An optical beam waveguide consisting of a central aperture and a surrounding lens—a hybrid lens guide—possesses some important advantages of both iris guides and lens guides. Compared to an iris guide, it has a lower loss, and for small curvatures, is less sensitive to bends. Also it is less subject to breakdown than a lens guide. A theoretical study is presented. The hybrid lens guide can be specified by four parameters; the loss is investigated as such effects are also discussed.
J. W. Y. Lit and D. L. Van Rooy, "Hybrid Lens Beam Waveguide," Appl. Opt. 12, 749-754 (1973)