kHz Closed Loop Interferometric Technique for Coherent Fiber Beam Combining

An architecture for large bandwidth active coherent fiber beam combining using interferometric measurement is demonstrated. The phases of all the fibers are extracted from a single image recorded on a high speed camera. To the best of our knowledge, this is the first time that the kHz regime is achieved with this technique. Our system, composed of 16 independent fiber channels, is used to evaluate the phase locking stability achieved with this technique. We also show that a minimum of 8 pixels per fiber on the camera is required for a stable close loop operation with a residual phase error of λ/20 rms, which demonstrates the scalability of this concept.