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...

Integrating multiple functionalities into a single device is a striking field in metasurfaces. One promising aspect is polarization-dependent meta-devices enabled by simultaneous phase control for orthogonally polarized waves. Among these, Pancharatnam-Berry (PB) metasurfaces have drawn enormous interest owing to their natural and robust phase control ability over different circularly polarized waves. However, the phase responses are locked to be opposite with each other, resulting in interrelated functionalities under the circularly polarized incidence. Here, a generic designing method based on transmission-type dielectric metasurfaces is proposed in the terahertz regime, which breaks this relation by further incorporating dynamic phase with geometric phase, namely, spin-decoupled phase control method. We demonstrate this method by designing and characterizing an efficient multifunctional meta-grating, which splits different circularly polarized waves to asymmetric angles under normal incidences. More importantly, we promote this method by designing several multiplexed meta-gratings for applications of asymmetric polarization generation, which can convert arbitrary linearly polarized wave to two different linearly polarized waves with nearly equal strength and split them to asymmetric angles with a polarization-insensitive efficiency. The designing strategy proposed here shows an impressive robustness and a great flexibility for designing multifunctional metasurface-based devices and opens new avenues toward modulation of polarization states and the application of metasurfaces in beam steering and polarization multiplexing systems.

AbstractCylindrical vector beams (CVBs), being a special kind of beams with spatially variant states of polarizations, are promising in photonics applications, including high-resolution imaging, plasmon excitation, optical trapping, and laser machining. Recently, generating CVBs using metasurfaces has drawn enormous interest owing to their highly designable, multifunctional, and integratable features. However, related studies remain unexplored in the terahertz regime. Here, a generic method for efficiently generating terahertz CVBs carrying orbital angular momentums (OAMs) is proposed and experimentally demonstrated using transmission-type spatial-variant dielectric metasurfaces, which is realized by designing the interference between the two circularly polarized transmission components. This method is based on spin-decoupled phase control allowed by simultaneously manipulating the dynamic phase and geometric phase of each structure, endowing more degree of freedom in designing the vector beams. Two types of metasurfaces which respectively generate polarization-dependent terahertz vector vortex beams (VVBs) and vector Bessel beams (VBBs) are experimentally characterized. The proposed method opens a new window to generate versatile vector beams, providing new capabilities in developing novel, compact, and high-performance devices applicable to broad electromagnetic spectral regimes.

No abstract

Y, et al. (2017) Polarizationindependent all-silicon dielectric metasurfaces in the terahertz regime. Photonics Research 6: 24.