Enhanced nonlinear optical responses of graphene in multi-frequency topological edge modes

Switching between topological edge states in plasmonic systems using phase-change materials

We introduce non-Hermitian plasmonic waveguide-cavity structures based on the Aubry-Andre-Harper model to realize switching between right and left topological edge states (TESs) using the phase-change material Ge₂Sb₂Te₅ (GST). We show that switching between the crystalline and amorphous phases of GST leads to a shift of the dispersion relation of the optimized structure so that a right TES for the crystalline phase, and a left TES for the amorphous phase occur at the same frequency. Thus, we realize switching between right and left TESs at that frequency by switching between the crystalline and amorphous phases of GST. Our results could be potentially important for developing compact reconfigurable topological photonic devices.

Coupled topological edge states in one-dimensional all-dielectric heterostructures

We theoretically propose a coupled-topological-edge-state waveguide (CTESW), which is composed of stacked binary one-dimensional (1D) photonic crystals with opposite topological properties. The CTESW modes originate from the coupling between a sequence of topological edge states (TESs), which can be verified by the coupled mode theory (CMT). Based on finite element method (FEM), the tunable multiple transmission peaks due to CTESW modes are obtained, and the optical properties of the system can be modulated by the geometric parameters. Besides, the CTESW modes can also be tuned by changing incident angle from 0° to 60° under TE and TM polarization. Moreover, considering the relationship between channel spacing and the frequency spectrum utilization, a dense wavelength division multiplex (DWDM) filter with 50 GHz channel spacing based on CTESW is designed in communication band.

Recent advances in 2D, 3D and higher-order topological photonics

Over the past decade, topology has emerged as a major branch in broad areas of physics, from atomic lattices to condensed matter. In particular, topology has received significant attention in photonics because light waves can serve as a platform to investigate nontrivial bulk and edge physics with the aid of carefully engineered photonic crystals and metamaterials. Simultaneously, photonics provides enriched physics that arises from spin-1 vectorial electromagnetic fields. Here, we review recent progress in the growing field of topological photonics in three parts. The first part is dedicated to the basics of topological band theory and introduces various two-dimensional topological phases. The second part reviews three-dimensional topological phases and numerous approaches to achieve them in photonics. Last, we present recently emerging fields in topological photonics that have not yet been reviewed. This part includes topological degeneracies in nonzero dimensions, unidirectional Maxwellian spin waves, higher-order photonic topological phases, and stacking of photonic crystals to attain layer pseudospin. In addition to the various approaches for realizing photonic topological phases, we also discuss the interaction between light and topological matter and the efforts towards practical applications of topological photonics.