Bianisotropic Effective Parameters of Optical Metamagnetics and Negative-Index Materials

Approaches to the adequate homogenization of optical metamaterials are becoming more and more complex, primarily due to an increased understanding of the role of asymmetric electrical and magnetic responses, in addition to the nonlocal effects of the surrounding medium, even in the simplest case of plane-wave illumination. The current trend in developing such advanced homogenization descriptions often relies on utilizing bianisotropic models as a base on top of which novel optical characterization techniques can be built. In this paper, we first briefly review general principles for developing a bianisotropic homogenization approach. Second, we present several examples validating and illustrating our approach using single-period passive and active optical metamaterials. We also show that the substrate may have a significant effect on the bianisotropic characteristics of otherwise symmetric passive and active metamaterials

The role of current loop in harmonic generation from magnetic metamaterials in two polarizations

In this paper, we investigate the role of the current loop in the generation of second and third harmonic signals from magnetic metamaterials. We will show that the fact that the current loop in the magnetic resonance acts as a source for nonlinear effects and it consists of two orthogonal parts, leads to the generation of two harmonic signals in two orthogonal polarizations

Photonic Metasurfaces for Spatiotemporal and Ultrafast Light Control

The emergence of photonic metasurfaces - planar arrays of nano-antennas - has enabled a new paradigm of light control through wave-front engineering. Space-gradient metasurfaces induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin states

All-dielectric planar chiral metasurface with gradient geometric phase

Planar optical chirality of a metasurface measures its differential response between left and right circularly polarized (CP) lights and governs the asymmetric transmission of CP lights. In 2D ultra-thin plasmonic structures the circular dichroism is limited to 25% in theory and it requires high absorption loss. Here we propose and numerically demonstrate a planar chiral all-dielectric metasurface that exhibits giant circular dichroism and transmission asymmetry over 0.8 for circularly polarized lights with negligible loss, without bringing in bianisotropy or violating reciprocity. The metasurface consists of arrays of high refractive index germanium Z-shape resonators that break the in-plane mirror symmetry and induce cross-polarization conversion. Furthermore, at the transmission peak of one handedness, the transmitted light is efficiently converted into the opposite circular polarization state, with a designated geometric phase depending on the orientation angle of the optical element. In this way, the optical component sets before and after the metasurface to filter the light of certain circular polarization states are not needed and the metasurface can function under any linear polarization, in contrast to the conventional setup for geometry phase based metasurfaces. Anomalous transmission and two-dimensional holography based on the geometric phase chiral metasurface are numerically demonstrate as proofs of concept

Gradient metasurfaces: a review of fundamentals and applications

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic

Observation of cavity structures in composite metamaterials

We investigated the cavity structure by the deformation of a unit cell of a Composite Metamaterial (CMM) structure. We considered different cavity structures with different resonance frequencies and Q-factors. We observed the Q-factor of the cavity resonance as 108 for a CMM based single cavity wherein the cavity structure is a closed ring structure. We investigated the reduced photon lifetime and observed that at the cavity resonance, the effective group velocity was reduced by a factor of 20 for a CMM based single cavity compared to the electromagnetic waves propagating in free space. Since the unit cells of metamaterials are much smaller than the operation wavelength, subwavelength localization is possible within these metamaterial cavity structures. We found that the electromagnetic field is localized into a region of/8, where is the cavity resonance wavelength. Subsequently, we brought two cavities together with an intercavity distance of two metamaterial unit cells and then investigated the transmission spectrum of CMM based interacting 2-cavity system. Finally, using the tight-binding picture we observed the normalized group velocity corresponding to the coupled cavity structure. © 2010 Society of Photo-Optical Instrumentation Engineers

Manipulating Electromagnetic Fields with Advanced Metamaterials

In almost any scientific experiment, we take into account some particular properties of materials, e.g. electromagnetic, mechanical, thermal, etc. These properties determine a majority of the physical phenomena that arise from the interaction with matter, and thus restrict potential applications of natural materials. The discovery and subsequent development of novel materials regularly boost the standards of living through new technological progress and cutting-edge research. One of the very recent and promising discoveries is related to the field of metamaterials - artificially structured media with subwavelength patterning. These artificial materials offer a unique platform with large flexibility and unusual properties for tailoring acoustic and electromagnetic waves, including novel ways for the manipulation of light. In this thesis, I employed the concept of metamaterials for both the study of new physical phenomena related to the emerging field of topological photonics and also develop innovative applications of specific metamaterials for the advancing the magnetic resonance imaging (MRI) machines. Chapter 1 provides an introduction to the field of metamaterials and their unusual properties, starting from the definition of meta-atoms and expanding to more complex structures, including one-dimensional meta-chains and metasurfaces. This is followed by an introduction to the fields of topological photonics and magnetic resonance imaging techniques. The experimental approaches based on a microwave platform are also described. Finally, the thesis motivation and structure are summarized. Chapter 2 presents experimental studies of topological features of zigzag arrays of dielectric particles. It includes the first experimental observation of the subwavelength photonic topological edge states, topological phase transition in the chains of dielectric particles, as well as, the study of the specific features of the photonic spin Hall effect mediated by the excitation of the subwavelength topological edge states. Chapter 3 describes the study of bianisotropic metasurfaces and metamaterials. The experimental designs of bianisotropic metallic and dielectric metasurfaces are presented, with a direct observation of topologically nontrivial edge states. Further, it is revealed how to couple topologically protected metasurfaces to form three-dimensional all-dielectric topologically nontrivial bianisotropic metamaterials and metacrystals. Chapter 4 focuses on the study metasurfaces based on resonant arrays of metallic wires used for advancing magnetic resonance imaging (MRI) characteristics. A new conceptual idea for the substantial enhancement of signal-to-noise ratio of a 1.5T MRI is presented. This approach is further developed and extended to ultra-high field MRI (7T) where a direct evaluation of the metasurface properties is examined during in-vivo human brain imaging. Chapter 5 summarizes the results and concludes the thesis