SBS suppression in high brightness, all-fiberized and linearly polarized amplifiers by rectangular spectrum

Stimulated Brillouin scattering (SBS) suppression in high power, narrow linewidth and all polarization-maintained amplifiers with near diffraction limited (NDL) beam quality by rectangular optical spectrum is demonstrated. Rectangular spectrum is generated by using cascaded phase modulations. In the preliminary experiment, output power of 509 W with spectral linewidth of similar to 3 GHz is obtained. At maximal output power, the polarization extinction ratio (PER) is measured to be similar to 14 dB and the beam quality (M-2 factor) is M-2 similar to 1.2. The technique presented give useful reference to control the spectral linewidth in high brightness fiber amplifiers. By combining with other linewidth controlling techniques, several kilowatt-level output power with spectral linewidth of < 10 GHz could be expected.