Optical coupling between a cavity mode and a waveguide in a two-dimensional photonic crystal

We theoretically investigate optical coupling between a waveguide and a localized mode arising in a cavity resonator of a two-dimensional photonic crystal. By carrying out two-dimensional finite-difference time-domain calculations, we evaluate coupling efficiency by observing whispering gallery mode decaying through the waveguide. Calculated coupling efficiency shows periodical change with change of waveguide width. We found that the coupling becomes strong when group velocity of the relevant waveguide mode is small. This correlation between the coupling efficiency and waveguide mode indicates that we can widely tune the coupling efficient by small change of structural parameters.

► We theoretically investigate coupling between cavity mode and waveguide.
► We found that coupling becomes strong when waveguide mode has small group velocity.
► By changing width of waveguide, we can tune strength of the coupling.