Boundary configured chiral edge states in valley topological photonic crystal

Robust terahertz on-chip topological pathway with single-mode and linear dispersion

Terahertz on-chip pathway is crucial for next-generation wireless communication, terahertz integrated circuits, and high-speed chip interconnections, yet its development is impeded by issues like channel crosstalk and disordered scattering. In this study, we propose and experimentally demonstrate a terahertz on-chip topological pathway that exhibits exceptional transmission robustness, unaffected by structural curvature. The pathway is constructed using a subwavelength structure that combines the benefits of topological properties, such as broadband single-mode transmission and linear dispersion, with the field localization effects of periodic metal structures. By integrating topological protection into radio frequency circuits through metal microstructures, the device maintains efficient terahertz wave transmission even in the presence of scattering or structural defects while minimizing signal interference. These findings hold significant potential for applications in radio frequency device transmission and chip interconnection, particularly within the terahertz frequency range.

Reconfigurable topological wave routing based on tunable valley kink states and valley-polarized chiral edge states

Valley kink states and valley-polarized chiral edge states, whose topologically protected one-way propagation property provides a promising solution for manipulating light waves, have recently attracted considerable attention in topological photonics. However, it remains a great challenge to realize flexibly tunable dispersion for two different topological states and to develop a dynamically controllable topological photonic platform for switching topological wave routing. In this work, we propose a reconfigurable topological wave routing structure in the telecommunication frequency range, where phase-change material Sb2S3 cylinders with tunable refractive index are embedded into each topological channel to dynamically tune the dispersion of topological edge states. Via switching the phase states of Sb2S3 between amorphous and crystalline, we numerically demonstrate some unique applications of the proposed topological photonic crystals, such as topological optical switches, dual-channel selective transport, and controllable multi-channel intersection waveguides. More importantly, by digitally encoding each waveguide channel without the requirement of controlling each unit cell in the bulk domain, the proposed topological photonic platform provides a convenient and easy-to-implement solution for achieving dynamically reconfigurable topological wave routing propagation. Besides, the unique features of immunity against bending interface with disorders demonstrate the robustness of the topological wave propagation. Our proposed topological photonic platform has potential applications for designing intelligent photonic devices and opens up an avenue for advanced integrated photonic systems with reconfigurability.

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.