Vertically coupled microring resonator filter with multilevel crossing busline waveguide

To eliminate the scattering loss at the crossing points of busline waveguides, a multilevel crossing structure of busline waveguide was introduced into the vertically coupled microring resonator filter. The top surface of each buried waveguide was perfectly planarized by a new fabrication process and clear filter responses were observed for a single ring and a double series coupled ring resonator with multilevel crossing busline waveguides.