Ideal nodal rings of one-dimensional photonic crystals in the visible region

Abstract

Three-dimensional (3D) artificial metacrystals host rich topological phases, such as Weyl points, nodal rings, and 3D photonic topological insulators. These topological states enable a wide range of applications, including 3D robust waveguides, one-way fiber, and negative refraction of the surface wave. However, these carefully designed metacrystals are usually very complex, hindering their extension to nanoscale photonic systems. Here, we theoretically proposed and experimentally realized an ideal nodal ring in the visible region using a simple 1D photonic crystal. The π-Berry phase around the ring is manifested by a 2π reflection phase’s winding and the resultant drumhead surface states. By breaking the inversion symmetry, the nodal ring can be gapped and the π-Berry phase would diffuse into a toroidal-shaped Berry flux, resulting in photonic ridge states (the 3D extension of quantum valley Hall states). Our results provide a simple and feasible platform for exploring 3D topological physics and its potential applications in nanophotonics.

Three-dimensional Weyl topology in one-dimensional photonic structures

“…And the exhibited value of π for such a charge, measured experimentally in Ref. 5 with angle-resolved reflectometry (a standard technique), unmistakably shows that we are indeed dealing with a topological nodal ring (see Fig. 1b ).…”

“…b Angle-resolved reflection spectra of one of the 1D photonic structures of Ref. 5 , showing two upwards-curvy bands (highlighted with dashed blue lines) touching, thereby forming a circular ring in the 3D energy-momentum space …”

“…For instance, so far, these three-dimensional (3D) structures involved special double gyroids constructions or other intricate 3D photonic or phononic crystals, which, while suitable for fundamental and proof-of-concept studies, are not fitting for many real-world applications—particularly at visible wavelengths and for integrated nano-photonic functions. Now, writing on p. 134 of the 11th issue of Light: Science & Applications , Wei-Min Deng and Jian-Wen Dong along with colleagues, report 5 the conception and experimental demonstration of ideal (exactly circular) nodal rings in simple, one-dimensional photonic crystals in the visible regime, alleviating a significant obstacle in the potential wider deployment of Weyl topological features in optoelectronic devices.…”

“…Further, the authors of Ref. 5 did not stop there but also demonstrated the existence of unique surface states at the boundary of two 1D photonic crystals with slightly different optogeometric parameters. Because each 1D photonic crystal is topological, one may predict, by studying only its bulk properties (modes), that each one supports a wave on its surface—thereby, merging the crystals together, we expect two such edge states to exist at the crystals’ common interface.…”

“…But for now, the elegantly simple path that Ref. 5 identified for exploiting and harnessing 3D topological features in 1D structures helps to remind one the well-known excerpt that ‘ all things are difficult before they are easy .’…”