  We theoretically study the interaction between dual cavity modes in a planar
photonic microcavity structure in the optical communication wavelength range.
The merging and splitting of cavity mode is analyzed with realistic microcavity
structures. The merging of dual cavity resonance into a single cavity resonance
is achieved by changing the number of layers between the two cavities. The
splitting of single cavity resonance into dual cavity resonance is obtained
with an increase in the reflectivity of mirrors in the front and rear side of
the microcavity structure. The threshold condition for the merging and
splitting of cavity mode is established in terms of structural parameters. The
physical origin of the merging of dual cavity modes into a single cavity
resonance is discussed in terms of the electric field intensity distribution in
the microcavity structure. The microcavity structure with dual cavity modes is
useful for the generation of entangled photon pairs, for achieving the
strong-coupling regime between exciton and photon, and for high resolution
multi-wavelength filters in optical communication.
