Hai-Xiao Wang

Crystalline symmetry offers a powerful tool to realize photonic topological phases, in which additional trivial claddings are typically required to confine topological boundary states. However, the utility of the trivial cladding in manipulating topological waves is often overlooked. Here, we demonstrate two topologically distinct kagome photonic crystals (KPCs) based on different crystalline symmetries: ‐symmetric KPCs exhibit a quantum spin Hall phase, while ‐symmetric KPCs serve as trivial cladding. By tuning the geometric parameter of the trivial cladding, we observe that a pair of topological interface states featured with pseudospin‐momentum locking undergoes a phase transition, accompanied by the appearance and disappearance of corner states in a finite hexagonal supercell. Such a geometry‐induced band inversion is characterized by a sign change in the Dirac mass of the topological interface states and holds potential for applications such as rainbow trapping. Furthermore, we experimentally demonstrate that the corner states, which are a hallmark of higher‐order topology, also depend critically on the trivial cladding. Our work highlights the crucial role of trivial claddings on the formation of topological boundary states, and offers a novel approach for their manipulation.

Antichiral surface states, characterized by unidirectional propagation on parallel surfaces, offer unique potential for controlling classical waves. However, their realization typically relies on complex implementations of the two-dimensional modified Haldane model, limiting practical applications. Here, we propose a simplified scheme to realize such states within the nodal-line semimetal phase of a single-layer honeycomb lattice, by emulating the essential physics of the modified Haldane model through an introduced layer degree of freedom. Furthermore, we demonstrate that unequal vertical interlayer couplings can generate valley higher-order topological partial bandgaps, hosting coexisting one-dimensional hinge states and gapped antichiral surface states. We numerically verify these multiple topological states in acoustic crystals, establishing a versatile platform for advanced wave manipulation.

Crystalline symmetry offers a powerful tool to realize photonic topological phases, in which additional trivial claddings are typically required to confine topological boundary states. However, the utility of the trivial cladding in manipulating topological waves is often overlooked. Here, we demonstrate two topologically distinct kagome photonic crystals (KPCs) based on different crystalline symmetries: \mathbit{C}_\mathbf{6}- symmetric KPCs exhibit a quantum spin Hall phase, while \mathbit{C}_\mathbf{3}-symmetric KPCs serve as trivial cladding. By tuning the geometric parameter of the trivial cladding, we observe that a pair of topological interface states featured with pseudospin-momentum locking undergoes a phase transition, accompanied by the appearance and disappearance of corner states in a finite hexagonal supercell. Such a geometry-induced band inversion is characterized by a sign change in the Dirac mass of the topological interface states and holds potential for applications such as rainbow trapping. Furthermore, we experimentally demonstrate the corner states, which is a hallmark of higher-order topology, also depend critically on the trivial cladding. Our work highlights the crucial role of trivial claddings on the formation of topological boundary states, and offers a novel approach for their manipulation.

We have developed a mirrored photonic crystal interface (MPCI) by applying a mirror operator to expanded honeycomb photonic crystals (EHPCs) exhibiting nontrivial band topology. This configuration supports a pair of interface states characterized by spin-momentum locking. Notably, by adjusting the geometric parameters of the EHPCs without altering their topological properties, we observe a process where these interface states close and reopen, indicating a topological phase transition. Further analysis reveals that the MPCIs function as interfaces between EHPCs with C₆- and C₃-symmetric configurations, representing nontrivial and trivial topological phases, respectively, separated by air gaps. Our findings highlight the tunable nature of topological edge states formed by a single type of photonic crystal, which could have potential applications in robust transport devices within photonic integrated circuits.

Recent advances in topological photonics provide unprecedented opportunities to realize a photonic cavity. A recent work shows that the electromagnetic wave can be effectively trapped via the shifted photonic crystal interfaces (SPCIs), which offers an alternative approach to realizing the photonic cavity. Here, we proposed one-dimensional topological insulators based on an SPCIs-induced cavity chain, which is analogous to the Su–Schrieffer–Hegger model and is compatible with the silicon-on-insulator platform. Owing to the asymmetry feature of SPCIs-induced cavities, the topological cavity chains can be either realized by alternating the cavity modes or by tuning the distance between two cavities. The nontrivial band topology of SPCIs-induced cavity chains is further confirmed by observing topological end states, which exhibit robustness against geometrical imperfections. Our work holds promises for designing robust photonic devices, which may find potential applications in future integrated photonics.

Recent advances in all-dielectric topological photonics offer unprecedented opportunities for achieving robust waveguides. However, most topological waveguides are localized at small areas around the interfaces and usually operate in a single frequency window, leading to the low-throughput energy transmission over a narrow bandwidth. Here we report on the implementation of a dual-band topological large-area waveguide in heterostructures based on valley photonic crystals, in which the bandwidths are effectively widen by exploiting the dual-band topology. Inherited from the valley topology, the topological large-area waveguides exhibit the valley-locking effect at two separate frequency windows and are robust against sharp corners and defects. We also observe intriguing topological refractions of the topological large-area waveguides into the ambient space at zigzag and armchair terminations. Our work highlights both the tunable width and the large bandwidth of topological waveguides, paving the way for topological photonic integrated circuits with high performance and multifunctionality.