Abstract: A method of preventing contamination of the air channels in the capillaries or pores of an air-clad or photonic-crystal fiber during polishing of the end-faces. A glass or silica fiber rod of diameter comparable to the fiber is fused to the end-face of the fiber, cut, and polished to form a thin protective plate having no appreciable affect on the optical properties of the fiber. Alternatively the air capillaries may be sealed by a UV-curable fluid or by melting the surrounding material. The end-face of the fiber thus presents a polished or cleaved surface for optical coupling to other fibers without causing damage or contamination to the air channels of the fiber. Furthermore, treating both end-faces of an air-clad or photonic-crystal fiber in manner provides a hermetic seal for the air-channels and protects the fiber against degradation caused by contamination such as humidity and dust which would otherwise enter the air channels over the course of time.

Abstract: A fiber optic structure for efficient pumping of a rare-earth element fiber laser, such as an Ytterbium fiber laser, operating at the three-level transition. In order to operate at the three-level transition, a large amount of pumping energy must be effectively coupled from the fiber's inner cladding into the rare-earth element-doped core. The present invention discloses the use of eccentric asymmetric, and non-cylindrical inner claddings to maximize the overlap of the pumping energy of multi-mode field distribution patterns with the fiber core and to maximize the number of intersections of the pumping optical ray trajectories with the core. While the cladding surrounding the core is eccentric with respect to the core, the core itself is coaxial with the outer cladding for compatibility in coupling to standard transmission fibers. Also disclosed is the use of air claddings and methods for optimal sizing of the capillaries.