Depolarized fiber lasers and respective methods are provided for increasing the SBS (stimulated Brillouin scattering) threshold. The laser source is constructed by a frequency-broadened seed source having a frequency bandwidth of less than 50GHz, and the depolarization of the seed source is carried out at time scales shorter than 10ns. At least one amplifier is configured to receive and amplify radiation from the frequency-broadened seed source and deliver the amplified radiation in the optical fiber. Depolarization may be achieved in various ways (e.g., using an interferometer with added length to one arm) and is kept at time scales shorter than tens of nanoseconds, typically shorter than 5-10ns, which distinguish it from random polarization having polarization changes at longer time scales. Polarization maintaining fibers may be used to further increase the SBS by separating the polarizations states.