Power Thresholds and Pump Depletion in Brillouin Fiber Amplifiers

ABSTRACT

The Brillouin fiber amplifier (BFA) has been used in Brillouin optical time (frequency) domain analyzer based sensors. The performance of this sensor depends on pump depletion which occurs when the threshold is reached and when the Brillouin gain is saturated. Although threshold definitions are common for Brillouin fiber generators (BFG), there is no explicit threshold definition for BFA. More importantly we find the maximum gain point corresponds to the optimized distributed sensing system where the depletion effect remains small to moderate. We find that only the method based on the determination of the power for which the pump becomes depleted, and hence, the Stokes gain saturated (i.e. inflexion method), remains valid for BFA. We also derive an analytical relation accounting for the various sensor key parameters such as fiber type and length as well as input Stokes power. The thresholds obtained with the analytical relation are within 10% of experimental and numerical values, which is maximum power that can be launched for a given optimum sensing configuration.