Topologically phases, characterized by topological invariants of bulk energy bands, provide remarkable capability to robustly control the propagation of electrons, photons, and phonons. The recently reported higher-order topological insulators (HOTIs) have shown that not only surface and edge states, but also localized corner states can be topologically protected. So far, most realizations of photonic HOTIs are based on lumped circuit components or bulky structures (assume infinite height) with confining metallic plates, which are not suitable for practical integrated photonics applications. Here, we show possible HOTIs’ metasurface designs using patterned flat plasmonic sheets as well as thin slabs of all-dielectric photonic crystals based on square and kagome lattices. The structures support both gapped one-dimensional edge states and in-gap zero-dimensional corner states. The non-trivial topology of the bands is characterized by 2D Zak phase (bulk polarization) and the presence of the topological modes is determined in a dimensional hierarchy according to bulk-edge-corner correspondence. The higher-order phases can be understood as the result of the interplay of localization mechanisms along two dimensions. Topological transitions are realized by tweaking the arrangement of the constituent atoms of the unit cell, which changes the intra/inter-cell coupling strengths and the symmetry of the lattice/interface. Our work opens the door for robust localized cavity as well as guided edge modes on scalable, integrated photonic platforms, which feature improved control of light-matter interactions. Additionally, since the proposed structures are open-boundary, this allows for greater degree of flexibility and direct experimental studies of classical topological states using near-field scanning technique.

Date Published: 26 February 2020
PDF: 8 pages
Proc. SPIE 11289, Photonic and Phononic Properties of Engineered Nanostructures X, 1128909 (26 February 2020); doi: 10.1117/12.2547285

Published in SPIE Proceedings Vol. 11289:
Photonic and Phononic Properties of Engineered Nanostructures X
Ali Adibi; Shawn-Yu Lin; Axel Scherer, Editor(s)