Investigation of bending effects on evanescent-field coupled waveguides designed for high-power fundamental-mode deliverysystems

摘要

The objective of the present work is to develop a fiber suitable for high-power fundamental-mode beam delivery over a useful length for material processing (～100 m). The investigated design is based on evanescent-field coupled waveguides, also called multi-core fibers (MCFs). The investigated MCF consists of a hexagonal array of 7 cores in which the fundamental mode, the so-called in-phase supermode, has an effective mode area (A_(eff)) of 348 μrn~2 and a numerical aperture (N.A.) of 0.035. We show how the bending-induced losses and the mode-mixing depend on the bending radius and on the structure of the waveguide. The experimental results on the behavior of the near-field and the far-field for different bending radii will also be reported. Additionally, we will show another method to reproduce experimental results with multi-mode fibers supporting few modes where the conventional approach leads to irreproducible results due to the mode-mixing effect.