For many applications, all fiber linearly polarized laser is required. However,Stimulated Brillouin Scattering (SBS) gain is higher for linearly polarized laser propagating in polarization maintaining (PM) fiber .Therefore, power scaling of linearly polarized narrow linewidth fiber amplifier is even more difficult.

Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) demonstrated a 170 W all-fiber linearly-polarized single-frequency sing-mode ytterbium amplifier at 1064 nm with an optical efficiency of 80%. They used a 3.9 m long ytterbium-doped polarization maintaining fiber with a core diameter of 10 μm as the gain fiber, which guarantees a diffraction-limited output with a measured M² of 1.02. To suppress the stimulated Brillouin scattering, they used longitudinally varied strains on the gain fiber according to the signal power evolution and the temperature distribution. They achieved 7 times increase of the stimulated Brillouin scattering threshold .[Optics Express, Vol. 21, Issue 5, pp. 5456-5462 (2013)].