Low-spatial coherence vortex beam generation by random distributed feedback fibre laser

Abstract

Vortex beams with low spatial coherence have great potential in applications such as imaging, medical diagnosis, optical communication, and manipulation. In this study, we experimentally demonstrated a radially polarised vortex beam with extremely low spatial coherence using a random distributed feedback fibre laser (RDFB-FL). The results show that the spatial coherence of vortex beams can be reduced in an RDFB-FL and further reduced by introducing radial polarisation. In addition, the evolution of the spatial coherence of a RDFB-FL-generated vortex beam with varying pump power was clearly revealed for the first time. The spatial coherence first decreases sharply up to a point as the pump power increases and then remains constant, and this behaviour is quite different from that of vortex beams generated by conventional fibre lasers. The present study provides an effective method for achieving a low-spatial coherence vortex beam source for application in telecommunications and imaging systems.