Boundary configured chiral edge states in valley topological photonic crystal

Terahertz tunable band-stop filter using topological valley photonic crystals

In recent years, there has been a growing interest in the wideband propagation and control of terahertz (THz) radiation due to its potential for a variety of applications, such as 6G communication, sensing, and imaging. One promising approach in this area is the use of valley photonic crystals (VPCs), which exhibit properties like wider band gaps and robust propagation. In this paper, a two-dimensional dielectric silicon-air VPC is studied, which is constructed from a method of inversion symmetry breaking providing a band gap of 109.4 GHz at a mid-gap frequency of 0.376 THz. We employ an optimized bearded-stack interface to construct the VPC waveguide for wideband THz propagation along straight and Z-shaped paths. We demonstrate that a band-stop response can be achieved in a VPC by introducing periodic defects along the domain wall. Furthermore, the stop range can be tuned by varying the refractive index of the defects through incorporating liquid crystal along the domain wall of VPC. Our proposed structure and the techniques employed could be promising for the development of a band-stop filter (BSF) and other photonic components having potential applications in 6G communication and beyond.

Hybrid topological photonic crystals

Topologically protected photonic edge states offer unprecedented robust propagation of photons that are promising for waveguiding, lasing, and quantum information processing. Here, we report on the discovery of a class of hybrid topological photonic crystals that host simultaneously quantum anomalous Hall and valley Hall phases in different photonic band gaps. The underlying hybrid topology manifests itself in the edge channels as the coexistence of the dual-band chiral edge states and unbalanced valley Hall edge states. We experimentally realize the hybrid topological photonic crystal, unveil its unique topological transitions, and verify its unconventional dual-band gap topological edge states using pump-probe techniques. Furthermore, we demonstrate that the dual-band photonic topological edge channels can serve as frequency-multiplexing devices that function as both beam splitters and combiners. Our study unveils hybrid topological insulators as an exotic topological state of photons as well as a promising route toward future applications in topological photonics.

Non-Hermitian kagome photonic crystal with a totally topological spatial mode selection

Recently, the study of non-Hermitian topological edge and corner states in sonic crystals (SCs) and photonic crystals (PCs) has drawn much attention. In this paper, we propose a Wannier-type higher-order topological insulator (HOTI) model based on the kagome PC containing dimer units and study its non-Hermitian topological corner states. When balanced gain and loss are introduced into the dimer units with a proper parity-time symmetric setting, the system will show asymmetric Wannier bands and can support two Hermitian corner states and two pairs of complex-conjugate or pseudo complex-conjugate non-Hermitian corner states. These topological corner states are solely confined at three corners of the triangular supercell constructed by the trivial and non-trivial kagome PCs, corresponding to a topological spatial mode selection effect. As compared to the non-Hermitian quadrupole-type HOTIs, the non-Hermitian Wannier-type HOTIs can realize totally topological spatial mode selection by using much lower coefficients of gain and loss. Our results pave the way for the development of novel non-Hermitian photonic topological devices based on Wannier-type HOTIs.