Coherent combining of 7 fiber lasers using a multi-plane light converter device

An experimental demonstration of laser beam coherent combining with active phase control has been performed using for the first time a Multi-Plane Light Converter device (MPLC). The MPLC as a beam combiner is designed as a spatial multiplexer which output modes form a Gaussian beam when superimposed constructively, reaching theoretically 100% efficiency. Moreover, reflective free-space design allows for handling high power. The experiment combines seven 1.5 itm continuous wave fiber lasers operated at a low power level in the tens of milliwatt range using the frequency-tagging LOCSET technique (Locking of Optical Coherence by Single-detector Electronic-frequency Tagging) for the phase locking. 72-% power efficiency MPLC CBC is achieved with an output combined beam close to a Gaussian beam profile. M-2 is lower than 1.8 depending on the transverse direction, revealing an excellent quality for the combined beam. The output beam is more than 94 % linearly polarized. Simulation of the impact of atmospheric turbulence on the propagation of the seven laser beams up to 1 km is performed. We demonstrate that it is possible to compensate for most of the atmospheric propagation detrimental effects and to perform efficient MPLC CBC through strong turbulence.