Directly patterned substrate-free plasmonic 'nanograter' structures with unusual Fano resonances

The application of three-dimensional (3D) plasmonic nanostructures as metamaterials,nano-antennas, and other devices faces challenges in producing metallic nanostructures with easily definable orientations, sophisticated shapes and smooth surfaces that are operational in the optical regime and beyond. Here, we demonstrate that complex 3D nanostructures can be readily achieved with focused-ion-beam irradiation-induced folding and examine the optical characteristics of plasmonic “nanograter” structures that are composed of free-standing Au films.These 3D nanostructures exhibit interesting 3D hybridization in current flows and exhibit unusual and well-scalable Fano resonances at wavelengths ranging from 1.6 to 6.4 μm. Upon the introduction of liquids of various refractive indices to the structures, a strong dependence of the Fano resonance is observed, with spectral sensitivities of 1400 nm and 2,040 nm per refractive-index-unit (RIU) under figures of merit of 35.0 and 12.5, respectively, for low-order and high-order resonance in the near-infrared region. This work indicates the exciting, increasing relevance of similarly constructed 3D free standing nanostructures in the research and development of photonics and metamaterials

Mapping inter-element coupling in metamaterials: Scaling down to infrared

The coupling between arbitrarily positioned and oriented split ring resonators is investigated up to THz frequencies. Two different analytical approaches are used, one based on circuits and the other on field quantities that includes retardation. These are supplemented by numerical simulations and experiments in the GHz range, and by simulations in the THz range. The field approach makes it possible to determine separately the electric and magnetic coupling coefficients which, depending on orientation, may reinforce or may cancel each other. Maps of coupling are produced for arbitrary orientations of two co-planar split rings resonant at around 2 GHz and then with the geometry scaled down to be resonant at around 100 THz. We prove that the inertia of electrons at high frequencies results in a dramatic change in the maps of coupling, due to reduction of the magnetic contribution. Our approach could facilitate the design of metamaterials in a wide frequency range up to the saturation of the resonant frequency

Surface waves at an interface of two metamaterial structures with interelement coupling

A configuration of two strongly coupled homogeneous two-dimensional metamaterial lattices of resonant elements is shown to be able to propagate surface magnetoinductive waves along the interface by virtue of coupling between the elements at the boundary. A study of the dispersion equations reveals the existence of two separate pass bands for surface waves which may partly overlap with pass bands supporting bulk waves. Experiments are reported on a structure consisting of 90 magnetically coupled capacitively loaded resonant rings designed to operate around 55 MHz. The measured current distributions and dispersion curves extracted from the experimental data are compared both with numerical simulations, using the generalized Kirchhoff's equation and with analytical expressions derived on the assumption of nearest-neighbor interaction. Excellent agreement between the three approaches is found. Considering that surface waves of various kinds have found a wide range of applications in the past, it is envisaged that this surface wave will open up fresh possibilities. A number of examples are presented. It is conjectured that other existing metamaterial structures might also be suitable candidates for propagating analogous surface waves. © 2010 The American Physical Society

Dimer and polymer metamaterials with alternating electric and magnetic coupling

Diatomic metamaterials, whose properties can be easily tailored, are studied with the aid of split ring resonator elements. Two different types are shown to exist depending on the coupling within a unit cell being larger or smaller than that between the unit cells. The freedom to adjust the coupling coefficients is used to construct a chain in which coupling alternates between electric and magnetic, between positive and negative. The resulting dispersion characteristics are shown to be radically different from the classical acoustic and optical branches: the upper branch is a forward wave and the lower branch is a backward wave, and even the gap between the two pass bands may disappear yielding infinite phase, finite group-velocity wave. The theory is confirmed both by simulations and experiments. © 2011 American Physical Society

Interacting waves on chains of split-ring resonators in the presence of retardation

Wave propagation is studied experimentally in a one-dimensional periodic chain of magnetically coupled split-ring resonators with a spacing of about one tenth of the resonant wavelength. Retardation leads to a strong interaction between magnetoinductive and free-space waves. Two kinds of guided modes are observed: a slow backward wave which propagates far outside the light cone, and a fast forward wave close to the light cone. The two merge in a region of zero group velocity. The results are relevant for all one- and two-dimensional periodic systems interacting with waves of the surrounding space. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3462314

Coupling mechanisms for split ring resonators: Theory and experiment

We study experimentally and theoretically coupling mechanisms between metamaterial elements of the split ring resonator (SRR) type. We show that, depending on the orientation of the elements relative to each other, the coupling may be either of magnetic or electric type or a combination of both. Experimental results on SRRs with resonances around 1.7 -1.9 GHz agree quantitatively with results of simulations (CST Microwave Studio). Further simulations provide analysis for a variety of SRRs both in the GHz and in the 20 THz frequency regions. The variety of coupling mechanisms can be employed in designing near field manipulating devices based on propagation of slow waves. © 2007 WILEY-VCH Verlag GmbH and Co. KGaA

Coupling mechanisms for split ring resonators: Theory and experiment

We study experimentally and theoretically coupling mechanisms between metamaterial elements of the split ring resonator (SRR) type. We show that, depending on the orientation of the elements relative to each other, the coupling may be either of magnetic or electric type or a combination of both. Experimental results on SRRs with resonances around 1.7 -1.9 GHz agree quantitatively with results of simulations (CST Microwave Studio). Further simulations provide analysis for a variety of SRRs both in the GHz and in the 20 THz frequency regions. The variety of coupling mechanisms can be employed in designing near field manipulating devices based on propagation of slow waves. © 2007 WILEY-VCH Verlag GmbH and Co. KGaA