  We study a Fabry-Perot cavity formed from a ridge waveguide on a AlGaAs
substrate. We experimentally determined the propagation losses in the waveguide
at 780 nm, the wavelength of Rb atoms. We have also made a numerical and
analytical estimate of the losses induced by the presence of the gap which
would allow the interaction of cold atoms with the cavity field. We found that
the intrinsic finesse of the gapped cavity can be on the order of F ~ 30,
which, when one takes into account the losses due to mirror transmission,
corresponds to a cooperativity parameter for our system C ~ 1.
