Stimulated Brillouin scattering of helical Bloch modes in 3-fold rotationally symmetric chiral 4-core photonic crystal fibre

Stimulated Brillouin scattering (SBS) in optical fibres, in which guided light is parametrically reflected by coherent acoustic phonons, provides a powerful and flexible mechanism for controlling light, and has recently been demonstrated with orbital angular momentum (OAM) modes in a special annular-core fibre [1] . Helically twisted photonic crystal fibre (PCF) robustly supports circularly-polarised helical Bloch modes (HBMs) and displays OAM birefringence, i.e., modes with equal and opposite OAM orders have different propagation constants [2] . Here we report for the first time SBS of circularly-polarised HBMs in a chiral 4-core PCF with 3-fold symmetry.