Design of an ultrathin broadband transparent and high-conductive screen using plasmonic nanostructures.

In this Letter, we present a new type of ultrathin antireflection transparent and high-conductive screen based on plasmonic nanostructures that does not suffer from high loss and thickness coating and also can be used as good conductive material due to super electrical conductivity of the component (noble metal). Low reflection and greatly enhanced transmissions over a broad spectral range are observed at optical telecommunication frequencies in arbitrary polarizations. The performance is almost insensitive of the angle of incidence.

Gain-assisted transformation optics.

Loss severely degrades the cloaking effect of the device designed by traditional transformation. In this letter, we propose gain-assisted transformation optics to overcome the loss problem by introducing gain media into a spherical cloak. The gain media, which can amplify the electromagnetic fields, is controlled precisely to compensate the inherent loss in experimental realization of cloaks. We discuss the significance of controlling embedded gain materials in the context of the inverse design mechanism, which allows us to wisely select realizable materials with constant gain and loss along the radius. For practical realizations, isotropic spherical gain-assisted cloak is designed. Full-wave simulations validate the proposed design concept, which can be utilized to alleviate the inevitable loss problem in transformational optical devices.

Homogeneous and isotropic bends to tunnel waves through multiple different/equal waveguides along arbitrary directions.

We propose a novel optical transformation to design homogeneous isotropic bends connecting multiple waveguides of different cross sections which can ideally tunnel the wave along any directions through multiple waveguides. First, the general expressions of homogeneous and anisotropic parameters in the bend region are derived. Second, the anisotropic material can be replaced by only two kinds of isotropic materials and they can be easily arranged in planarly stratified configuration. Finally, an arbitrary bender with homogeneous and isotropic materials is constructed, which can bend electromagnetic wave to any desired directions. To achieve the utmost aim, an advanced method is proposed to design nonmagnetic, isotropic and homogeneous bends that can bend waves along arbitrary directions. More importantly, all of the proposed bender has compact shape due to all flat boundaries, while the wave can still be perfectly tunneled without mode distortion. Numerical results validate these functionalities, which make the bend much easier in fabrication and application.

Scattering by rotationally symmetric anisotropic spheres: potential formulation and parametric studies.

Vector potential formulation and parametric studies of electromagnetic scattering problems of a sphere characterized by the rotationally symmetric anisotropy are studied. Both epsilon and mu tensors are considered herein, and four elementary parameters are utilized to specify the material properties in the structure. The field representations can be obtained in terms of two potentials, and both TE (TM) modes (with respect to r) inside (outside) the sphere can be derived and expressed in terms of a series of fractional-order (in a real or complex number) Ricatti-Bessel functions. The effects due to either electric anisotropy ratio (Ae=epsilont/epsilonr) or magnetic anisotropy ratio (Am=mut/mur) on the radar cross section (RCS) are considered, and the hybrid effects due to both Ae and Am are also examined extensively. It is found that the material anisotropy affects significantly the scattering behaviors of three-dimensional dielectric objects. For absorbing spheres, however, the Ae or Am no longer plays a significant role as in lossless dielectric spheres and the anisotropic dependence of RCS values is found to be predictable. The hybrid effects of Ae and Am are considered for absorbing spheres as well, but it is found that the RCS can be greatly reduced by controlling the material parameters. Details of the theoretical treatment and numerical results are presented.

Anomalous behavior of nearly-entire visible band manipulated with degenerated image dipole array.

Recently, the control of anomalous light bending via flat gradient-phase metasurfaces has enabled many unprecedented applications. However, either low manipulation efficiency or challenging difficulties in fabrication hinders their practical applications, in particular in the visible range. Therefore, a concept of degenerated image dipole array is reported to realize anomalous light bending with high efficiency. A continuous phase delay varying rather than a discrete one, along with an in-plane wave vector is utilized to achieve anomalous light bending, by controlling and manipulating the mutual coupling between dipole array and the dipole array of its image. The anomalous light bending covers almost the entire visible range with broad incident angles, accompanied with preserved well-defined planar wavefront. In addition, this design is feasible to be fabricated with recent nanofabrication techniques due to its planarized surface configuration. The concept of imperfect image dipole array degenerated from ideal metamaterial absorbers surprisingly empowers significant enhancement in light manipulation efficiency for visible light in a distinct fashion.

Theoretical realization of robust broadband transparency in ultrathin seamless nanostructures by dual blackbodies for near infrared light.

We propose a counter-intuitive mechanism of constructing an ultrathin broadband transparent device with two perfect blackbodies. By introducing hybridization of plasmon modes, resonant modes with different symmetries coexist in this system. A broadband transmission spectrum in the near infrared regime is achieved through controlling their coupling strengths, which is governed by the thickness of high refractive index layer. Meanwhile, the transparency bandwidth is found to be tunable in a large range by varying the geometric dimension. More significantly, from the point view of applications, the proposed method of achieving broadband transparency can perfectly tolerate the misalignment and asymmetry of periodic nanoparticles on the top and bottom, which is empowered by the unique dual of coupling-in and coupling-out processes within the pair of blackbodies. Moreover, roughness has little influence on its transmission performance. According to the coupled mode theory, the distinguished transmittance performance is physically interpreted by the radiative decay rate of the entire system. In addition to the feature of uniquely robust broadband transparency, such a ultrathin seamless nanostructure (in the presence of a uniform silver layer) also provides polarization-independent and angle-independent operations. Therefore, it may power up a wide spectrum of exciting applications in thin film protection, touch screen techniques, absorber-emitter transformation, etc.

Transparent uniaxial anisotropic spherical particles designed using radial anisotropy.

Based on Mie scattering theory and the assumption that the particle is electrically small in size (k(t)a≪1,k(m)a≪1), an analytic relationship between radial and tangential permittivity parameters has been established for achieving minimal scattering from an arbitrary rotationally uniaxial anisotropic spherical object incident by a plane wave. Analysis of fields in both the far- and near-field zones indicates that the derived relation is not only valid for electrically small particles, but also applicable to larger ones whose sizes are comparable with the free space wavelength after slight adjustments in parameters. Furthermore, it is observed that the dielectric spherical particle of reduced tangential permittivity yields better transparency performance than the design using a plasmonic cover by Alu and Engheta [Phys. Rev. E 72, 016623 (2005)]. As such, particles with carefully engineered radial anisotropy are transparent without using any coating and are ideal for applications with space constraint and stringent transparency criteria.