Non-reciprocal transmission via phase conjugation in multimode optical fibres

We demonstrate phase conjugate correction of modal distortion of a single m ode beam on double-passing a passive highly multimode fibre. Phase conjugat ion is achieved in a self-pumped photorefractive BaTiO3 crystal which conju gates only the e-polarised input component. We show that only a small fract ion of the multimode fibre output is required to faithfully conjugate the s ingle mode input beam. This technique enables the demonstration of a novel nonreciprocal transmission device, which for example has immediate applicat ion in gain-grating holographic resonator designs with multimode fibres as the active gain medium. (C) 2001 Published by Elsevier Science B.V.