Electromagnetically-induced transparency-like transmission characteristics of a waveguide coupled to a microsphere resonator

The limitation of traditional microring mode resonance, the microsphere confocal cavity is the best candidate for a low loss and controllable linewidth. Based on the transform matrix method, we investigate the waveguide coupled to a microsphere whispering-gallery mode (WGM) system. We find that the confocal cavity mode is completely different from the traditional ring cavity mode. The confocal cavity mode is excited in asymmetrical dual microsphere systems, and the spectrum of asymmetrical dual microsphere systems appear as an electromagnetically-induced transparency (EIT)-like profile, whereas the spectrum of symmetrical dual microsphere systems appears as Lorentz profile. The traditional ring cavity mode is excited in the symmetrical single microsphere system.