Independent control of differently-polarized waves using anisotropic gradient-index metamaterials

Broadband birefringent metamaterial lens with bi-functional high-gain radiation and deflection properties

Birefringent metamaterial shows fantastic properties in controlling the propagation of electromagnetic wave. Based on the birefringent theory, a Ku-band birefringent metamaterial lens is proposed, which can radiate high gain TE wave with a TE wave feed and deflect incident TM wave. To realize bi-functional high gain radiation or deflection, the required permittivity distribution is analyzed first. Then, the unit cells of metamaterial lens are carefully designed based on effective permittivity equations to achieve the desired permittivity distribution. To demonstrate the present design, a cylindrical birefringent lens prototype is fabricated using 3D printing techniques. The experiments verify that, with a rectangular waveguide feeding on the lens surface or a horn antenna illuminated in the far field, the Ku-band birefringent metamaterial lens performs as a high-gain broadband radiator for the TE wave feed or a deflector for the incident TM wave.

Polarization-independent broadband meta-surface for bifunctional antenna

Functional integration is crucial and has become a research interest in recent years; however, available efforts suffer from low efficiency and narrow operating bandwidth. Here, we propose a novel strategy to design bifunctional meta-surface with high efficiency and largely enhanced bandwidth in reflection geometry. For demonstration, we designed and fabricated a bifunctional meta-surface which enables both focusing and anomalous reflection under different polarizations. The working bandwidth is significantly extended by using the dual-resonant three-turn meander-line resonator (TMLR) element which provides an almost consistent phase response within a large frequency interval. For potential applications, we engineered a bifunctional antenna by launching the designed meta-surface with proper feed sources. Numerical and experimental results coincide well, indicating bifunctionalities of high gain pencil-beam radiation (reflectarray) and beam steering radiation with comparable performances. Our results can stimulate the realizations of high-performance meta-surfaces and antenna systems.

Independent modulations of the transmission amplitudes and phases by using Huygens metasurfaces

We propose ultrathin Huygens metasurfaces to control transmission amplitudes and phases of electromagnetic waves independently, in which each unit cell is comprised of an electric dipole and a magnetic dipole. By altering the electric and magnetic responses of unit cells, arbitrary complex transmission coefficients with modulus values smaller than 0.85 are obtained. Two Huygens metasurfaces capable of controlling the diffraction orders are designed and fabricated by modulating the distributions of the complex transmission coefficients. More complicated functions such as holographic imaging can also be accomplished by using the proposed Huygens metasurfaces.

Luneburg lens with extended flat focal surface for electronic scan applications

Luneburg lens with flat focal surface has been developed to work together with planar antenna feeds for beam steering applications. According to our analysis of the conventional flattened Luneburg lens, it cannot accommodate enough feeding elements which can cover its whole scan range with half power beamwidths (HPBWs). In this paper, a novel Luneburg lens with extended flat focal surface is proposed based on the theory of Quasi-Conformal Transformation Optics (QCTO), with its beam steering features reserved. To demonstrate this design, a three-dimensional (3D) prototype of this novel extend-flattened Luneburg lens working at Ku band is fabricated based on 3D printing techniques, whose flat focal surface is attached to a 9-element microstrip antenna array to achieve different scan angles. Our measured results show that, with different antenna elements being fed, the HPBWs can cover the whole scan range.

Photonic nanojet of cylindrical metalens assembled by hexagonally arranged nanofibers for breaking the diffraction limit

We designed a novel cylindrical metalens assembled by hexagonally arranged close-contact nanofibers. A near-field focusing nanojet with a full-width at half-maximum (FWHM) waist, 26.7% smaller than the Abbe diffraction limit for 532 nm wavelength light, is observed at the bottom of a 1600 nm diameter cylindrical metalens assembled by 160 nm diameter nanofibers irradiated by a plane wave from the top. Using differently sized nanofibers as building blocks to assemble the metalens, the waist size of the produced photonic nanojet in the near-field zone and the lateral resolution of the focus can be flexibly adjusted, simultaneously breaking the diffraction limit.

A Tunable Dispersion-Free Terahertz Metadevice with Pancharatnam-Berry-Phase-Enabled Modulation and Polarization Control

It is extremely challenging to control the phase of light at will in free space. Here, Pancharatnam-Berry-phase-enabled, tunable phase control of free-space light is experimentally demonstrated in an ultrathin flexible dispersion-free metadevice. This metadevice enables the broadband conversion of linearly polarized light into any desired output polarization.