Multifunctional All‐Dielectric Metasurfaces for Terahertz Multiplexing

Abstract

Among these multiplexing schemes, Multiple Input Multiple Output (MIMO) spatial multiplexing [8] technology is supposed to be a promising candidate in the terahertz band. The data streams can be transferred in parallel channels simultaneously by antenna array at transmitting and receiving terminals. However, limited by the size and high costs of terahertz antennas, it is still a challenge to realize space multiplexing directly by the antenna array. Instead, high-speed terahertz data transmission could draw lessons from the mode division multiplexing [9] technique, which has been applied in optical communications that uses the orthogonal modes in the fiber as independent channels to transmit data. While for wireless communications, there is not only the fundamental free space mode but also other high order modes, corresponding to the fundamental Gaussian beam and Hermite-Gaussian (HG) beams, respectively, which have been employed in near-field optical imaging, [10] laser communications, [11] and optical communications. [12] The high-order HG modes could be employed as independent channels that resemble the linear polarized modes existing in optical fiber communications, realizing the mode division multiplexing in free-space terahertz communications.However, as the key components in the mode division multiplexing technique, conventional mode conversion and multiplexing devices [13,14] based on natural materials are difficult to simultaneously control the polarization states and the transverse modes. The advance of metasurfaces composed of one or a few layers of artificial resonant meta-atoms provides the solutions to overcome these limitations. Metasurfaces created by periodic lattices of subwavelength meta-atoms can manipulate light with precise control of phase, amplitude, polarization, and momentum. [15][16][17][18][19][20][21] Recently, by giving full play to the modulation freedom of the meta-atoms, it has received more attentions to encode several distinct functionalities in a single metasurface. Until now, these multifunctional metasurfaces have been introduced to realize polarization/wavelengthselective holograms, [22] achromatic devices, [23] vortex beam generators, [24] Huygens surfaces, [25] and frequency mixers. [26] Obviously, multifunctional metasurfaces can replace many common functional devices to simplify the complexity of systems. [27] For example, by integrating an extra meta-axicon or meta-lens phase arrangement into a metasurface design, one Hermite-Gaussian (HG) beams, corresponding to high-order transverse modes, reveal a great potential in the space division multiplexing in optical and wireless communications. Higher data rates are made possible by the introduction of multiplexing, which is critical for next-generation wireless communications working at terahertz frequency. Here, the multifunctional all-dielectric metasurfaces are studied both theoretically and experimentally to implement terahertz mode and polarization division multiplexing. Terahertz incidence with fundamental Gaussian mod...

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