A resonator-waveguide coupling (RWC) system consisting of a single resonator coupled to a waveguide is traditionally referred to as "notch" filter.It is thebasic unit of complicated RWC devices.Understanding the coupling behavior of"notch" filter is of great importance from both the fundamental and thepracticat points of view.The evanescent light field leaking from the system decays exponentially with respect to the distance from the resonator/waveguide.