Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction ...of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems.
Abstract
Geometric-phase metasurfaces, recently utilized for controlling wavefronts of circular polarized (CP) electromagnetic waves, are drastically limited to the cross-polarization modality. ...Combining geometric with propagation phase allows to further control the co-polarized output channel, nevertheless addressing only similar functionality on both co-polarized outputs for the two different CP incident beams. Here we introduce the concept of chirality-assisted phase as a degree of freedom, which could decouple the two co-polarized outputs, and thus be an alternative solution for designing arbitrary modulated-phase metasurfaces with distinct wavefront manipulation in all four CP output channels. Two metasurfaces are demonstrated with four arbitrary refraction wavefronts, and orbital angular momentum modes with four independent topological charge, showcasing complete and independent manipulation of all possible CP channels in transmission. This additional phase addressing mechanism will lead to new components, ranging from broadband achromatic devices to the multiplexing of wavefronts for application in reconfigurable-beam antenna and wireless communication systems.
Dispersion is one of the key performances of optical systems. As a man‐made device, metasurface is a notable alternative for dispersion manipulation and has been developed vigorously in recent years. ...However, the currently reported dispersion manipulation principle of meta‐atoms only relies on controlling the propagation phase in the operation frequency band or several working wavelengths. In this paper, the chirality‐assisted phase is introduced as an additional degree of freedom to engineer the dispersion characteristics of the meta‐atom, and the strategy is theoretically demonstrated. The dispersion characteristic of the chiral meta‐atom working in a reflective manner is discussed in detail within the working bandwidth. Then, two hybrid dispersion‐engineered metamirrors (HDEMs) are proposed and constructed to demonstrate versatile dispersion manipulation in the working frequency band, including achromatic focusing for the lower half band and hyper dispersive focusing for the upper half band, and hyper dispersive focusing and abnormal dispersive focusing in the lower and upper half band, respectively. Both full‐wave simulation and measured performances verify the validity and flexibility of the proposed strategy. This work exploits a new degree of freedom for dispersion manipulation, providing a new approach for dispersion‐engineered metasurfaces design.
Chirality‐assisted phase is introduced as a new degree of freedom to assist dispersion manipulation more flexibly. As a proof of concept, based on the proposed reflective chiral meta‐atom, two hybrid dispersion‐engineered metamirrors (HDEMs) performing different dispersive focusing within the 8 GHz ‐ 10 GHz and 10 GHz ‐ 12 GHz are proposed and constructed.
An ultrathin flat metalens that experimentally realizes three-dimensional microwave manipulation has been demonstrated as able to approach the theoretical limit of cross-polarization (cross-pol) ...conversion efficiency of the transmission, as predicted by Monticone et al (2013 Phys. Rev. Lett. 110 203903). The helicity-dependent phase change is introduced to the transmission and can be engineered by assembling the spatial orientation of each Pancharatnam-Berry phase element. By realizing the constant phase gradients in orthogonal directions, an anomalous non-coplanar refraction is unanimously demonstrated in the three-dimensional space under the circular-polarized incidence, and the refraction angle is well predicted with the generalized Snell's law, derived with phase gradients in orthogonal directions. More importantly, the maximum conversion efficiency of the cross-pol transmission is as high as 24%, which approaches the upper-bound of the theoretical limit. The proposed metalens has only a single layer as thin as 0.001 , which massively reduces the thickness of the microwave lens along the wave propagation direction. With the great improvements in efficiency and the thickness reduction, as well as the excellent non-coplanar refraction, our design provides a promising approach to miniaturize, planarize and integrate multiple microwave components.
Computational meta-optics brings a twist on the accelerating hardware with the benefits of ultrafast speed, ultra-low power consumption, and parallel information processing in versatile applications. ...Recent advent of metasurfaces have enabled the full manipulation of electromagnetic waves within subwavelength scales, promising the multifunctional, high-throughput, compact and flat optical processors. In this trend, metasurfaces with nonlocality or multi-layer structures are proposed to perform analog optical computations based on Green's function or Fourier transform, intrinsically constrained by limited operations or large footprints/volume. Here, we showcase a Fourier-based metaprocessor to impart customized highly flexible transfer functions for analog computing upon our single-layer Huygens' metasurface. Basic mathematical operations, including differentiation and cross-correlation, are performed by directly modulating complex wavefronts in spatial Fourier domain, facilitating edge detection and pattern recognition of various image processing. Our work substantiates an ultracompact and powerful kernel processor, which could find important applications for optical analog computing and image processing.
Geometric metasurfaces primarily follow the physical mechanism of Pancharatnam–Berry (PB) phases, empowering wavefront control of cross‐polarized reflective/transmissive light components. However, ...inherently accompanying the cross‐polarized components, the copolarized output components have not been attempted in parallel in existing works. Here, a general method is proposed to construct phase‐modulated metasurfaces for implementing functionalities separately in co‐ and cross‐polarized output fields under circularly polarized (CP) incidence, which is impossible to achieve with solely a geometric phase. By introducing a propagation phase as an additional degree of freedom, the electromagnetic (EM) energy carried by co‐ and cross‐polarized transmitted fields can be fully phase‐modulated with independent wavefronts. Under one CP incidence, a metasurface for separate functionalities with controllable energy repartition is verified by simulations and proof‐of‐principle microwave experiments. A variety of applications can be readily expected in spin‐selective optics, spin‐Hall metasurfaces, and multitasked metasurfaces operating in both reflective and transmissive modes.
A general scheme based on a phase‐modulated metasurface for simultaneous and independent manipulation of co‐ and cross‐polarized wavefronts is proposed, which breaks through the inherent limitation of the geometric phase principle and achieves full energy modulation in output fields. The energy proportion between two orthogonal CP output functionalities can also be artificially manipulated as an extra freedom of degree for light manipulation.
Chitin is the second most abundant biopolymer in nature and has tremendous potential in renewable materials for packaging, energy storage, reinforced composites, and biomedical engineering. Despite ...attractive properties, including biodegradability, antibacterial activity, and high strength, chitin is not utilized widely due to strong molecular interactions, which make solubilization and processing difficult. We report a high pressure homogenization route to produce pure chitin nanofibers (ChNFs) starting with a mildly acidic aqueous dispersion of purified crab α-chitin. The well-dispersed ChNFs with diameter ∼20 nm do not form strong network structures under conditions explored herein and can be directly processed into useful materials, bypassing the need to dissolve the chitin. Dried ChNFs form pure self-standing chitin films with the lowest to-date reported O2 and CO2 permeabilities of 0.006 and 0.018 barrer, respectively. Combined with high flexibility and optical transparency, these materials are ideal candidates for sustainable barrier packaging.
In this paper, a holographic metasurface possessing beam scanning capability at fixed frequency is presented. The desired radiation beam is obtained by using a reference wave to excite a ...sinusoidally-modulated impedance surface, which is equivalent to the interference pattern between the radiation wave and reference wave. By changing the bias voltage of varactor diodes loaded on the sub-wavelength unit cells, the variation range of the modulated impedance can be tuned, resulting in the change of radiation angle. Both the simulation and experimental results demonstrate that the direction of the radiation beam can be tuned in the range from 23° to 50° at 5.5 GHz. The proposed holographic metasurface shows great potential applications in constructing planar beam scanning antenna for integrated microwave system.
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