An optical waveguide includes a waveguide body and a film disposed on a surface of the waveguide body. The film includes a base and a plurality of undercut light extraction elements disposed between the base and the surface.
REFERENCE REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under contract DE-EE0006264 awarded by the U.S. Department of Energy. The government has certain rights in the invention.