Power transfer mechanism of metallic grating coupled whispering gallery microsphere resonator

The power transfer mechanism of the Fano resonance in a metallic grating coupled whispering gallery microsphere resonator is both theoretically investigated and experimentally verified. Based on temporal coupled mode theory, a two-stage cascaded scattering model is formulated to account for the power interaction of multiple resonances in the system. The modeled results show agreement with experimental measurements and are able to explain several counter-intuitive observations in the spectra. The coupling efficiency of the grating coupler is evaluated at critical coupling by approximating symmetric resonance line-shape with grating design. Based on the modeled results, it is found that the coupling efficiency can be further improved by enhancing diffraction efficiency of the first-order diffractions.