Weak coupling strength measurement between two whispering-gallery-mode microresonators near an exceptional point

Sensing is one of the important applications of the whispering-gallery-mode (WGM) microresonator. Here we consider a model consisting of two WGM microresonators and one fiber waveguide. We show that the system can be near an exceptional point when the two tapers in the fiber waveguide are coupled to the two microresonators in a way that can lead to an unidirectional coupling. We propose a method to measure the weak coupling strength between the two microresonators. Compared to the conventional method, our method operates near an exceptional point and has the ability to measure smaller coupling strength.