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Holography has attracted considerable interest because of its excellent capacity of recording and perfectly reconstructing the target information. The emergence of metasurfaces provides a new medium to code holograms in the subwavelength scale. Phase‐based holograms reported so far intrinsically decrease the image fidelity, because the amplitude information is ignored, especially for circularly polarized (CP) holograms. Herein, a novel strategy is proposed to achieve complex‐amplitude (CA) meta‐holography for CP transmissive waves with high fidelity and high polarization purity. Two cascaded patches are used to realize an amplitude modulation of 0–0.97 and a 2π phase shift in the microwave region. To verify and prove the concept, two CA meta‐holograms are designed, fabricated, and measured. The theoretical structural similarity index is 0.94 for the meta‐hologram reconstructing the letter “L” and 0.89 for the meta‐hologram reconstructing the Chinese character “”. It is experimentally demonstrated that the proposed CA method performs better, yielding higher‐accuracy reconstructed images than the phase‐only method. The polarization purity in the reconstructed images can be higher than 20 dB. The finding paves the way for synthesizing arbitrary wave‐front shapes and can find several applications in communication systems, imaging construction, and information processing.

Metasurface-based vortex beam generators are very promising and applicable to enhance transmission data capacity in wireless communication system. However, most designs to date are ceased to predict their far-field characteristic, which is actually in demand when applied to wireless communication. Here, we find for the first time a deterministic and robust strategy to fastly estimate the exact far-field patterns and gain limit of a vortex beam based on the theoretical analysis of aperture field with spiral phase profile. For verification, a broadband metasurface-based vortex-beam generator based on geometric phase is designed, numerically calculated and experimentally measured at microwave regime. Excellent agreements are observed among far-field results obtained based on the proposed method, numerical simulations and experimental measurements, firmly demonstrating the validity and correctness of the proposed strategy. Such a deterministic and robust strategy of predicting far-field characteristics of a vortex beam may pave the way for its applications in many engineering scenarios, such as conical beam design, wireless communication, et al.

Polarization, amplitude and phase are three critical characteristics of electromagnetic waves as known. In this article, a general method with high efficiency and low complexity is proposed to realize simultaneously independent control of polarization, amplitude and phase of electromagnetic waves by receiver-transmitter integrated meta-atoms in transmissive geometry. The amplitude modulation is controlled by the rotation angle of top receiver patch, while the phase delay is determined by the rotation angle of bottom transmitter patch without affecting the amplitude. In addition, the polarization is controlled by the polarization of both receiver and transmitter. As a proof of concept, a metasurface with multiple diffraction orders is designed, fabricated and measured in microwave reigonnnogier. The measured results are in excellent agreement with the simulated ones. Our finding offers an alternative way to synthesize arbitrary wavefront shapes of EM waves, and we are looking forward to more highperformance photonic metadevices by applying this approach.

Metasurfaces enable a new route to control electromagnetic waves by manipulating artificial structures with subwavelength. Despite the rapid growth, the meatasurfaces realized so far largely reply on passive resonant meta-atom, whose functionality is limited once the metasurfaces are fabricated. Here, based on incorporating active varactor diodes into the meta-tom, tunable reflection phase can be achieved. In this paper, a programmable meta-atom with multiple resonance structure, resulting in tuning full 360° reflective phase, is presented and simulated. The proposed meta-atom integrating three varactor diodes has two resonance poles and one resonance zero in between when illuminated by y-polarized plane wave. Owing to two resonances connected to each other, the reflection phase can cover the whole 360° range without the asymptotic behavior. The presented programmable meta-atom may offer unprecedented potentials for real-time, fast, and sophisticated electromagnetic wave such as dynamic focusing, beam steering, imaging, photonic spin-Hall.

Manipulating orthogonal circularly polarized (CP) waves independently in both reflection and transmission modes in a single metasurface is pivotal. However, independently controlling CP waves with different polarizations is difficult especially for both reflection and transmission modes. Here, we designed a receiver-transmitter metasurface with helicity-dependent reflection and transmission properties. Our design breaks the fixed phases of the geometry metasurface-carrying Pancharatnam-Berry operators by combining the receive and transmit antennas. To verify the effectiveness of the modulation, we designed three linear deflectors with: (a) reflection phase gradient, (b) transmission phase gradient, and (c) both of gradients to achieve anomalous reflection, anomalous refraction, and simultaneous anomalous reflection and refraction, respectively. As proof of the concept, a bifunctional meta-device with functions of anomalous reflection and focusing transmission for different incident CP waves was simulated and measured. Our findings offer an easy strategy for achieving arbitrary bifunctional CP devices.

