  Amplifying radially and azimuthally polarized beams is a significant
challenge due to the instability of the complex beam shape and polarization in
inhomogeneous environment. In this Letter, we demonstrated experimentally an
efficient approach to directly amplify cylindrical-vector beams with axially
symmetric polarization and doughnut-shaped intensity profile in a picosecond
MOPA system based on a double-clad ytterbium-doped tapered fiber. To prevent
polarization and beam shape distortion during amplification, for the first time
to the best of our knowledge, we proposed using the spun architecture of the
tapered fiber. In contrast to an isotropic fiber architecture, a spun
configuration possessing nearly-circular polarization eigenstates supports
stable wavefront propagation. Applying this technique, we amplified the
cylindrical-vector beam up to 22 W of average power with 10 ps pulses at a
central wavelength of 1030 nm and a repetition rate of 15 MHz, maintaining both
mode and polarization stability.
