Non-linear label-free imaging through a multimode graded index optical fibre Angel Cifuentes, Johanna Trägårdh, Tomáš Pikálek, Mojmír Šerý, Denis Akimov, Tobias Meyer, Jürgen Popp, Rodrigo Amezcua-Correa and Tomáš Čižmár EPJ Web Conf., 238 (2020) 04006 Published online: 20 August 2020 DOI: 10.1051/epjconf/202023804006