Multimode fibres are often not used for propagating coherent light when the output spatial mode quality is of upmost importance. Since the propagation constant and intensity profile differs for each mode, the coherent superposition of modes results in a highly structured output, even if light was coupled into a single mode at the entrance of the fibre, due to mode coupling. We have demonstrated that by adaptively shaping the wavefront of the incident light at the Fourier plane of the fibre input face, we can significantly improve the free-space mode quality at the Fourier plane of the fibre output by applying a suitable optimisation algorithm and optimisation metric.
