Theoretical investigation of an optical fiber amplifier loop for intra-cavity and ring-down cavity gas sensing

An optical fiber amplifier loop (OFAL) for intra-cavity and ring-down cavity gas sensing is proposed in this paper. The action of the OFAL is investigated theoretically. A uniform model of the system is established using rate equations, from which the sensitivity enhancement factor can be obtained. Based on the model, the effects of pump power and system loss on the performance of the OFAL are deeply researched. At the same time, the expressions of the sensitivity for intra-cavity and ring-down cavity are deduced and discussed respectively. And the simulation of the sensitivities depending on the pump power and system loss is realized, which leads to the theoretical values of the system sensitivity limit.