Enhanced Supercontinuum Generation in Nonlinear Ytterbium-Doped Fiber Amplifier by Seeding at Short Wavelength

The amplification of a short-pulsed fiber laser along a high-power nonlinear fiber amplifier will undergo nonlinear spectral broadening and temporal distortion with the influence of fiber nonlinear effects. Within the same nonlinear Yb-doped fiber amplifier, we experimentally compared the different spectral and temporal evolution processes of tunable chirped picosecond pulses at different wavelengths (ranging from 1030 to 1070 nm). The comparison results indicate that the generated supercontinuum can be significantly enhanced when the amplifier is seeded at a short wavelength. A comprehensive analysis links the phenomenon to the overlap of Yb³⁺ ion gain and the Raman gain, as well as the additional amplified spontaneous emission seeding effect. The phenomena of nonlinear-effect-induced spectral and temporal center dips were also observed and explained. The proposed conclusion can help to thoroughly understand the nonlinear process in fiber amplifiers and contribute to the development of a high-power spectrally flat amplifier-based supercontinuum source.