Coherent combining of multi-wavelength fiber amplifiers using a stochastic parallel gradient descent algorithm

Multi-wavelength and non-single-frequency seed lasers can be used to suppress stimulated Brillouin scattering and improve the ultimate output power of a fiber laser amplifier. Coherent combining of non-single-frequency and/or multi-wavelength lasers/amplifiers is a promising way to obtain much higher total output power than from coherent combining of single-frequency lasers/amplifiers. Using a stochastic parallel gradient descent algorithm, we demonstrate coherent combining of four-channel multi-wavelength lasers in a master oscillator power amplifier (MOPA) configuration. Four lasers with different wavelengths, namely two non-single-frequency and two single-frequency lasers, are used. The mean power of the main lobe in the closed-loop case is three times that for the open-loop case, approaching 75% of its ideal value. The coherent combining of multi-wavelength and non-single-frequency lasers in a MOPA configuration is validated, and a feasible approach for scaling to high power coherent combining is provided.