  Micron-scale optical cavities are produced using a combination of template
sphere self-assembly and electrochemical growth. Transmission measurements of
the tunable microcavities show sharp resonant modes with a Q-factor>300, and
25-fold local enhancement of light intensity. The presence of transverse
optical modes confirms the lateral confinement of photons. Calculations show
sub-micron mode volumes are feasible. The small mode volume of these
microcavities promises to lead to a wide range of applications in microlasers,
atom optics, quantum information, biophotonics and single molecule detection.
