Tunable topological edge and corner states in an all-dielectric 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.

Design of wavelength division multiplexing devices based on tunable edge states of valley photonic crystals

Wavelength division multiplexing (WDM) devices are key photonic integrated circuit (PIC) elements. Conventional WDM devices based on silicon waveguides and photonic crystals have limited transmittance due to the high loss introduced by the strong backward scattering from defects. In addition, it is challenging to reduce the footprint of those devices. Here we theoretically demonstrate a WDM device in the telecommunication range based on all-dielectric silicon topological valley photonic crystal (VPC) structures. We tune its effective refractive index by tuning the physical parameters of the lattice in the silicon substrate, which can continuously tune the operating wavelength range of the topological edge states, which allows the designing of WDM devices with different channels. The WDM device has two channels (1475 nm-1530 nm and 1583 nm-1637 nm), with contrast ratios of 29.6 dB and 35.3 dB, respectively. We demonstrated highly efficient devices for multiplexing and demultiplexing in a WDM system. The principle of manipulating the working bandwidth of the topological edge states can be generally applied in designing different integratable photonic devices. Thus, it will find broad applications.