A general method to realize arbitrary dual-band independent phase control is proposed and demonstrated in this paper. A double-layered C-shape reflective meta-atom is designed to realize independent phase control with high efficiency. As a proof of concept, we propose two functional metasurfaces in the microwave region; the first metasurface performs beam steering in different directions, and the second metasurface generates achromatic beam steering at two distinct frequencies. Both simulation and measurement results agree well with the theoretical pre-setting. The maximum measured efficiency is 88.7% and 92.3% at 6.8 GHz and 8.0 GHz, respectively, for one metasurface, and 91.0% and 89.8% at 6.9 GHz and 8.6 GHz, respectively, for the other.

/pdf/dual-band-independent-phase-control-based-on-high-efficiency-5gd01bcam9.pdf

Dual-band independent phase control based on high efficiency metasurface [Invited]

Tunable metasurfaces are of great potential for the next-generation electromagnetic systems (e.g. beamforming systems due to the capabilities for ultra-fast reconfiguration speed and agile beam programming on the go). The fundamental aspects of tunable metasurfaces laid on their freedom in manipulating the phase and amplitude of the outgoing wavefront. However, the current research heavily focused on the phase manipulation while left the amplitude manipulation capabilities of the metasurfaces barely explored. To unlock the full potential of tunable metasurfaces, in this article, a novel tunable metasurface design with the capability to control both amplitude and phase of transmitted wavefront has been designed, simulated, and characterized experimentally. By incorporating individual phase and amplitude control modules under the guidance of equivalent circuit models, the proposed metasurface achieved the arbitrary phase and amplitude tuning while maintaining reasonably low physical profile. The measurement results of fabricated samples validated the design procedure and fulfilled the flexibility in terms of phase and amplitude tuning, also paved the way towards achieving more powerful dynamic metasurfaces.

/pdf/tunable-metasurface-with-dynamic-amplitude-and-phase-control-17j5784a13.pdf

Tunable Metasurface With Dynamic Amplitude and Phase Control

In order to enhance channel capacity in modern wireless communications, diverse multiplexing techniques, such as polarization, frequency, and spatial multiplexing, are proposed and implemented. Here, a non‐interleaved polarization‐frequency multiplexing metasurface is proposed, which can realize independent controls of orthogonal linearly polarized or circularly polarized waves in two frequency bands to achieve four independent information channels. As a proof of concept, the metasurfaces that can independently realize four different polarized holographic images in two frequency bands are designed, simulated, and measured. The results show that two orthogonally polarized holographic images are achieved in each frequency band, respectively, which can be either linear or circular polarization. Benefitting from the advantages of non‐interleaved design, the proposed metasurfaces can reach not only high information capacity but also high information density by taking full use of the metasurface apertures.

Non‐Interleaved Polarization‐Frequency Multiplexing Metasurface for Multichannel Holography

Simultaneously while independently controlling the phase and amplitude of electromagnetic (EM) waves is pivotal yet challenging for waves manipulation. Metasurface provides a possible approach to the challenge, but most of the reports so far are conducted on linearly polarized EM waves. Herein, a stereo meta‐atom‐enabled gradient metasurface that is capable of fully controlling both amplitude and phase for circularly polarized EM waves is proposed and demonstrated. As a proof‐of‐concept, it is shown that transmission gradient metasurfaces can deflect wave beams by the tailored phase of meta‐atoms and transmission efficiency by the tailored amplitude of meta‐atoms. This study further designs a metasurface to be implemented by stereo meta‐atoms for fan‐shaped beamforming where amplitude and phase gradients are required. The experiments prove that the metasurface realizes a good fan‐shaped beam (azimuthal angle range is −30° to 30°). This study provides an avenue to fully manipulate wave beams by metasurfaces, which may trigger lots of interest in photonic metadevices.

Stereo Meta‐Atom Enabled Phase–Amplitude Gradient Metasurface for Circularly Polarized Waves

A flexible, dual-broadband, and polarization-insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1 bit coding units “0” and “1” are formed by the Pancharatnam–Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this communication can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26–12.87 and 14.84–19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained, while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects. 

Combining Pancharatnam–Berry Phase and Conformal Coding Metasurface for Dual-Band RCS Reduction

Meta-devices have attracted great interest due to the unprecedented capabilities of manipulating wavefronts. Complex-amplitude hologram can provide high-quality images that can be free of ghost images and undesired diffraction orders. However, conventional meta-holograms usually operate at a single band with phase-only modulation. Here, a reflective 2-bit meta-hologram is proposed to operate with independent complex-amplitude modulations at two frequency bands. The high-efficiency meta-atom is composed of a top perforated metallic layer, on which two C-shape split ring resonators (CSRRs) are located in the centers of a circular hole and an annular slot. By tuning the sizes of the two CSRRs, dual-band 2-bit phase modulations can be individually achieved, while the amplitude profile can be continuously tailored at each band by rotating the corresponding CSRR without affecting the phase responses. Based on this emerging meta-atom, a dual-band bifocal metalens is demonstrated numerically and a bispectral meta-hologram is validated both numerically and experimentally at two widely used communication bands. The proposed method features all desirable advantages of the coding metasurfaces with extra degrees of freedom by providing independent frequency control and amplitude modulation, which can provide great opportunities in multifunctional applications with enhanced performance and boosted information capacity.

Frequency-Multiplexed Complex-Amplitude Meta-Devices Based on Bispectral 2-Bit Coding Meta-Atoms

State-to-state photodissociation of CO2(v2 = 0 and 1) at 157 nm via the O(1D) + CO(X1Σ+) channel was studied by using the sliced velocity map imaging technique. Both the O(1D) and CO(X1Σ+) products were detected by (2 + 1) resonance enhanced multiphoton ionization (REMPI). Detection of CO via the B1Σ+ ←← X1Σ+ transition allowed ro-vibrational state-selective detection, and combined with imaging, the fragment energy and angular distributions have been derived. For CO(v = 0 and 1|j) products from the CO2(v2 = 0) molecule, the angular distributions of low-j CO display positive anisotropic parameters (about 0.8); with j increasing, the product anisotropic parameters gradually reduce to zero. While for CO(v = 0 and 1|j) products from the vibrational excited CO2(v2 = 1) molecule, the angular distributions of low-j CO also display positive anisotropic parameters; with j increasing, the product anisotropic parameters first decrease to zero and then become negative (about -0.5). Experimental results show that the observed variation of the product angular distribution with the rotational quantum number of CO is consistent with trends predicted by a classical model for non-axial fragment recoil. The results support advanced theoretical predictions of a predominantly parallel transition to the bent 21A' excited state of CO2, where bending introduces torque during the direct dissociation process.

State-to-state photodissociation dynamics of CO2 at 157 nm.

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Frequency-Multiplexed Complex-Amplitude Meta-Devices Based on Bispectral 2-Bit Coding Meta-Atoms

State-to-state photodissociation dynamics of CO2 at 157 nm.