Low numerical aperture large-mode-area neodymium-doped fibers fabricated by SPCVD and ASD for laser operation near 920nm

摘要

We present the fabrication by Surface Plasma Chemical Vapor Deposition (SPCVD) and All Solution Doping (ASD) of step-index Nd-doped fibers with a 30/125μm (core/cladding diameters) geometry and a low numerical aperture (NA) near 0.05. A phospho-alumino-silicate (SiO_2-Al_2O_3-P_2O_5-Nd_2O_3) core composition was used to reduce the formation of Nd~(3+) ions clusters while keeping a low refractive index through the peculiar AlPO_4 chemical complex. Operated in CW laser regime, a 0.053 NA fiber generated up to 17W of output power at 921nm, limited by the available pump power at 808nm (51W), yielding a 37% power conversion efficiency. The profile of the output beam for a bend diameter of ～12cm is gaussian and nearly diffraction limited (M~2 ～ 1.1). This is in good agreement with the large discrepancy, in terms of calculated bending losses, between the fundamental LP_(01) and the higher order modes.