An optical waveguide can include a first region (12), a core (14) and a cladding (16). The core (14) surrounds the first region (12), and the cladding (16) surrounds the core (14). Typically, the core (14) includes an active material. In a further aspect, the invention features a system that includes...http://www.google.fr/patents/US7437041?utm_source=gb-gplus-shareBrevet US7437041 - Ring core fiber
