Home-made confined-doped fiber with 3-kW all-fiber laser oscillating output

Abstract

Ytterbium doped fiber lasers (YDFLs) with small volume, good beam quality, good heat dissipation performance and high conversion efficiency are widely used in industrial processing, military, medical and other fields. In past decades, with the development of high-performance double cladding gain fiber and fiber devices, the output power of YDFLs increases rapidly. However, nonlinear effects (NLEs), such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), are produced, which limits the further enhancement of the output power of fiber laser. Large mode area ytterbium-doped fiber (LMAYDF) can effectively increase the nonlinear effect threshold. However, increasing the core diameter will support more high-order modes (HOMs), which may lead the beam quality to deteriorate and induce the mode instability (MI) effect to occur in fiber lasers. Thus, MI and NLEs have become the main limiting factors for the further improving of output power and beam quality in fiber lasers. The confined-doped ytterbium-doped double-clad fiber (CDYDF), by reducing the doping diameter of gain ions in the fiber core, makes the fundamental mode (FM) dominate in mode competition and HOM suppressed to achieve LMAYDF gain control for different modes, thus improving the output power of the fiber laser and maintaining good beam quality. The 33/400 μm confined-doped ytterbium-doped double-clad fiber (CDYDF) is fabricated by modifying the chemical vapor deposition (MCVD) process with solution doping technology (SDT). The Yb<sup>3+</sup> doping diameter ratio is 70% and refractive index profile is close to step-index. Utilizing the master oscillator power amplifier (MOPA) system the beam quality optimization effect of confined-doped fiber is verified and optimized to 1.43 as the power increases while the <i>M</i><sup>2</sup> of seed laser is 1.53. An all-fiber structure counter-pumped fiber oscillator is constructed to test the laser performance of home-made confined-doped fiber. When the pump power is ~4.99 kW, laser power of 3.14 kW with a central wavelength of 1081 nm and line width of 3.2 nm at 3 dB is obtained. Moreover, there is no MI nor SRS in the whole experiment. We demonstrate that it is the highest output power based on home-made confined-doped fiber. The above results indicate that confined-doped fibers have the potential to achieve high-power and high-beam-quality fiber laser output.