Simple theoretical approach for spectral properties of Rayleigh backscattering feedback fibre lasers

The reflecting spectral properties of a long low-loss singlemode fibre subject to randomly distributed Rayleigh backscattering feedback are theoretically analysed from the optical beat produced when two-frequency light is input into the fibre. The theoretical results can well explain the recent experimental observations on all-fibre cavity lasers that are featured by the broad continuum of multiple spiky narrowband spectral lines.