  The ultralong distance coupling between two Asymmetric Resonant Microcavities
(ARCs) is studied. Different from traditional short distance tunneling coupling
between microcavities, the high efficient free space directional emission and
excitation allow ultralong distance energy transfer between ARCs. In this
paper, a novel unidirectional emission ARC, which shows directionality I40 =
0.54, is designed for materials of refractive index n = 2.0. Compared with
regular whispering gallery microresonators, the coupled unidirectional emission
ARCs show modulations of resonance frequency and linewidth even when the
distance between cavities is much longer than wavelength. The performances and
properties of the ultralong distance interaction between ARCs are analyzed and
studied by coupling mode theory in details. The ultralong distance interaction
between ARCs provides a new way to free-space based optical interconnects
between components in integrated photonic circuits.
