  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 (679.3) with a free spectral range of
15.2 nm in the visible region can be achieved in a hBN all-pass filter with a
compact size. 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.
