Abstract
Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb3+-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb3+/Al3+/F-/P5+-co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al3+/F-/P5+ in Yb3+-doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb3+. The spectroscopic properties of Yb3+ ions have not deteriorated by the co-doping of F- and P5+ in YAFP glass compared with that of Yb3+/Al3+ co-doped silica glass. A large-size (⌀5 mm × 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 × 10-4 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10-4, was prepared. A LMA PCF with 50 µm core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M2 of 1.4.
Highlights
Yb3+-doped silica fibers have been the most important gain medium for high-power laser applications, owing to the small quantum defect of Yb3+ ions and the excellent mechanical strength of silica glass [1,2,3]
Our groups have been committed to the preparation of large Yb3+-doped silica glass rod with low refractive index and high optical homogeneity by modified sol-gel method combined with high-temperature sintering
For an effective single-mode operation of Large mode area (LMA) photonic crystal fiber (PCF), the refractive index of core glass should be nearly equal to the cladding pure silica glass to ensure low numerical aperture (NA)
Summary
Yb3+-doped silica fibers have been the most important gain medium for high-power laser applications, owing to the small quantum defect of Yb3+ ions and the excellent mechanical strength of silica glass [1,2,3]. Our groups have been committed to the preparation of large Yb3+-doped silica glass rod with low refractive index and high optical homogeneity by modified sol-gel method combined with high-temperature sintering. To the best of our knowledge, our work presents the first-time report of a large-size (⌀5 mm × 90 mm) Yb3+/Al3+/F–/P5+-co-doped silica glass rod with high optical homogeneity and a low refractive index, fabricated by solgel method combined with high-temperature sintering. Using this core-glass rod, a LMA PCF with a core diameter of 50 μm was prepared
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