Continuously tunable topological defects and topological edge states in dielectric photonic crystals

Abstract

Topological defects in solid-state materials are crystallographic imperfections that local perturbations cannot remove. Owing to their nontrivial real-space topology, topological defects such as dislocations and disclinations could trap anomalous states associated with nontrivial momentum-space topology. The real-space topology of dislocations and disclinations can be characterized by the Burgers vector B, which is usually a fixed fraction and integer of lattice constant in solid-state materials. Here we show that in a dielectric photonic crystal -an artificial crystalline structure, it is possible to tune B continuously as a function of the dielectric constant of dislocations. Through this unprecedented tunability of B, we achieve proper controls of topological interfacial states, i.e., reversal of their helicities. Based on this fact, we propose a topological optical switch controlled by the dielectric constant of the tunable dislocation. Our results shed light on the interplay of real and reciprocal space topologies and offer a new scheme to implement scalable and tunable robust topological waveguides in dielectric photonic crystals.

Polarization-independent dislocation modes in photonic crystals

“…This approach is rooted in topological pumping by changing translation parameter, which achieves the accidental degeneracy of dislocation modes of two polarizations without careful search of the anisotropic permittivity. The dislocation structures in PC exist in other lattices such as honeycomb lattice [59], and this polarization-independent dislocation modes can be realized in any lattice [25]. This work provides a topological strategy for designing polarization-independent photonic devices.…”

Simultaneous pseudospin and valley topological edge states of elastic waves in phononic crystals made of distorted Kekulé lattices

“…In recent years, the emergence of topological metamaterials has provided an abundant and efficient platform for studying robust wave propagation, which supports the topological edge states with defect immunity and backscattering suppression . By analogy with the quantum Hall effect (QHE) [21], the quantum spin Hall effect (QSHE) [22,23] or the quantum valley Hall effect (QVHE) [24,51], the concept of topological metamaterials originating from condensed matter physics [25,26] has been rapidly extended to the classical wave areas, including electromagnetic waves [8][9][10][11], acoustic waves [12][13][14][15][16][17][18][19][20] and elastic waves .…”