Zero-GVD slow light of coupled topological edge states in a sandwiched photonic crystal waveguide

Abstract

We propose a new scheme to realize topological photonic states with low group velocity (vg) and zero group velocity dispersion (zero-GVD) based on a sandwiched photonic crystal (PC) waveguide, which are composed of finite sized PCs with different topological phases. In our proposed sandwiched heterostructure, two coupled topological edge states (CTESs) can be found, one of which can be applied to slow light by modifying the radii of the dielectric rods. The slow light characteristics of CTES, including zero-GVD, large average group index and normalized delay-bandwidth product, are discussed in detail based on finite element method (FEM) simulation. Besides, the robustness of CTES with slow light is verified, when introducing random disorders. Time-domain simulation results demonstrate the dispersionless transport of CETS in zero-GVD region. Our findings pave a way of topological slow light, enrich the topological PC research, and have new application in optical buffers and optical delay lines.

Tunable hexagonal boron nitride topological optical delay line in the visible region

“…As a result, those designs usually have millimeter sizes and are unsuitable for on-chip integration. In contrast, the slow-light effect of photonic crystals (PCs) can achieve compact ODLs [10][11][12][13][14][15][16][17][18][19][20] for high-density integration by reducing v g , including modified PC waveguides [10] , PC coupled optical waveguides [11] based on PC cavities, and PC microrings [12] . So far, all the ODLs based on PC structures work in the telecommunication wavelength range because a complete photonic bandgap is generally required to achieve high transmission efficiency, requiring high refractive index materials (e.g., silicon).…”

“…The topological edge states of valley photonic crystals (VPCs) allow robust unidirectional transmission of circularly polarized light without backscattering introduced by structural defects [15][16][17][18][19][20][21][23][24][25][26][27][28][29] . Slow-light waveguides based on VPCs have been demonstrated in different wavelength regions, including the near-infrared (900 nm) [15][16][17][18][19] , telecommunication (1500 nm) [16] , and gigahertz regimes [19] .…”