Experimental realization of photonic topological insulator in a uniaxial metacrystal waveguide

Abstract

Photonic analogue of topological insulator was recently predicted by arranging e/m (permittivity/permeability)-matched bianisotropic metamaterials into two-dimensional superlattices. However, the experimental observation of such photonic topological insulator is challenging as bianisotropic metamaterial is usually highly dispersive, so that the e/mmatching condition can only be satisfied in a narrow frequency range. Here we experimentally realize a photonic topological insulator by embedding non-bianisotropic and non-resonant metacrystal into a waveguide. The cross coupling between transverse electric and transverse magnetic modes exists in metacrystal waveguide. Using this approach, the e/m-matching condition is satisfied in a broad frequency range which facilitates experimental observation. The topologically non-trivial bandgap is confirmed by experimentally measured transmission spectra and calculated non-zero spin Chern numbers. Gapless spin-filtered edge states are demonstrated experimentally by measuring the magnitude and phase of the fields. The transport robustness of the edge states is also observed when an obstacle was introduced near the edge.

Topological photonics

“…One-way edge states of T -breaking topological phases could be used as compact optical isolators [91]. Edge states of T -invariant topological phases [11,58] do not have reflection even when the system is reciprocal, thus it might be possible that isolators are unnecessary for photonic circuits consisting of T -invariant topological phases. The realizations of practical topologically-protected unidirectional waveguides towards optical frequencies are currently the main challenge of this emerging field.…”

“…Indeed in their experimental work, Chen et al [58] relaxed the material requirements to matching the ratio of /µ. They also realized broadband effective bianisotropic response by embedding the /µ-matched materials in a metallic planar waveguide.…”

Topologically robust transport of entangled photons in a 2D photonic system

“…These systems exhibit topologically robust edge states which are protected against backscattering caused by disorder. Topological edge states have been observed in photonic systems, using coupled ring resonators [3,4] and helical waveguides [5] in the optical domain, and also using metamaterials [6][7][8][9][10] in the microwave domain. Many other interesting platforms have been proposed to realize photonic edge states [11][12][13][14][15].…”

Experimental Realization of a Reflections-Free Compact Delay Line Based on a Photonic Topological Insulator

“…Here we present the first experimental demonstration of a photonic delay line based on topologically protected surface electromagnetic waves (TPSWs) between two PTIs which are the EM counterparts of the quantum spin-Hall topological insulators in condensed matter. Unlike conventional guided EM waves that do not benefit from topological protection, TPSWs are shown to experience multiwavelength reflection-free time delays when detoured around sharply-curved paths, thus offering a unique paradigm for compact and efficient wave buffers and other devices.The existence of localized TPSWs at the PTI's 1-13 edge 6,7,10 , or at an interface between two PTIs with different electromagnetic properties 1,3,11,12,14 , holds great promise for photonic applications. Their scattering-free propagation along sharply-curved paths 14 opens exciting opportunities across the electromagnetic spectrum, including optical isolators 15,16 multiple-input multiple-output communications systems 17 , and topologically robust broadband optical buffers and time delay lines 18,19 .…”