Search

We present a polarization-selective transmission-type 2 bit coding metasurface (MS) to achieve dual-band performance, in which the operating frequency band is adjustable between the lower (Ku-band) and higher (K-band) bands by changing the polarization of the linearly polarized incident wave. Three coding MS devices are designed by using specific coding sequences of the proposed coding meta-atoms. Firstly, two coding MSs are presented for vortex beam generation that carries orbital angular momentum with different topological charges in the two operating bands. Secondly, a coding MS is proposed to anomalously refract the cross-polarized field with different deflection angles in the two frequency bands. Finally, the proposed scheme is extended to design a coding MS that focuses the transmitted fields at two frequencies by changing the polarization of the incident wave. Furthermore, the proposed designs are valid to perform the same functions for waves propagating along both the ‘+z’ and ‘−z’ directions in the same frequency bands but with orthogonal polarizations of incident waves. The sign of the topological charge can be altered by changing the direction of propagation from ‘+z’ to ‘−z’. To demonstrate the easiness of implementations, experiments of the fabricated samples are performed for the vortex beam generation and focusing. We believe that the proposed method may find potential applications in the future optical devices for multi-spectrum and multi-function operations. [ABSTRACT FROM AUTHOR]

Multiple band-rejection filters based on spoof surface plasmon polaritons (SPPs) are designed in dual frequency bands using interactions between spoof SPP waveguide and metamaterial particles. The multi-band rejections are achieved by etching π-type decorations on the spoof SPP waveguide. More importantly, the bandwidths, isolation and shifting of the rejection frequencies of filters can be controlled very efficiently by varying different geometrical parameters of the π-type decorations. Both numerical and experimental results are demonstrated to verify the large flexibility and excellent functionality of the multiple band-rejection filters in both lower and higher frequency bands. We are fully confident that the use of two frequency bands in realizing multiple band-rejections filtering by the proposed spoof SPP waveguide makes it unique in giving a boost to the development of plasmonic integrated circuits and systems. [ABSTRACT FROM AUTHOR]

Metasurfaces provide the freedom to manipulate electromagnetic (EM) waves by controlling the peculiarity of subwavelength artificial structures. Many exciting devices have been developed using metasurfaces that can even perform multiple functionalities. In this paper, we propose to transform linearly polarized EM waves into high-order orbital angular momentum (OAM) beams and specifically reflected split beams for different polarizations based on anisotropic coding metasurfaces. By means of precisely adjusting the geometry of the element structure, the reflection phases of two perpendicular polarizations can be encoded without interference, which is conductive to encode the metasurfaces independently in two different directions. Under this benefit, two kinds of 2-bit phase-coded metasurfaces are constructed and verified by experiments to demonstrate their versatility of generating effective high-order OAM beams and specified reflected split beams, respectively. Beyond that, by adjusting the coding scheme, more features can be implemented under this merit. [ABSTRACT FROM AUTHOR]

An illusion device based on a shifting-distance concept has been investigated using a linear coordinate transformation method. Distinguishing it from previously designed illusion devices, we construct a shift-illusion device featuring resizing and rotating for both active and passive scatterers, in case the shifting region and physical space shared the same origin point. Similarly, when the shifting region is foreign to the designed device, the proposed illusion design performs as a rotation and relocation-shifting device to change the location of the scatterer. In addition, these proposed devices behave like the stealth effect in the absence of any scatterer as the outer-boundary field distribution is not disturbed. Meanwhile, the proposed concept is further extended for different mapping styles to validate the shifting-illusion concept. The constitutive parameters of the proposed devices are homogeneous, which makes them more appreciable for real implementation. It is expected that the proposed design will find potential applications in illusion devices, such as object protection, camouflage, etc. [ABSTRACT FROM AUTHOR]

A new method is proposed to design gradient refractive-index metamaterial lens antennas by optimizing both the refractive-index distribution of the lens and the feed directivity. Comparing to the conventional design methods, source optimization provides a new degree of freedom to control aperture fields effectively. To demonstrate this method, two lenses with special properties based on this method are designed, to emit high-efficiency plane waves and fan-shaped beams, respectively. Both lenses have good performance and wide frequency band from 12 to 18 GHz, verifying the validity of the proposed method. The plane-wave emitting lens realized a high aperture efficiency of 75%, and the fan-beam lens achieved a high gain of 15 dB over board bandwidth. The experimental results have good agreement with the design targets and full-wave simulations. [ABSTRACT FROM AUTHOR]

A Möbius strip has an intriguing topological property in that it only has one non-orientable side. Here we propose to utilize coupled optical ring resonators (ORRs) to simulate the topological effect of Möbius strips. This scheme is based on the fact that the counter-clockwise mode in an ORR only couples to the clockwise mode of an adjacent ORR. We show that if an odd number of ORRs form a closed loop, after a round trip the handedness of the excited mode does not return to the initial one. Only after a double round trip does the mode come back to its initial state. Such a kind of Möbius-type coupling topology can be observed from the strong backward reflection in a common bus that provides the initial excitation. Eigenmodes, reflection and transmission spectra, and field distributions are calculated and analyzed. We also study the situation without Möbius-type coupling. The difference between these two categories is discussed. COMSOL simulations verify our analysis. The importance of this investigation and potential applications are briefly discussed. [ABSTRACT FROM AUTHOR]

Transformation optics (TO), based on the formally invariant property of Maxwell’s equations, has provided a powerful strategy to design anisotropic or nearly-isotropic devices, in both time-varied and static fields. In this paper, we present and investigate the negative refraction or reflection phenomena by positive-index anisotropic materials based on transformation-optics design. First, we propose and design an inhomogeneous transformed planar lens, in which we will show the negative-refraction-like properties of transformation media. Secondly, we present a homogeneous transformed lens based on linear spatial transformation, in which we will reveal the negative-reflection properties of positive transformation media. Both transformed lenses have unusual properties which are different from those in natural materials. [ABSTRACT FROM AUTHOR]

We propose open active cloaking and illusion devices for the Laplace equation. Compared with the closed configurations of active cloaking and illusion devices, we focus on improving the distribution schemes for the controlled sources, which do not have to surround the protected object strictly. Instead, the controlled sources can be placed in several small discrete clusters, and produce the desired voltages along the controlled boundary, to actively hide or disguise the protected object. Numerical simulations are performed with satisfactory results, which are further validated by experimental measurements. The open cloaking and illusion devices have many advantages over the closed configurations in various potential applications. [ABSTRACT FROM AUTHOR]

A new isotropic and homogeneous illusion device for electromagnetic waves is proposed. This single-shelled device can change the fingerprint of the covered object into another one by manipulating the scattering of the composite structure. We show that an electrically small sphere can be disguised as another small one with different electromagnetic parameters. The device can even make a dielectric sphere (electrically small) behave like a conducting one. Full-wave simulations confirm the performance of proposed illusion device. [ABSTRACT FROM AUTHOR]