Collimated directional emission is essentially required an asymmetric
resonant cavity. In this paper, we theoretically investigate a type of
peanut-shaped microcavity which can support highly directional emission with
the emission divergence as small as 2.5o. The mechanism of the collimated
emission is explained with the short-term ray trajectory and the intuitive lens
model in detail. Wave simulation also confirms these results. This extremely
narrow divergence of the emission holds a great potential in highly collimated
lasing from on-chip microcavities
