Mid-infrared topological cavity with valley edge modes

Quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) are well-established and reliable sources of mid-infrared (IR) radiation. In photonic crystals, topological edge states (ESs) emerge at the boundaries between spatial domains with different topological properties. These ESs exhibit unidirectional transmission, effectively suppressing backscattering and maintaining robustness against defects and disorders. In this work, the unique attributes of topological valley photonic crystals compatible with QCLs and ICLs are investigated. The results demonstrate the topological protection offered by valley-dependent ES, which is essential for one-way optical propagation in devices and resonant cavities. Furthermore, topologically protected triangular cavities based on VPCs exhibit high quality factors and uniform energy distribution, even in the presence of structural defects. Additionally, the different characteristics of transverse electric (TE) and transverse magnetic (TM) mode resonant cavities enable the development of application-specific topological lasers, allowing for optimal performance tailored to diverse operational requirements.