The self-imaging effect in a square core fiber has been investigated, and an integrated all-fiber combiner has been proposed based on a large mode area double clad fiber, which can be employed to construct high power coherent beam combining sources in the all-fiber format. The influence of various parameters on beam quality (
M
2
) and efficiency of the all-fiber coherent beam combiner has been studied numerically, which reveals that the near diffraction-limited laser beam can be achieved. A principle demonstration of the self-imaging effect has been carried out experimentally in a square core fiber, which proves the feasibility of beam combining with the square fiber, and that it is a promising way to develop high power coherent beam combination sources.
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.
An all-fiber structure 2×2 coherent beam combiner based on
large-mode-area fiber and square-core fiber has been fabricated. Four
lasers coherently combined using such combiner showed 52.7% of
efficiency in the central lobe.
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