Photonic Jackiw-Rebbi states in all-dielectric structures controlled by bianisotropy

Electric and magnetic resonances of dielectric particles have recently uncovered a range of exciting applications in steering of light at the nanoscale. Breaking of particle inversion symmetry further modifies its electromagnetic response giving rise to bianisotropy known also as magneto-electric coupling. Recent studies suggest the crucial role of magneto-electric coupling in realization of photonic topological metamaterials. To further unmask this fundamental link, we design and test experimentally one-dimensional array composed of dielectric particles with overlapping electric and magnetic resonances and broken mirror symmetry. Flipping over half of the meta-atoms in the array, we observe the emergence of interface states providing photonic realization of the celebrated Jackiw-Rebbi model. We trace the origin of these states to the fact that local modification of particle bianisotropic response affects its effective coupling with the neighboring meta-atoms which provides a promising avenue to engineer topological states of light.Comment: 5 pages, 5 figure

Far-field probing of leaky topological states in all-dielectric metasurfaces

© 2018 The Author(s). Topological phase transitions in condensed matter systems give rise to exotic states of matter such as topological insulators, superconductors, and superfluids. Photonic topological systems open a whole new realm of research and technological opportunities, exhibiting a number of important distinctions from their condensed matter counterparts. Photonic modes can leak into free space, which makes it possible to probe topological photonic phases by spectroscopic means via Fano resonances. Based on this idea, we develop a technique to retrieve the topological properties of all-dielectric metasurfaces from the measured far-field scattering characteristics. Collected angle-resolved spectra provide the momentum-dependent frequencies and lifetimes of the photonic modes that enable the retrieval of the effective Hamiltonian and extraction of the topological invariant. Our results demonstrate how the topological states of open non-Hermitian systems can be explored via far-field measurements, thus paving a way to the design of metasurfaces with unique scattering characteristics controlled via topological effects

Experimental demonstration of superdirective spherical dielectric antenna

An experimental demonstration of directivities exceeding the fundamental Kildal limit, a phenomenon called superdirectivity, is provided for spherical high-index dielectric antennas with an electric dipole excitation. A directivity factor of about 10 with a total efficiency of more than 80\% for an antenna having a size of a third of the wavelength was measured. High directivities are shown to be associated with constructive interference of particular electric and magnetic modes of an open spherical resonator. Both analytic solution for a point dipole and a full-wave rigorous simulation for a realistic dipole antenna were employed for optimization and analysis, yielding an excellent agreement between experimentally measured and numerically predicted directivities. The use of high-index low-loss ceramics can significantly reduce the physical size of such antennas while maintaining their overall high radiation efficiency. Such antennas can be attractive for various high-frequency applications, such as antennas for the Internet of things, smart city systems, 5G network systems, and others. The demonstrated concept can be scaled in frequency

Mushroom High-Impedance Metasurfaces for Perfect Absorption at Two Angles of Incidence

In this letter, we study the possibility to achieve perfect absorption of TM-polarized plane electromagnetic waves for two incidence angles at the same frequency. The effect was obtained in a high-impedance surface (HIS) also called a mushroom metasurface due to a combination of two types of dissipation losses inside each unit cell of the HIS, dielectric losses, and resistance of lumped loads. The dual-angle perfect absorption is a narrowband resonance effect. It was shown analytically that one can completely suppress the reflection at two predefined angles of incidence. This result was confirmed by numerical simulations of a practical (realistic and affordable) structure.Peer reviewe

Experimental Realization of Three-Dimensional All-Dielectric Photonic Topological Insulators

Significant progress has recently been made in the study of topological states in photonic topological systems. Being motivated by the recent theoretical proposal of three-dimensional topological structures based on high-permittivity bianisotropic particles, here we verify experimentally the concept of three-dimensional all-dielectric photonic topological insulators in the microwave frequency range. We demonstrate an excitation of topological surface states in the near field as well as their impact on the far-field radiation where the propagation direction is dictated by the excitation of a particular pseudo-spin.Experimental part of this work was supported by the Russian Science Foundation (grant No. 16-19-10538). We also acknowledge partial financial support from the Australian Research Council