Sub-kHz-linewidth broadband-swept fiber laser based on Rayleigh scattering-enabled Brillouin random lasing oscillation with dynamic tunning Brillouin gain spectrum.

A sub-kHz-linewidth broadband-swept fiber laser using Rayleigh scattering-based Brillouin random lasing oscillation is proposed and experimentally demonstrated. Benefiting from Brillouin-involved acoustic damping and arbitrary-wavelength distributed Rayleigh feedback, leveraging instantaneously tuning Brillouin gain spectrum induced by a frequency-sweeping pump, a highly coherent random lasing emission with cavity mode elimination as well as frequency noise suppression is achieved in a sweeping manner. Results show that the proposed sweeping Stokes laser with a two-order-magnitude compressed linewidth of 840 Hz and 20 dB frequency noise suppression can unprecedentedly operate over the maximum wavelength range of 16 nm. Dynamic characteristics of the sweeping laser frequency are experimentally investigated, indicating a minimum residual nonlinearity of 0.0001 within the frequency-sweeping range of 126.63 GHz. It is believed that the proposed swept fiber laser may have attractive potential in diverse applications, including sensing and imaging.