Multiphase Topological Laser in Double-Layer Hexagonal Photonic Crystals

Topological photonics has shown great potential in optical device design, particularly in the development of topological lasers. However, existing research primarily focuses on single topological phases, failing to fully exploit the advantages of multiple topological phases. Conventional cladding-type topological lasers require an interface between topological distinct crystals, with one acting as cladding, which reduces area efficiency. This paper explores single-mode lasing properties of a double-layer hexagonal photonic crystal structure, highlighting both the ideal quantum spin Hall (IQSH) phase and spin higher-order (SHO) phase. In the IQSH phase, the robust waveguide design eliminates the need for a cladding layer, enhancing area efficiency compared to previous models. Additionally, incorporating pendant sites further amplifies lasing intensity by flattening the band structure. In the SHO phase, boundary dispersion splits, forming corner states with antisymmetric or symmetric properties that determine the final lasing mode, providing greater tunability compared to previous higher-order topological lasers. This paper advances the theoretical understanding of nonlinear and non-Hermitian physics in topological phases and optimizes the size and power efficiency of topological lasers, paving the way for multifunctional laser devices and practical photonic applications.