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 core with a 0.10 numerical aperture, and scaling to a 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.
© 2006 Optical Society of AmericaFull Article | PDF Article
John M. Fini
J. Opt. Soc. Am. B 24(8) 1669-1676 (2007)
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