High-Coherence Brillouin Fiber Laser Based on a Stabilized Optical Cavity

We experimentally demonstrate a stabilized single-frequency Brillouin fiber laser operating at 1.06-µm wavelength by means of a passive highly nonlinear fiber ring cavity combined with a phase-locking loop scheme. The stimulated Brillouin scattering efficiency is first investigated in distinct single-mode germanosilicate (GeO₂) core optical fibers with increasing GeO₂ content. The most suitable fiber, namely, 21 mol.% core content fiber, is used as the Brillouin gain medium in the laser cavity made with a 15-m-long segment only. A Stokes lasing threshold of 140 mW is reported. We also show significant spectral linewidth narrowing (well below 1 kHz) as well as frequency and phase noise reduction compared to that of the initial pump in our mode-hop free Brillouin fiber laser.