Coupling between waveguides and microresonators: the local approach

Coupling between optical microresonators and waveguides is a critical characteristic of resonant photonic devices with complex behavior that is not well understood. However, if the characteristic variation length of the microresonator modes is much larger than the waveguide width, the coupling parameter behavior is simplified. This condition is satisfied for whispering gallery modes in an elongated bottle microresonator with nanoscale effective radius variation, when coupled to a microfiber waveguide. Here, we use such a microresonator to experimentally investigate the local coupling parameters, which are independent of the mode distribution, and establish the values and interdependencies between these coupling parameters.