconductor substrate.

Goos–Hänchen (G–H) effect is of great interest in the manipulation of optical beams. However, it is still fairly challenging to attain efficient controls of the G–H shift for diverse applications. Here, a mechanism to realize tunable G–H shift in the terahertz regime with electrically controllable graphene is proposed. Taking monolayer graphene covered epsilon‐near‐zero metamaterial as a planar model system, it is found that the G–H shifts for the orthogonal s‐polarized and p‐polarized terahertz beams at oblique incidence are positive and negative, respectively. The G–H shift can be modified substantially by electrically controlling the Fermi energy of the monolayer graphene. Reversely, the Fermi energy dependent G–H effect can also be used as a strategy for measuring the doping level of graphene. In addition, the G–H shifts of the system are of strong frequency‐dependence at oblique angles of incidence, therefore the proposed graphene hybrid system can potentially be used for the generation of terahertz “rainbow,” a flat analog of the dispersive prism in optics. The proposed scheme of hybrid system involving graphene for dynamic control of G–H shift will have potential applications in the manipulation of terahertz waves.