We show that coupling among multiple resonances can be conveniently introduced and controlled by boundary wave scattering. This is demonstrated in optical microcavities of quasicircular shapes, where the couplings of multiple modes are determined by the scattering from harmonic boundary deformations. We analyze these couplings using a perturbation theory, which gives an intuitive understanding of the lowest-order and higher-order scattering processes. Different scattering paths between two boundary waves can either enhance or reduce their coupling strength. The effect of controlled multimode coupling is most pronounced in the direction of output from an open cavity, as the coupling can cause a dramatic change of the external cavity field distribution.

• Received 24 May 2013

DOI:https://doi.org/10.1103/PhysRevA.88.043801