Collimated directional emission from a peanut-shaped microresonator
  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. 
Fang-Jie Shu, Chang-Ling Zou, Fang-Wen Sun, and Yun-Feng Xiao
physics.optics