The effects of co-doping GeO 2 and Al³⁺on ytterbium-doped silica-based fiber

Abstract

Four types of YDFs with different Al 3+ concentration and mole content of GeO 2 were manufactured and the refractive index and absorption spectra of these fibers were explored. With the comparison of four YDFs and detailed analyze, it was found that higher Al 3+ concentration leads to more GeO 2 volatilization, which results in the refractive index decrease. Therefore, mole content of GeO 2 should be increased when co-doping Al 3+ in YDF to maintain numerical aperture. Meanwhile, the temperature of making porous layer should be controlled exactly to obtain good repetition of Al 3+ -codoped YDF as the little change of temperature has little effect on mole content of GeO 2 and S i O 2 but has great effect on compactness of porous layer. By drawing the fiber and testing the related parameters, the results show that the optimum temperature range for making soot layer should between 1440℃ and 1480℃ where the absorption coefficients were as high as 620dB/m with better repeatability. Finally, the ratio of GeO 2 to S i O 2 should be controlled to obtain long fluorescence lifetime for fabricating highly ytterbium-doped fiber with required numerical aperture.