Light and sound interplay in whispering gallery mode resonators

Whispering Gallery Mode Resonators (WGMRs) are robust and compact structures that confine resonant photons and phonons for extended time. This extraordinary confinement greatly enhances light and sound interactions and allows a plethora of fundamental phenomena to happen, ranging from nonlinear optics with continuous wave lasers to exceptional point going through mode shifting, splitting and broadening. These WGMR are highly versatile since their design can be tailored to the application by modifying either their size or the material used for their fabrication. We will focus on three dimensional WGMR, we will describe the physical working principles, their fabrication and their applications as sensors.