Frequency-dependent selectively oriented edge state topological transport

Valley topological photonic crystals(TPCs),which are robust against local disorders and structural defects,have attracted great research interest,from theoretical verification to technical applications.However,previous works mostly focused on the robustness of topologically protected edge states and little attention was paid to the importance of the photonic bandgaps(PBGs),which hinders the implementation of various multifrequency functional topological photonic devices.Here,by systematically studying the relationship between the degree of symmetry breaking and the working bandwidth of the edge states,we present spoof surface plasmon polariton valley TPCs with broadband edge states and engineered PBGs,where the operation frequency is easy to adjust.Furthermore,by connecting valley TPCs operating at different frequencies,a broadband multifunctional frequency-dependent topological photonic device with selectively directional light transmission is fabricated and experimentally demonstrated,achieving the functions of wavelength division multiplexing and add–drop multiplexing.We provide an effective and insightful method for building multi-frequency topological photonic devices.

Nonlinear topological valley Hall edge states arising from type-Ⅱ Dirac cones

A Dirac point is a linear band crossing point originally used to describe unusual transport properties of materials like graphene.In recent years,there has been a surge of exploration of type-II Dirac/Weyl points using various engineered platforms including photonic crystals,waveguide arrays,metasurfaces,magnetized plasma and polariton micropillars,aiming toward relativistic quantum emulation and understanding of exotic topological phenomena.Such endeavors,however,have focused mainly on linear topological states in real or synthetic Dirac/Weyl materials.We propose and demonstrate nonlinear valley Hall edge(VHE)states in laserwritten anisotropic photonic lattices hosting innately the type-Ⅱ Dirac points.These self-trapped VHE states,manifested as topological gap quasi-solitons that can move along a domain wall unidirectionally without changing their profiles,are independent of external magnetic fields or complex longitudinal modulations,and thus are superior in comparison with previously reported topological edge solitons.Our finding may provide a route for understanding nonlinear phenomena in systems with type-Ⅱ Dirac points that violate the Lorentz invariance and may bring about possibilities for subsequent technological development in light field manipulation and photonic devices.

谷边缘态作为连续域中的束缚态

Bound states in the continuum(BICs) are spatially localized states with energy embedded in the continuum spectrum of extended states. The combination of BICs physics and nontrivial band topology theory givs rise to topological BICs, which are robust against disorders and meanwhile, the merit of conventional BICs is attracting wide attention recently. Here, we report valley edge states as topological BICs, which appear at the domain wall between two distinct valley topological phases. The robustness of such BICs is demonstrated. The simulations and experiments show great agreement. Our findings of valley related topological BICs shed light on both BICs and valley physics, and may foster innovative applications of topological acoustic devices.