Visualization of topological transitions and imaging of higher-order topological states in photonic metasurfaces

Abstract

Topological photonic systems represent a new class of optical materials supporting boundary modes with unique properties, not found in conventional photonics. While the early research on topological photonics has focused on edge and surface modes in 2D and 3D systems, respectively, recently higher-order topological insulators (HOTIs) supporting lower-dimensional boundary states have been introduced. In this work we design and experimentally realize a photonic kagome metasurface exhibiting a Wannier-type higher-order topological phase. We demonstrate and visualize the emergence of a topological transition and opening of a Dirac cone by directly exciting the bulk modes of the HOTI metasurface via solid-state immersion spectroscopy. The open nature of the metasurface is then utilized to directly image topological boundary states. We show that, while the domain walls host 1D edge states, their bending induces 0D higher-order topological modes confined to the corners. The demonstrated metasurface hosting topological boundary modes of different dimensionality paves the way to a new generation of universal and resilient optical devices which can controllably scatter, trap and guide optical fields in a robust way.Introduction. Topological photonics 1, 2, 3 offers new approaches to control and manipulate electromagnetic radiation by exploiting synthetic gauge fields to imitate exotic quantum solid-state phenomena 2,

Free-Space Nonreciprocal Transmission Based on Nonlinear Coupled Fano Metasurfaces

“…We emphasize that this power level is very small, and can be achieved even with continuous wave lasers; however, this comes at the cost of being vulnerable to fabrication errors [50]. Concepts borrowed from topological photonics may be used to enhance the robustness of the response in high-quality factor systems, even in the presence of fabrication errors [51,52]. We also studied the response of this optimal device for different electrical lengths θ in Figure 8.…”

Near-field mapping of the edge mode of a topological valley slab waveguide at λ = 1.55 μ m

“…the boundary between topologically distinct domains), which is relevant to microwave near-field experiments 24,25,29,45 and far-field observations on various slab topological platforms. 27,33,35,46 Some of the incident light is coupled into the bulk VPC domains, but these mode intensities decay significantly with propagation distance, whereas the mode confined to the topological interface remains clearly visible. We observe that the waveguide mode is confined to within 1.4 um of the domain wall (Fig.…”