We study a new nonlinear beam cleaning fiber laser architecture to obtain high energy polarized pulses with a good beam quality and a narrow linewidth, which is very attractive for fiber-based coherent lidar applications. The set-up involves stimulated Brillouin scattering in an injection seeded arrangement to proceed the cleanup of an aberrated wavefront coming from a large core Er:Yb co-doped fiber amplifier, operating at 1.55 μm. Both theoretical and experimental results are presented, and we report the conversion of a multimode depolarized beam into a near diffraction limited polarized beam with an efficiency of 50%, while preserving the master oscillator linewidth.