Abstract

Recently, Yb-doped large-mode-area double-cladding Photonic Crystal Fibers (PCFs) with mm-size outer diameter, called rod-type fibers, have been proposed for high-power fiber lasers and amplifiers [1]. Even if the single-mode operation has been experimentally demonstrated for Yb-doped rod-type fiber lasers [1], the guidance of Higher-Order Modes (HOMs) in these PCFs has been shown by numerical analyses [2]. However, a core refractive index fine-tuning offers the possibility to suppress the HOMs [2]. In the present study the effect of a low refractive index ring in the Yb-doped rod-type PCF core on the guided mode propagation has been analyzed through a spatial and spectral amplifier model [2]. The ring provides a higher differential overlap between the Fundamental Mode (FM) and the HOM, stressing the difference between their spatial distributions, with respect to the uniform refractive index core.

© 2009 IEEE