  Optical non-reciprocity, which breaks the symmetry between forward and
backward propagating optical waves, has become vital in photonic systems and
enables many key devices, such as optical isolators, circulators and optical
routers. Most conventional optical isolators involve magneto-optic materials,
but devices based on optical nonlinearities, optomechanically induced
transparency and stimulated Brillouin scattering (SBS) have also been
demonstrated. So far, however, they have only been implemented for linearly or
randomly polarized LP01-like fundamental modes. Here we report a light-driven
nonreciprocal isolator for optical vortex modes, based on topology-selective
SBS in chiral photonic crystal fibre. The device can be reconfigured as an
amplifier or an isolator by adjusting the frequency of the control signal. The
experimental results show vortex isolation of 22 dB, which is at the
state-of-the-art in fundamental mode isolators using SBS. This unique device
may find applications in optical communications, fibre lasers, quantum
information processing and optical tweezers.
