  We describe a fiber ring resonator comprised of a relatively long loop of
standard single-mode fiber with a short nanofiber segment. The evanescent mode
of the nanofiber segment allows the cavity-enhanced field to interact with
atoms in close proximity to the nanofiber surface. We report on an experiment
using a warm atomic vapor and low-finesse cavity, and briefly discuss the
potential for reaching the strong coupling regime of cavity QED by using
trapped atoms and a high-finesse cavity of this kind.