Supplemental Documen

A dual-mode and dual-band flat high-gain antenna based on anisotropic focusing metasurface (MS) is proposed in this communication. The elements of the MS can steer the reflected phases of ${y}$ -polarized waves around 10 GHz and the transmitted phases of ${x}$ -polarized waves around 14 GHz independently. The function of the anisotropic MS is to focus the incident plane waves around 10 and 14 GHz on spots with different focal lengths and spaces. To reduce the block effect of the reflection mode, an extra phase gradient is introduced to the initial phase distribution of the ${y}$ -polarization to deflect the reflection mode main-beam to an angle of 30°. Finally, the new high-gain antenna obtains a deflecting reflection beam with peak gain of 17.2 dB and a normal transmission beam with peak gain of 19.5 dB. Besides single-band working, the antenna can also operate at 10 and 14 GHz simultaneously with gains of 14.7 and 16.7 dB, respectively. Measured results make a good agreement with the simulated results.

A single-layer focusing gradient metasurface (MS) built by one element-group is proposed. The element-group is designed by well connecting the phase shift range of two similar single-layer elements under the condition of transmitting efficiencies over 0.7. The proposed MS can focus the propagating plane wave on a point and a patch antenna is placed at its focus to build a high-gain planar lens antenna. This lens antenna achieves pencil-shaped far-field radiation pattern with a simulation peak gain of 16.7 dB at 10 GHz. The single-layer structure makes it easy to fabricate the MS with low profile and satisfying performances. Finally, the MS and the patch antenna are fabricated, assembled, and measured. The measured results are in good agreement with the simulations.

Recently, metasurfaces (MSs) have received tremendous attention because their electromagnetic properties can be controlled at will. Generally, metasurface with hyperbolic phase distributions, namely, focusing metasurface, can be used to design high-gain antennas. Besides, metasurface has the ability of controlling the polarization state of electromagnetic wave. In this chapter, we first propose a new ultrathin broadband reflected MS and take it into application for high-gain planar antenna. Then, we propose multilayer multifunctional transmitted MSs to simultaneously enhance the gain and transform the linear polarization to circular polarization of the patch antenna. This kind of high-gain antenna eliminates the feed-block effect of the reflected ones.

A perfect absorber is highly desired in many engineering applications, including cloaking devices and sensor detectors, but most types of absorbers with chirality-dependence have limited bandwidth. In this paper, we propose a novel broadband and chirality-dependent metasurface absorber that consists of an array of planar spiral elements. The spiral orientation can determine the absorption polarization, such as counterclockwise for right circular polarization (RCP) absorption and clockwise for left circular polarization (LCP) absorption. Three steps are adopted to enhance the absorption bandwidth: carefully optimizing the spiral turns, impedance of load resistor, and introducing a matching layer. To demonstrate our concept, we have designed and fabricated a realistic metasurface absorber. The numerical simulations are in good agreement with the experimental results. The simulation and measurement results demonstrate that this device can achieve a broadband (8.3-18 GHz) absorption for RCP incidence, while reflecting the LCP incident waves between 9 GHz to 17.8 GHz without changing its chirality. Our findings explore a novel way to realize broadband absorption and simultaneously provide a new strategy to design chirality-dependent multi-functional meta-devices.

Metasurfaces continue to drawn significant attention for manipulating light waves, but most to date have controlled either the phase profile or the amplitude profile of the output light---not both. This study proposes a strategy to control the transmitted phase and amplitude, over a wide band. A compound meta-atom can control the transmitted phase by modulating the gap size of a modified I-shaped structure, and can set the transmitted amplitude by rotating the structure between outer gratings. A proof-of-concept experiment points to the possibility of realizing arbitrary beam shapes.

