Gap solitons on a ring
  We introduce a new species of gap solitons (GSs) supported by an azimuthally modulated guiding ring in defocusing cubic media. The periodicity in the azimuthal direction strongly modifies properties and existence domains of GSs. In addition to the fundamental solitons, we report even and twisted bound states. The former type is found to be stable, while the twisted states are always unstable in defocusing media. 
Yaroslav V. Kartashov, Boris A. Malomed, Victor A. Vysloukh, Lluis   Torner