Efficient coupling between dielectric waveguide modes and exterior plasmon whispering gallery modes

Inefficient coupling between dielectric guided mode and plasmon mode has been overlooked in the past. The mechanism in it is essentially different from the conventional coupling between dielectric modes. Based on qualitative theoretical analysis, we proposed two methods to strengthen the coupling between dielectric waveguide modes and exterior plasmon whispering gallery modes. One is using a U-shaped bent waveguide to break the adiabatic mode conversion process, and the other is to render the dielectric mode of higher-order to reach phase matching with plasmon mode. Both the transmission spectrum of waveguide and the energy spectrum of cavity demonstrate that the coupling efficiencies can be greatly improved. These simple configurations are potential for wide applications, for example, tunable integrated optical devices, nanolasers and sensors.