  We study the effect of mode-coupling on a single-photon device in which a
dipole-quantum-emitter (DQE) is embedded in a bimodal whispering-gallery-mode
cavity (WGMC). A scatterer is used to induce mode coupling between
counter-clockwise and clockwise propagating light fields, which interact with
the DQE. In contrast to models for the interaction between a DQE and a
(one-mode or two-mode) cavity field, we find that strong photon antibunching
can occur even for a weak DQE-field coupling and large dephasing of the DQE,
when mode coupling is introduced. We also find that mode coupling can make the
device robust against either the frequency mismatch between cavity modes and
the DQE or the coupling strength mismatch between the DQE and each mode in the
two-mode cavity. Moreover, we find that these mismatches can be used to
generate better antibunching in the weak DQE-field coupling regime. Our study
shows that mode coupling in a bimodal cavity is very important for the
realization of a good single-photon device.
