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We study linear guided waves propagating in a slab waveguide made up of a negative-refractive-index material, the so-called left-handed waveguide. We reveal that the guided waves in left-handed waveguides possess a number of peculiar properties such as the absence of the fundamental modes, mode double degeneracy, and sign-varying energy flux. In particular, we predict the guided waves with a dipole-vortex structure of their Poynting vector.

Abstract:We study experimentally the dynamic tunability and self-induced nonlinearity of split-ring resonators incorporating variable capacitance diodes. We demonstrate that the eigenfrequencies of the resonators can be tuned over a wide frequency range, and significantly, we show that the self-induced nonlinear effects observed in the varactor-loaded split-ring resonator structures can appear at relatively low power levels.

The study of advanced artificial electromagnetic materials, known as metamaterials, provides a link from material science to theoretical and applied electrodynamics, as well as to electrical engineering. Being initially intended mainly to achieve negative refraction, the concept of metamaterials quickly covered a much broader range of applications, from microwaves to optics and even acoustics. In particular, nonlinear metamaterials established a new research direction giving rise to fruitful ideas for tunable and active artificial materials. Here we introduce the concept of magnetoelastic metamaterials, where a new type of nonlinear response emerges from mutual interaction. This is achieved by providing a mechanical degree of freedom so that the electromagnetic interaction in the metamaterial lattice is coupled to elastic interaction. This enables the electromagnetically induced forces to change the metamaterial structure, dynamically tuning its effective properties. This concept leads to a new generation of metamaterials, and can be compared to such fundamental concepts of modern physics as optomechanics of photonic structures or magnetoelasticity in magnetic materials.

Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying meta-device which performs frequency conversion, can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both electric and magnetic meta-atoms with independently controlled modulation, and the phase of this modulation is imprinted on the scattered parametric waves, controlling their shapes and directions. We develop a theory which shows how the scattering directionality, phase and conversion efficiency of sidebands can be manipulated almost arbitrarily. We demonstrate novel effects including all-angle beam steering and frequency-multiplexed functionalities at microwave frequencies around 4 GHz, using varactor diodes as tunable elements. We believe that the concept can be extended to other frequency bands, enabling metasurfaces with arbitrary phase pattern that can be dynamically tuned over the complete 2π range. arXiv:1807.08873v3 [physics.app-ph] 2 Dec 2018 AUTHOR CONTRIBUTION M. Liu conceived the idea, performed the theoretical, numerical and experimental studies, with support from

We study, analytically and numerically, reflection and transmission of an arbitrarily polarized vortex beam on an interface separating two dielectric media and derive general expressions for linear and angular Goos-Hänchen and Imbert-Fedorov shifts. We predict a novel vortex-induced Goos-Hänchen shift, and also reveal direct connection between the spin-induced angular shifts and the vortex-induced linear shifts. [3,4] shifts, which displace the output beams within and across the propagation plane, respectively (see Fig. 1). While the GH shift was explained and calculated soon after its discovery [2], the transverse IF shift was associated by significant controversies over about 50 years. The direct calculation of the IF effect was first performed for the reflected beam [5][6][7] and later generalized to the transmitted beam [8,9]. It was shown that the IF shift is closely related to the spin angular momentum carried by a polarized beam and conservation of the total angular momentum in the system [10,11] (see also [12][13][14]). Despite long history of the theoretical studies and experiments [4,15,16], analytical expression for the IF shift of a polarized Gaussian beam was derived in the correct form only recently [13,14], and these results have been confirmed both experimentally [17] and theoretically [18].In addition to the usual linear shifts, angular GH and IF shifts caused by the beam diffraction have been described [14,18]. Recently, this description of the IF effect has been extended to the case of higher-order vortex beams carrying intrinsic orbital angular momentum [19]. The vortex-induced IF shift is proportional to the vortex charge, but it also significantly depends on the beam polarization. Such IF shift was calculated [19] and measured experimentally [20] for p and s polarizations only, when the spin IF effect vanishes.The main purpose of this Letter is twofold. First, we derive explicit analytical expressions for both linear and angular IF and GH shifts in the most general case of an arbitrarily polarized vortex beam. We unveil a direct relation between the vortex-dependent IF shift and the We consider the reflection and refraction of an optical beam at an interface separating two media, as shown in Fig. 1. In addition to the coordinate system (x, y, z) attached to the interface, we employ the coordinate systems of individual beams (X a , Y a , Z a ), where a = i, r, t denotes incident, reflected and transmitted beams, respectively. The Z a axis attached to the directions of the a-th beam as determined by the Snell's law. The incident beam propagates in the (x, z) plane, so that Y a = y (see Fig. 1). We also define the wave number in the first medium, k, the angle of incidence, θ, the angle of refraction, θ ′ = sin −1 (n −1 sin θ), as well as the relative permittivity ε, permeability µ, and refractive index n = √ εµ of the second medium.We assume that the incident beam is a uniformly polarized Laguerre-Gaussian beam with the waist located at the interface, so that the transverse (X i , Y i )-compo...

