A forward Brillouin fibre laser

Highly-coherent and narrow linewidth fibre lasers are determinant in several sensing techniques. Here the authors develop a laser based on forward Brillouin scattering achieving ultra high coherence in single-, few- and multi-mode operation regimes. Fibre lasers based on backward stimulated Brillouin scattering provide narrow linewidths and serve in signal processing and sensing applications. Stimulated Brillouin scattering in fibres takes place in the forward direction as well, with amplification bandwidths that are narrower by two orders of magnitude. However, forward Brillouin lasers have yet to be realized in any fibre platform. In this work, we report a first forward Brillouin fibre laser, using a bare off-the-shelf, panda-type polarisation maintaining fibre. Pump light in one principal axis provides Brillouin amplification for a co-propagating lasing signal of the orthogonal polarisation. Feedback is provided by Bragg gratings at both ends of the fibre cavity. Single-mode, few-modes and multi-mode regimes of operation are observed. The lasing threshold exhibits a unique environmental sensitivity: it is elevated when the fibre is partially immersed in water due to the broadening of forward Brillouin scattering spectra. The results establish a new type of fibre laser, with potential for ultra-high coherence and precision sensing of media outside the cladding.

Automated summary

This study reports a fibre laser based on forward Brillouin scattering, which has high coherence and narrow linewidth. The laser demonstrates good performance in single-, few-, and multi-mode operation regimes, and shows sensitivity to the environment, making it suitable for precision sensing.