Frequency stability of a Brillouin fiber ring laser

This study shows theoretical and experimental results on three main effects determining the frequency stability of a Brillouin fiber ring laser, namely: the temperature effects and the nonlinear Kerr and frequency pulling effects. The oscillation frequency in a Brillouin fiber ring laser is determined mainly by the axial mode of the cold resonator located under the Brillouin gain curve that experiences the highest gain. This oscillation frequency is therefore temperature dependent since both the free spectral range (FSR) and the gain curve center depend on the temperature. The FSR variation gives rise to a continuous lasing frequency variation while the gain curve shift leads to mode hopping. In addition to these temperature effects, the nonlinear Kerr effect and the mode pulling effect will also slightly shift the lasing frequency away from the resonant frequency of the cold resonator. The Kerr effect depends only on the pump power, while the mode pulling effect depends on both the pump power and the relative location between the lasing mode and the gain curve center. The results of this study are useful in many BFRL applications such as Brillouin fiber-optic gyroscopes, microwave generators and frequency shifters