  We give a theoretical treatment of single atom detection in an compound,
optical micro cavity. The cavity consists of a single mode semiconductor
waveguide with a gap to allow atoms to interact with the optical field in the
cavity. Optical losses, both in the semiconductor and induced by the gap are
considered and we give an estimate of the cavity finesse. We also compute the
cooperativity parameter and show how it depends on the gap width and cavity
length. Maximization of the cooperativity does not always correspond to
maximization of the coupling.
