Mode-area scaling of helical-core, dual-clad fiber lasers and amplifiers using an improved bend-loss model

摘要

For small-bend radii, the waveguide condition for total internal reflection is violated in a large angular spread of incident angles at the interface of the fiber core. To account for this, we derived an improved semianalytic bend-loss model that allows for the propagation of radiated fields outside the plane of the fiber bend. This new model is applied to large-mode-area helical-core fibers (which require small-bend radii) for use as high-power fiber lasers and amplifiers. In particular, the limits of scaling the mode area while maintaining good beam quality are explored. Single-mode operation is expected for a 40 Am core with a 0.10 numerical aperture, and scaling to a 100 Am core diameter is shown to be possible. Additionally, helical fibers are shown to readily perform where conventional coiled fibers are not appropriate to operate long term. (c) 2006 Optical Society of America.