Diameter-dependent optical losses in pillar microcavities

Optical losses in pillar microcavities have been measured directly by means of microreflectance spectroscopy. It was shown that optical losses of the cavities larger than about 3 μm were constant irrespective of the diameters. The lasing thresholds were also measured, and they were proportional to the cavity volume. This result is consistent with the measured constant optical losses. A drastic increase in optical losses has been observed when reducing the cavity diameters below 2 μm. The scattering losses due to sidewall roughness were considered mainly responsible for the optical losses.