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Signal conversion plays an important role in many applications such as communication, sensing, and imaging. Realizing signal conversion between optical and microwave frequencies is a crucial step to construct hybrid communication systems that combine both optical and microwave wireless technologies to achieve better features, which are highly desirable in the future wireless communications. However, such a signal conversion process typically requires a complicated relay to perform multiple operations, which will consume additional hardware/time/energy resources. Here, we report a light-to-microwave transmitter based on the time-varying and programmable metasurface integrated with a high-speed photoelectric detection circuit into a hybrid. Such a transmitter can convert a light intensity signal to two microwave binary frequency shift keying signals by using the dispersion characteristics of the metasurface to implement the frequency division multiplexing. To illustrate the metasurface-based transmitter, a hybrid wireless communication system that allows dual-channel data transmissions in a light-to-microwave link is demonstrated, and the experimental results show that two different videos can be transmitted and received simultaneously and independently. Our metasurface-enabled signal conversion solution may enrich the functionalities of metasurfaces, and could also stimulate new information-oriented applications.

Metasurfaces, composed of prearranged artificial unit cells possessing different electromagnetic (EM) responses, provide unprecedented abilities to realize versatile wave manipulations. Especially in the terahertz spectrum, metasurfaces attract broad attention by opening up further possibilities for wave regulating. Terahertz applications in various fields, for instance, spatial light modulation (SLM), radar, imaging, time-domain spectroscopy (TDS), and high-speed communication, have been facilitated and improved. In this article, we first give a simple review on recent advances on terahertz metasurfaces, including discussion of passive metasurfaces with fixed structures and active metasurfaces integrated with tunable components. Then, we briefly review the development of coding metasurfaces and programmable metasurfaces represented by digitized bits. We mainly focus on some powerful functions, functional multiplexing, and real-time controlled applications in terahertz frequencies. Finally, we give an abbreviated overview of developing terahertz multifunctional metasurfaces and programmable metasurfaces.

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Metasurfaces provide an unprecedented capability in manipulating electromagnetic waves. In this work, a millimeter-wave (mmW) digital coding metasurface based on nematic liquid crystals (NLCs) is proposed and realized. By tuning the bias voltage loaded on the NLCs, the effective permittivity of the NLCs substrate is changed, thus providing different reflection phases. As a proof of concept, mmW beam splitting and mmW beam steering at mmW frequencies are demonstrated using a single metasurface platform. The experimental results are in good agreement with numerical simulations. The proposed digital coding metasurfaces have promising applications on planar mmW devices, such as multi-beam antennas, beam-scanning antennas, and wave controllers. Design and SimulationLiquid crystals (LCs), in real applications, are commonly used as display material, that is, liquid crystal displays (LCDs). Actually,

Manipulating the phase, polarization, and energy distribution of electromagnetic (EM) waves has facilitated numerous applications. Nowadays, metasurface provides an innovational scenario to carry out more promising and advanced control of EM waves. However, it is a great challenge to manipulate polarization, phase, and energy distribution simultaneously with a low profile. Herein, a class of single-layer radiationtype metasurfaces to achieve advanced EM manipulation is proposed. Desired EM functions can be achieved based on the geometric phase and resonant phase. Such metasurfaces enable the capability to manipulate arbitrary phases and linear polarization states simultaneously. Moreover, arbitrary energy distributions can be controlled. As examples of potential applications, three advanced EM functional devices are presented: a novel multiple-input multiple-output antenna with efficient crosstalk suppression and information encryption, an energy-controllable router, and a metasurface holographic imaging based on power transmission algorithm, respectively. The proposed strategy may open up an alternative way of controlling EM waves with advanced performance and minimalist complexity. Moreover, it may lead to advances in information encoding and cryptography.

Metasurfaces exhibit promising capacities in the manipulation of electromagnetic (EM) waves, as to diverse dimensions like amplitude, phase, and polarization; even multiple dimensions can be synchronously modulated. Despite the rapid progress in enriching regulatory capabilities of EM waves, primary feeds are integral items however bringing profile elevation, energy obstruction, and leakage, both for reflection‐type and transmission‐type metasurfaces. Aiming at maintaining high operating efficiency and in meantime implementing multiple dimensional manipulations of EM waves, the authors present a concise design of radiation‐type metasurfaces, whose distinctive feature stands that each meta‐atom serves not only as geometry phase provider, but as radiator itself so as to spare primary feeds. To further achieve full phase modulation for arbitrary linear polarized radiations and abate innate conjugacy to orthogonal circular polarized radiations, the propagation phase is introduced irrelevant to geometry ones. Based on the radiation‐type metasurface with 0.07‐wavelength low profile, the authors verify experimentally advanced radiation functions for different polarizations like orbital angular momentum beams, asymmetric beams, and time‐reversed focusing. Compared with traditional planar arrays that rely on feeding networks to realize phase modulation, this design provides the possibility to achieve direct phase and polarization modulation at the element level, thus is with less complexity.