A time-division-multiplexing cascaded active phase-locking method for an all-fiber coherent beam combining system

Coherent beam combining (CBC) is an effective approach to exceed the power limitation of fiber lasers by combining multiple laser sources. Phase-locking is one of the important steps in an active CBC system. Many phase-locking methods have already been developed and have effectively achieved phase control. Generally, the phase control bandwidth decreases accordingly as the number of combined lasers increases. This will hamper the development of CBC systems to larger scales. At the same time, the structure of traditional tiled-aperture CBC systems is also a potential limiting factor in the aspect of feedback configuration. An all-fiber CBC structure based on active phase control can avoid physical size limitations on traditional structures and greatly expand the scale of tiled-aperture CBC arrays to over tens of thousands of sub-beams. In such a large array scale, existing phase control methods will inevitably encounter the problem of bandwidth reduction. To solve this problem, we propose a time-division multiplexing cascaded (TDMC) active phase-locking method in this paper. Simulation studies on phase control of over 10,000 laser beams are conducted. The method shows huge bandwidth enhancement in control phases of a large number of lasers. This will lay the technological foundation for further expanding the number of an all-fiber tiled-aperture array.