Metasurfaces have attracted large interest in recent years due to their relatively simple fabrication, compact design, and ability to control the wavefront of incident light. Ohmic loss attributed to bulk metal metamaterials are not a primary issue, whereby the meta-atom or plasmonic structure is typically only as thin as a fraction of the operation wavelength. Numerous novel applications have been demonstrated by metasurfaces, including an ultrathin metasurface flat lens, and 3D holography.Here, by combining the freedom of both the structural design and the orientation of split ring resonator antennas, we demonstrate Terahertz metasurfaces that are capable of controlling both the phase and amplitude profiles over a very broad bandwidth at~1THz under linearly-polarised incidence. As an example, we show that these phase-amplitude metasurfaces can be engineered to control the diffraction orders arbitrarily.

Metamaterials based on effective media can be used to produce a number of unusual physical properties (for example, negative refraction and invisibility cloaking) because they can be tailored with effective medium parameters that do not occur in nature. Recently, the use of coding metamaterials has been suggested for the control of electromagnetic waves through the design of coding sequences using digital elements ‘0’ and ‘1,' which possess opposite phase responses. Here we propose the concept of an anisotropic coding metamaterial in which the coding behaviors in different directions are dependent on the polarization status of the electromagnetic waves. We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface that functions in the terahertz regime using specially designed coding elements. By encoding the elements with elaborately designed coding sequences (both 1-bit and 2-bit sequences), the x- and y-polarized waves can be anomalously reflected or independently diffused in three dimensions. The simulated far-field scattering patterns and near-field distributions are presented to illustrate the dual-functional performance of the encoded metasurface, and the results are consistent with the measured results. We further demonstrate the ability of the anisotropic coding metasurfaces to generate a beam splitter and realize simultaneous anomalous reflections and polarization conversions, thus providing powerful control of differently polarized electromagnetic waves. The proposed method enables versatile beam behaviors under orthogonal polarizations using a single metasurface and has the potential for use in the development of interesting terahertz devices.

the electromagnetic waves and thus enables versatile functionalities in a planar structure. [15,16] To date, a majority of the studies have been focused on plasmonic metasurfaces involving metallic elements. A prime example is the metasurface composed of spatially varying metallic scatters distributed in one direction. However, plasmonic metasurfaces are difficult to move beyond the limitations of the inherent Ohmic losses and the orthogonal polarization conversion efficiency. [17,18] Efforts have been made to increase the polarization conversion efficiency [10,[19][20][21][22] or to avoid polarization conversion (Huygens surface) by employing multilayer plasmonic metasurfaces, [17,[23][24][25][26][27][28] but these designs introduce other problems. For example, extra loss from dielectric spacers is brought in. Meanwhile, the multilayer design becomes complex and also increases the fabrication challenges.Recently, all-dielectric metasurfaces have drawn enormous attentions. Free from the material loss, all-dielectric metasurfaces have been demonstrated to be able to manipulate lightmatter interactions and manifest exotic photonic behavior with a very high efficiency, far beyond their metallic counterparts. [29] For efficient wavefront engineering, dielectric metasurfaces also play an essential role by utilizing simultaneous excitation of Mie-type electric and magnetic resonances, [30,31] or effective waveguiding effect, [32,33] or the geometric phase concept. [34][35][36] Furthermore, to maximize the usability, controlling the polarization dependence is usually considered in the design. [35][36][37][38][39] However, such studies on dielectric metasurfaces for efficient wavefront engineering thus far, are mainly performed at optical and infrared frequencies. [40] With the rapid development of terahertz technology, the terahertz regime is also in great demand for various highly efficient, flexible, and low-cost functional devices, where the use of the all-dielectric metasurface is a promising solution.In this article, we numerically and experimentally demonstrate polarization-dependent, transmission-type all-silicon dielectric metasurfaces for manipulation of terahertz wavefront. The proposed polarization-dependent metasurface functions as two different devices with respect to the x-and y-polarizations. An efficiency around 60% could be achieved for both the Recently, metasurfaces made up of dielectric structures have drawn enormous attentions in the optical and infrared regimes due to their high efficiency and designing freedom in manipulating light propagation. Such advantages can also be introduced to terahertz frequencies where efficient functional devices are still lacking. Here, polarization-dependent all-silicon terahertz dielectric metasurfaces are proposed and experimentally demonstrated. The metasurfaces are composed of anisotropic rectangular-shaped silicon pillars on silicon substrate. Each metasurface holds dual different functions depending on the incident polarizations. Furthermore, to suppress the r...

Metamaterials offer exciting opportunities that enable precise control of amplitude, polarization and phase of the light beam at a subwavelength scale. A gradient metasurface consists of a class of anisotropic subwavelength metamaterial resonators that offer abrupt amplitude and phase changes, thus enabling new applications in optical device design such as ultrathin flat lenses. We propose a highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime. The proposed structure consists of slotted metallic resonator arrays on two sides of a thin dielectric spacer. By varying the geometrical parameters, the metasurface lens efficiently manipulates the spatial distribution of the terahertz field and focuses the beam to a spot size on the order of a wavelength. The proposed flat metasurface lens design is polarization insensitive and works efficiently even at wide angles of incidence.

Terahertz science and technology promise many cutting-edge applications. Terahertz surface plasmonic waves that propagate at metal-dielectric interfaces deliver a potentially effective way to realize integrated terahertz devices and systems. Previous concerns regarding terahertz surface plasmonic waves have been based on their highly delocalized feature. However, recent advances in plasmonics indicate that the confinement of terahertz surface plasmonic waves, as well as their propagating behaviors, can be engineered by designing the surface environments, shapes, structures, materials, etc., enabling a unique and fascinating regime of plasmonic waves. Together with the essential spectral property of terahertz radiation, as well as the increasingly developed materials, microfabrication, and time-domain spectroscopy technologies, devices and systems based on terahertz surface plasmonic waves may pave the way toward highly integrated platforms for multifunctional operation, implementation, and processing of terahertz waves in both fundamental science and practical applications. We present a review on terahertz surface plasmonic waves on various types of supports in a sequence of properties, excitation and detection, and applications. The current research trend and outlook of possible research directions for terahertz surface plasmonic waves are also outlined.