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 iscompletely 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.

A microring feedback bend-based coupling resonant system is proposed and is finite difference time domain (FDTD)-simulated to generate electromagnetically-induced transparency (EIT)-like transmission and mode distribution. The coupling between the cross-section of the waveguides gives rise to EIT-like spectrum. Most of themode field energy is concentrated in the coupling region of the feedback bend. The full-width at half-maximum(FWHM) can be tuned by controlling the gap parameter between two feedback bends. The device enables integration with some photonic devices on a chip and shows great promise in applications such as fast–slow light and optical filters.