  A topologically protected ring-resonator formed in valley photonic crystals
is proposed and fabricated on a silicon slab. The unidirectional transmission
and robustness against structure defects of its resonant modes are illustrated.
Coupled with topological waveguides, the topological ring is functioned as
notch and channel-drop filters. The work opens up a new avenue for developing
advanced chip-integrated photonic circuits with attributes of topological
photonics.
