Abstract: The present disclosure is directed toward photonic elements comprising rib-waveguide-based ring resonators having high coupling efficiency between their bus and ring waveguides within the coupling region of the ring resonator, as well as operability over a wide spectral range. Embodiments disclosed herein employ a small-diameter ring waveguide and a bus waveguide that collectively define an asymmetrical coupler having a coupling region at which the optical confinement of the bus waveguide is stronger on side of the bus waveguide distal to the ring waveguide than on the side of the bus waveguide that is proximal to the ring waveguide. In some embodiments, in the coupling region, the bus waveguide has ridge and an inner bus-slab portion that is shared with the ring waveguide, while the outer bus-slab portion is at least partially removed to give rise to stronger optical confinement at the outer edge of the ridge of the bus waveguide.