Efficient optical path folding by using multiple total internal   reflections in a microcavity
  We propose using an asymmetric resonant microcavity for the efficient generation of an optical path that is much longer than the diameter of the cavity. The path is formed along a star polygonal periodic orbit within the cavity, which is stable and confined by total internal reflection. We fabricated a semiconductor device based on this idea with an average diameter of 0.3 mm, and achieved a path length of 2.79 mm experimentally. 
Susumu Shinohara, Satoshi Sunada, Takehiro Fukushima, Takahisa   Harayama, Kenichi Arai, Kazuyuki Yoshimura
physics.optics