Metamaterial absorbers consisting of metal, metal-dielectric, or dielectric materials have been realized across much of the electromagnetic spectrum and have demonstrated novel properties and applications. However, most absorbers utilize metals and thus are limited in applicability due to their low melting point, high Ohmic loss and high thermal conductivity. Other approaches rely on large dielectric structures and / or a supporting dielectric substrate as a loss mechanism, thereby realizing large absorption volumes. Here we present a terahertz (THz) all dielectric metasurface absorber based on hybrid dielectric waveguide resonances. We tune the metasurface geometry in order to overlap electric and magnetic dipole resonances at the same frequency, thus achieving an experimental absorption of 97.5%. A simulated dielectric metasurface achieves a total absorption coefficient enhancement factor of FT=140, with a small absorption volume. Our experimental results are well described by theory and simulations and not limited to the THz range, but may be extended to microwave, infrared and optical frequencies. The concept of an all-dielectric metasurface absorber offers a new route for control of the emission and absorption of electromagnetic radiation from surfaces with potential applications in energy harvesting, imaging, and sensing.

We suggest a new class of hyperbolic metamaterials for THz frequencies based on multilayer graphene structures. We calculate the dielectric permittivity tensor of the effective nonlocal medium with a periodic stack of graphene layers and demonstrate that tuning from elliptic to hyperbolic dispersion can be achieved with an external gate voltage. We reveal that such graphene structures can demonstrate a giant Purcell effect that can be used for boosting the THz emission in semiconductor devices. Tunability of these structures can be enhanced further with an external magnetic field which leads to the unconventional hybridization of the TE and TM polarized waves.PACS numbers: 78.67.Bf, 73.20.Mf A hyperbolic medium is a special class of indefinite media [1] described by the diagonal permittivity tensor with the principal components being of the opposite signs which results in a hyperbolic shape of the isofrequency contours [2,3]. Such media have a number of unique properties including negative refraction [1,4] and subwavelength imaging [5]. One of the possible realizations of hyperbolic media is a periodic metal-dielectric nanostructured metamaterial where the hyperbolic nature of the isofrequency curves appears due to the excitation of the near-field plasmon Bloch waves [6,7]. Hyperbolic metamaterials have been realized for optical, infrared, and microwave frequency ranges. Realization of the THz hyperbolic media could allow to boost otherwise slow THz radiative transitions in semiconductor devices which would lead to the development of a new class of THz sources.Graphene, a two-dimensional lattice of carbon atoms, exhibits a wide range of unique properties [8][9][10]. Surface plasmons excited in individual graphene sheets have been extensively studied, both theoretically [11][12][13][14][15][16][17] and experimentally [18,19].In this Letter, we suggest a novel class of hyperbolic metamaterials where individual graphene sheets are separated by host dielectric slabs, as shown schematically in Fig. 1. It is easy to notice an analogy between a graphene sheet placed inside a dielectric medium and a thin metal waveguide imbedded into a dielectric matrix, which also supports localized surface plasmon polaritons. Assuming this analogy, we may expect that a periodic lattice of the graphene sheets may behave like an effective hyperbolic medium due to the coupling between the surface plasmons localized at the individual graphene sheets [20]. Importantly, surface plasmons in graphene have low losses and strong localization in the THz region. Indeed, as we demonstrate below, a periodic structure of graphene layers creates a novel type of metamaterial with strong nonlocal response and hyperbolic properties of its disper- sion curves for TM-polarized waves in the THz frequency range and superior characteristics such as a giant Purcell effect and tunability by a gate voltage or magnetic field.It is important to mention that the periodic layered structure shown in Fig. 1 resembles a natural graphite which is known to exhibit m...