Very large mode area Solid-Core Photonic BandGap fiber laser with hetero-structured cladding and Yb-doped Sol-Gel core

Single-Mode Large Mode Area (SM-LMA) fibers are highly demanded for high power laser applications, due to the quality of the beam they deliver together with reduced impairments caused by non-linear effects. Even though LMA fibers demonstrated large progress during the last decade, the need for flexible, active or passive LMA fibers still persists. Besides this, fiber-integrated functionalities, like spectral filtering or chromatic dispersion control can be needed. In this context, Solid-Core Photonic BandGap (SC-PBG) fibers appear as good candidates for the realization of LMA structures. Recently, based on the concept introduced by Murao et al. in 2009 [1], we experimentally demonstrated that High Order Modes (HOM) can be removed by hetero-structuring the cladding in SC-PBG fibers. Thus, by introducing 6 outer cores around the central one, it has been possible to fabricate passive LMA fiber with a mode field diameter (MFD) of 44 μm when working in the 4^th PBG and a MFD of 33 μm when working in the 3^rd PBG [2]. In the present work, this concept is extended to double-clad active fiber.