Energy Transfer to Optical Microcavities With Waveguides

Micro/nanoscale radiation energy transfer is investigated in optical microcavity and waveguide coupling structures working on whispering-gallery mode optical resonances. The finite element method is employed for solving the Helmholtz equations that govern the energy transfer and time-harmonics electromagnetic (EM) wave propagation. The maximum element size concept is introduced for the numerically sensitive subdomains where local mesh refining is needed because of the presence of intensified EM fields. The results show that the energy storage capability of a resonant microcavity is predominantly determined by the cavity size. The stored energy in the $10μm$ diameter microcavity considered is several orders of magnitude larger than that in the $2μm$ diameter microcavity. The gap between a microcavity and its light-delivery waveguide has a substantial effect on the energy coupling from the waveguide to the microcavity and consequently influences significantly energy storage in the microcavity. An optimal gap is found for maximum energy storage and most efficient energy coupling. This optimal gap dimension depends not only on the configurations of the microcavity and waveguide, but also on the resonance wavelength. With increasing gap the quality factor increases exponentially and quickly saturates as the gap approaches to one wavelength involved. The submicron/nanoscale gap is crucial for generating quality resonances as well as for efficient energy transfer and coupling.