Achieving simultaneous controls of the amplitude and phase for electromagnetic waves is essential when shaping a complete wave-front aimed at forming an arbitrary beam. Here a strategy of manipulating the reflected amplitude and phase is proposed using a bi-layered metasurface element. The metasurface unit cell, consisting of a modified I-shape particle and one all-metal ground, achieves broadband phase- and amplitude control by tuning the gap size and rotating the modified I-shape particle, respectively. As a proof of concept, we design a fan-shaped beam metasurface antenna using the genetic algorithm to obtain the optimal phase and amplitude distributions. A Vivaldi antenna with less blockage effect is chosen to illuminate the metasurface, and then the amplitude and phase are compensated by the elements to achieve the optimized distributions. Finally, the beam-forming metasurface antenna is simulated, fabricated, and measured. The results show that the metasurface can generate a flat top beam under rectangular coordinate within the frequency range of 9–12 GHz. Our findings not only provide a universal way for generating beams with arbitrary shapes using metasurfaces but also offer an economical and simple alternative for a beam-forming array antenna.

Metasurfaces (MSs) attract significant attention and are widely applied in modern communication systems due to their powerful capabilities to control the polarization, amplitude, and phase of electromagnetic (EM) waves. However, it is considerably challenging to control polarization and amplitude of incident waves for a passive metasurface. Specifically, we integrate the transmission and reflection functions by loading a middle layer with PIN diodes while the upper and lower structures are used to manipulate the polarizations of incident waves. As a proof of concept, we fabricate a sample having 18 × 18 meta-atoms. Beam deflectors for the circularly polarized waves dependent on Helicity are realized when the PIN diodes are turned off. A transmissive polarization converter for x-polarization and a reflective polarization keeper for y-polarization are achieved as the PIN diodes are turned on. More importantly, the functionalities exhibit extremely high efficiencies in the range 86.4–90.3% for reflective functionalities and 75.4% for transmissive functionalities. Our findings provide a new method to design multifunctionalities metasurface via tunable devices and yield many applications in multifunctional systems.

In this paper, an ultra-thin single-layered transparent metasurface (MS) is proposed to focus circularly polarized (CP) waves in transparent geometry with high efficiency. A single-layered phasing element is firstly optimized to meet the demands of Pancharatnam-Berry (PB) phase theory. Firstly, a one dimensional phase gradient MS is devised with phase difference of 60°between adjacent cells, in order to validate the surface capability of manipulating transmitted waves. Secondly, a novel planar focusing metasurface (PFM) is designed with focal length of 40mm and size of 102×102mm2 as well as cells of 15×15. The pretty good focusing effect of the CP metasurface lens contributes to its application for high gain lens antenna. Finally, by placing a CP patch antenna at the focal spot of the PFM as the feed source, the excellent performances of the MS lens antenna are obtained in terms of realized gain of 20.7 dB, aperture efficiency of 41.3%, half power beam width (HPBW) of 14° near 14GHz.

In this paper, a novel multifunctional metasurface combining linear-to-circular polarization conversion and electromagnetic waves focusing has been proposed and applied to design a high-gain lens antenna working at Ku band. The multifunctional metasurface consists of 15 × 15 unit cells. Each unit cell is composed of four identical metallic layers and three intermediate dielectric layers. Due to well optimization, the multifunctional metasurface can convert the linearly polarized waves generated by the source to circularly polarized waves and focus the waves. By placing a patch antenna operating at 15 GHz at the focal point of the metasurface and setting the focal distance to diameter ratio (F/D) to 0.34, we obtain a multifunctional lens antenna. Simulated and measured results coincide well, indicating that the metasurface can convert linearly polarized waves to right-handed circularly polarized waves at 15 GHz with excellent performances in terms of the 3 dB axial ratio bandwidth of 5.3%, realized gain of 16.9 dB and aperture efficiency of 41.2%. Because of the advantages of high gain, competitive efficiency and easy fabrication, the proposed lens antenna has a great potential application in wireless and satellite communication.

