Polarization Influence on Er³⁺-Doped Multi-Wavelength Brillouin Fiber Laser Based on Fiber Loop Mirror

Polarization influences on the performance of multi-wavelength Brillouin Er³⁺-doped fiber laser are investigated by adjusting the polarization controller (PC) in the fiber loop mirror (FLM), where the linear laser cavity is composed of a fiber-tailed mirror and an FLM, and the stimulated Brillouin scattering (SBS) and the Er³⁺-doped fiber amplification (EDFA) simultaneously serve as the cavity gain. We realized 1–7 Brillouin laser lines by increasing the 980 nm pump power. For the first-order Brillouin laser, the signal–noise ratio (SNR) and optical intensity present a sinusoidal envelope; the conversion efficiency changes significantly from 0.56465 dBm/mw to 0.44975 dBm/mw by adjusting the ring’s angle in the PC; the first-order SBS thresholds are 20.4 mw, 36.1 mw and 28.5 mw at different angles θ₂ = 36°, 276° and 300°, respectively; flatness between the two Brillouin lasers change obviously from 2.863 dB to 41.801 dB with different ring angles; the second-order Brillouin laser is suppressed and disappears finally at Δθ₂ = −64° to −84° and 106°~136° angle variation. For the fifth-order Brillouin laser, the highest-order Brillouin laser line is seriously suppressed until it disappears at some angle variations similarly. The powers and wavelength stabilities for one-, three- and seven-wavelength Brillouin fiber lasers were measured in 1 h, and the obtained Er³⁺-doped multi-wavelength Brillouin fiber laser (MWBFL) worked stably during that time, but the stabilities become worse with higher SBS orders.