On-Chip Ultra-Compact Hexagonal Boron Nitride Topological Ring-Resonator in Visible Region

Ultra-compact topological ring-resonators with chirality are important devices for quantum optics. However, there are limited demonstrations of chiral resonators, especially in the visible region. We proposed a topological photonic ring-resonator based on hexagonal boron nitride (hBN) valley photonic crystal (VPC). The spin-valley locking effect in VPC allows achieving robust unidirectional transmission of edge states in the visible region (600 nm–650 nm). As a result, a high quality factor (Q factor) (679.3) with a free spectral range of 15 nm in the visible region can be achieved in a hBN all-pass notch filter (APNF) with a compact size (2.3 μm*2.0 μm). In addition, we investigated the transmission properties of hBN ring-resonators with different shapes and combinations, confirming the flexibility of designing topological ring-resonators based on this principle. This design can be readily integrated with quantum photonic chips for broad applications.