Multi-functional metasurfaces have exhibited powerful abilities of manipulating electromagnetic (EM) wave in predetermined manners, largely improving their information capacities. However, most works are implemented with EM functions controlled by one of the intrinsic properties of EM wave, such as polarization, frequency, etc. Herein, we propose a coding scheme to design a broadband and high-efficient multi-functional metasurface independently controlled by both frequency and polarization. To achieve this goal, we design anisotropic coding particles to realize independent phase functions and polarization-selectivity in the microwave region. Meta-atoms are finally optimized to exhibit 2-bit phase responses insensitive to incident polarization in the X-band while showing a 1-bit phase shift sensitive to incident polarization in the Ku-band. As a proof of concept, a metasurface is configured as an isotropic lens in the X-band, whereas the metasurface is designed as an anisotropic beam deflector in the Ku-band with or without polarization-conversion functionality dependent on the input polarization. The measured results, which agree well with the simulated ones, show excellent performances in the designed dual bands. Such a multi-functional coding metasurface may provide a flexible and robust approach to manipulate EM wave of multiple frequencies, as well as to integrate diverse functionalities into a single flat device.

Achieving asymmetric transmission effects, especially in an ultra-broadband frequency region, is of particular importance in communication systems. Currently available asymmetric transmission metasurfaces are limited to narrow bands and low efficiencies because of the inherently dispersion effects and large transmission fluctuations. In this paper, we propose a new strategy to realize high efficiency and ultra-broadband asymmetric transmission in an ultra-thin profile by using the topologically coding optimization method. The meta-atom consists of two outer orthogonal gratings and a central lattice particle optimized by genetic algorithm. The optimized central lattice suppresses the transmission fluctuations by tuning the coupling among different metallic layers, resulting in very broad band and high transmissions. Experimental results show that our metasurface achieved perfect reflection over 95% and high cross-polarization transmission over 80% for y- and x-polarized incidence from 5.3 GHz to 16.7 GHz, respectively. Our findings pave a way to high-performance and broadband polarization transformers and polarization-controlled devices working in different frequency domains.

In this letter, an ultra-thin anisotropic metasurface cell with independent control of different polarized waves is introduced firstly. Then different sizes of cells are taken to constituted an anisotropic planar focusing metasurface(PFM) lens with size of 102 × 102mm2. Experimental results are in excellent agreement with the simulated ones, indicating perfectly focusing effect of the PFM lens. Moreover, different focal lengths of 50 mm and 30 mm are demonstrated for x/y-polarized incident waves.

As an ultra-thin developed form of meta-materials, metasurface does attract tremendous attention due to its flexibility in controlling wave front in different spectrums. In this paper, we propose a microwave metasurface with function of transforming spherical waves into plane waves and splitting waves according to polarized status of incident waves. By using a compact ultra-thin anisotropic element, we design a polarization beam splitter under spherical wave's illumination. With different phase gradients for x/y-polarized waves, the anisotropic metasurface has function of gain enhancement of 12.4 dB on average and reflecting x/y- polarized waves in -x/+y direction with the same reflected angel of 33° at the operating frequency of 15GHz. For verification of simulation results, the metasurface sample with size of 102×102mm2 and cells of 17×17 is fabricated and measured. Experimental results are in excellent agreement with the simulated ones, in which the high isolation of 30dB at 15GHz between x- and y-polarized waves is obtained. Due to the great performance in beam steering and thickness reduction, our design provides a promising approach of beam splitting, steering and gain enhancement in microwave region.

In this paper, we propose a polarization beam splitter utilizing an ultra-thin anisotropic metasurface. The proposed anisotropic element is composed of triple-layered rectangular patches spaced with double-layered dielectric isolators. By tailoring the metallic patches, the cell is capable of transmitting x-polarized waves efficiently and reflecting y-polarized beams with almost 100% efficiency at 15 GHz. In addition to this, the reflected phases can be modulated by adjusting the size of the element, which contributes to beam steering in reflection mode. By assigning gradient phases on the metasurface, the constructed sample has the ability to refract x-polarized waves normally and reflect y-polarized beams anomalously. For verification, a sample with a size of 240 240 mm2 is fabricated and measured. Consistent numerical and experimental results have both validated the efficiently anomalous reflection for y-polarized waves and normal refraction for x-polarized beams operating from 14.6–15.4 GHz. Furthermore, the proposed sample has a thickness of 0.1λ at 15 GHz, which provides a promising approach for steering and splitting beams in a compact size.