Self-imaging-based high-power all-fiber coherent combiners: fabrication and preliminary demonstration

Self-imaging combiners can achieve near-perfect filled-aperture coherent beam combination in an all-fiber format with a high-power operation capability. In this Letter, the fabrication of proposed self-imaging combiners is presented, along with a demonstration of a 2 × 2 configuration that uses commercially available large-mode-area fibers, glass tube and square-core fiber. Two types of self-imaging combiners have been fabricated using polarization-maintaining fibers and non-polarization-maintaining fibers, respectively, and these have been tested in an all-fiber coherent beam combination system. Preliminary results reveal that non-polarization-maintaining fibers can achieve better positioning precision, and a maximal combining efficiency of 52.7% has been achieved. The deviation of the demonstrated combining efficiency from the theoretical prediction is mainly attributed to the distortion of the fiber bundle and square-core output fiber, which can be further improved by refining the fabrication process and employing specially developed square-core fiber with better geometrical precision. To the best of the authors' knowledge, this is the first validation of all-fiber coherent beam combining based on the self-imaging effect.