Abstract

Beam combining of multiple lasers is done to increase the output power levels beyond the achievable power from a single laser. There are two broad methods of beam combining, coherent beam combining (CBC) and spectral beam combining (SBC) [1]. In CBC, the optical phase of all the combining beams needs to be controlled [2]. SBC has advantages over CBC such as not requiring precise phase control of individual beams [3] and graceful degradation of system output power if individual units fail. However, in SBC, each laser needs current and temperature controller and line broadener, making the system uneconomical and complex. This problem can be solved if multiple lasers in SBC are extracted from a single laser. In this work, we demonstrate a frequency comb-based seed source that uses one laser wavelength to generate multiple wavelengths with tunable repetition rate and central wavelength. We use a demultiplexer to extract 200GHz separated carriers in distinct fiber ports. We further experimentally demonstrate that our system enables superior stimulated Brillouin scattering (SBS) suppression through line-shaping the spectrum. In fiber amplifiers, SBS is enhanced due to seeding by back-reflected component of laser spectra. Here we mitigate it by making the spectrum asymmetric by utilizing the suppression band of demultiplexer, which reduces power at Stokes wavelength. With tailored line-shape, the SBS threshold of the system increases by 58%. As a proof of concept, we have demonstrated the proposed architecture in C-band, but the same system can be replicated in other wavelengths (e.g. 1μm) where SBC applications are more important.

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