Coherent Beam Combining (CBC)

The coherent combining of laser systems allows the scaling of average laser power to multiple 10 kWs, while ideally maintaining beam quality of the individual laser channels. This opens up new fields of laser applications in dynamic material processing, aerospace, defense or space missions.

The most promising approach for power scaling relies on a beam combiner unit having an extremely precisely arranged hexagonal fiber array based on a tiled aperture approach (i.e., side-by-side combining). More than 200 channels can be coherently combined within a compact beam combiner head not larger than a commonly used QBH connector. Each fiber channel in the hexagonal array can be operated with an ytterbium (1µm), erbium (1.5µm) or thulium (2µm) narrow linewidth amplifier. The beam delivery fibers that connect the fiber amplifier with the beam combiner need to be carefully chosen to mitigate stimulated Brillouin scattering (SBS) and maintain beam quality. Ultrafast phase modulators enable control and compensation of the relative phase between the channels, allowing for a coherent superposition of all channels in the far field.

FiberBridge Photonics is a world-leading manufacturer of ultra-precise, monolithic fiber arrays with more than 120 channels that are tested up to 3 kW per channel. This enables laser systems beyond the 100 kW regime.

These kinds of CBC systems typically achieve up to 75% combining efficiency with excellent beam quality. Phase control also allows for ultrafast beam steering or wavefront corrections – an essential tool for the correction of atmospheric turbulences in real-world applications. Additionally, beam shaping of the output beam (coherent and incoherent) is also possible, and enables an even wider range of applications, including dynamic material processing (e.g., 3D printing or welding).