Manipulating refractive index, homogeneity and spectroscopy of Yb^3+-doped silica-core glass towards high-power large mode area photonic crystal fiber lasers

Abstract

Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb/Al/F/P-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 Al/F/P in Yb-doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb. The spectroscopic properties of Yb ions have not deteriorated by the co-doping of F and P in YAFP glass compared with that of Yb/Al 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 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10, 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 M of 1.4.

Structural origin of thermally induced refractive index changes in Yb3+/Al3+/P5+/F−‐co‐doped silica glass

“…This method has been depicted in our earlier work. 15 This core glass is denoted as YbAPF0.85, in which 0.85 corresponds to the P/Al molar ratio. The oxide content of the YbAPF0.85 glass was measured via an inductively coupled plasma atomic emission spectrometer (ICP-AES, Thermo iCAP 6300), as depicted in Table 1.…”

“…The 0.12Yb 2 O 3 ‐3.2Al 2 O 3 ‐2.7P 2 O 5 ‐93.98SiO 2 (in mol%) core glass with a F/Si mass ratio of 1% was prepared via an improved sol‐gel method. This method has been depicted in our earlier work 15 . This core glass is denoted as YbAPF0.85, in which 0.85 corresponds to the P/Al molar ratio.…”

Optical Fibre-Based Sensors for Oil and Gas Applications

“…A core with a higher refractive index facilitates higher light confinement [148] which in turn increases the propagation distance of the light signal. One approach to manipulate the core refractive index is through rare-earth doping [149][150][151]. The refractive index of glass increases with increasing rare earth concentration [152].…”

Ion-Doped Photonic Crystal Fiber Lasers

“…In recent years, several researchers have used chemical vapor deposition techniques to prepare photonic crystal fibers with very low numerical apertures using various co-doping ions such as Yb 3+ /Al 3+ /P 5+ and Yb 3+ /Al 3+ /F − . For example, in their study of large-mode field photonic crystal fiber lasers, Wang et al (2017) successfully prepared a fiber with a core diameter of 50 μm using Yb 3+ /Al 3+ /P 5+ /F − co-doping and achieved a laser output with an average power of 97 W, a peak power of 93 kW, and a beam quality of 1.4. Since high-power fiber lasers in the 1.5 µm band have a wide range of applications and the gain medium for fiber lasers in this band is usually a double-clad erbium-ytterbium co-doped fiber, so that ytterbium-erbium co-doped photonic crystal fibers dominate among other dopant ions, Of which Wang et al (2014) studied large-mode field fiber lasers using erbium-ytterbium co-doping in a stable laser output with a maximum power of 1.6 W and a center wavelength of 1,534.5 nm obtained in a 600 mm length photonic crystal fiber.…”