Transformation optics

About: Transformation optics is a research topic. Over the lifetime, 2687 publications have been published within this topic receiving 102378 citations.

Two-dimensional electromagnetic cloaks with non-conformal inner and outer boundaries.

Abstract: Transformation optics is extended to the design of two-dimensional (2D) cloaks with non-conformal inner and outer boundaries. General and explicit expressions of the transformed medium parameters are derived, which are of the utmost importance in a cloak design procedure. A 2D cloak with irregular and non-conformal boundaries is designed as an example. Full-wave simulations combined with Huygens' Principle are applied to verify the invisibility of the cloak to external incident waves. All the theoretical and numerical results verify the effectiveness of the proposed method. The generalization in this Paper highly improves the flexibilities for cloak design.

Auxetic-like metamaterials as novel earthquake protections

Abstract: We propose that wave propagation through a class of mechanical metamaterials opens unprecedented avenues in seismic wave protection based on spectral properties of auxetic-like metamaterials. The elastic parameters of these metamaterials like the bulk and shear moduli, the mass density, and even the Poisson ratio, can exhibit negative values in elastic stop bands. We show here that the propagation of seismic waves with frequencies ranging from 1 Hz to 40 Hz can be influenced by a decameter scale version of auxetic-like metamaterials buried in the soil, with the combined effects of impedance mismatch, local resonances and Bragg stop bands. More precisely, we numerically examine and illustrate the markedly different behaviors between the propagation of seismic waves through a homogeneous isotropic elastic medium (concrete) and an auxetic-like metamaterial plate consisting of 43 cells (40 m × 40 m × 40 m), utilized here as a foundation of a building one would like to protect from seismic site effects. This novel class of seismic metamaterials opens band gaps at frequencies compatible with seismic waves when they are designed appropriately, what makes them interesting candidates for seismic isolation structures.

Bi-anisotropic Metamaterials Effective Constitutive Parameters Extraction Using Oblique Incidence S-Parameters Method

Abstract: The S-parameters method for bi-anisotropic metamaterials effective constitutive parameters extraction is extended to oblique incidence. The proposed method enables to extract all unknown parameters using S-parameters measured over a single metamaterial slab. The bi-anisotropic metamaterial is a pseudochiral omega medium and assumed to have diagonal permittivity and permeability tensors. The extraction process suggested involves both analytical extraction equations and numerical optimization. This method is utilized to show the limited validity of the assumption of absence of spatial dispersion on which the proposed approach is based. The extraction method is demonstrated over bulk and artificial media such as SRR metamaterial and the results are validated with satisfactory agreement published data in the literature.

Optical Fourier surfaces

Abstract: Gratings and holograms are patterned surfaces that tailor optical signals by diffraction. Despite their long history, variants with remarkable functionalities continue to be discovered. Further advances could exploit Fourier optics, which specifies the surface pattern that generates a desired diffracted output through its Fourier transform. To shape the optical wavefront, the ideal surface profile should contain a precise sum of sinusoidal waves, each with a well-defined amplitude, spatial frequency, and phase. However, because fabrication techniques typically yield profiles with at most a few depth levels, complex 'wavy' surfaces cannot be obtained, limiting the straightforward mathematical design and implementation of sophisticated diffractive optics. Here we present a simple yet powerful approach to eliminate this design-fabrication mismatch by demonstrating optical surfaces that contain an arbitrary number of specified sinusoids. We combine thermal scanning-probe lithography and templating to create periodic and aperiodic surface patterns with continuous depth control and sub-wavelength spatial resolution. Multicomponent linear gratings allow precise manipulation of electromagnetic signals through Fourier-spectrum engineering. Consequently, we immediately resolve an important problem in photonics by creating a single-layer grating that simultaneously couples red, green, and blue light at the same angle of incidence. More broadly, we analytically design and accurately replicate intricate two-dimensional moir\'e patterns, quasicrystals, and holograms, demonstrating a variety of previously impossible diffractive surfaces. Therefore, this approach provides instant benefit for optical devices (biosensors, lasers, metasurfaces, and modulators) and emerging topics in photonics (topological structures, transformation optics, and valleytronics).

Surface Wave Cloak from Graded Refractive Index Nanocomposites.

Abstract: Recently, a great deal of interest has been re-emerged on the possibility to manipulate surface waves, in particular, towards the THz and optical regime. Both concepts of Transformation Optics (TO) and metamaterials have been regarded as one of key enablers for such applications in applied electromagnetics. In this paper, we experimentally demonstrate for the first time a dielectric surface wave cloak from engineered gradient index materials to illustrate the possibility of using nanocomposites to control surface wave propagation through advanced additive manufacturing. The device is designed analytically and validated through numerical simulations and measurements, showing good agreement and performance as an effective surface wave cloak. The underlying design approach has much wider applications, which span from microwave to optics for the control of surface plasmon polaritons (SPPs) and radiation of nanoantennas.