Mamyshev oscillators (MOs) exhibit the potential for generating high average power and ultrashort pulses. Herein, we construct an MO using flexible double-cladding ytterbium-fiber with a fusion-spliced-combiner pumped scheme. Consistent with the most reported research results, the offset filter separation significantly affects the pulse characteristics (spectrum, pulse duration, etc.). Notably, in comparison with red-shifting, blue-shifting the peak spectral emission of the grating filter relative to a constant central wavelength of the bandpass filter substantially enhances the laser output characteristics. This phenomenon, which has not been previously reported, results in an average power up to 2.23 W and a pulse duration as short as 49 fs. To our knowledge, this is the highest average power achieved in sub-50 fs pulse duration in the nonlinear polarization rotation-assisted mode-locked MO laser architecture. The presented technique offers unique scientific proof for developing ultrafast laser sources with higher average power and shorter pulse duration.
