Modeling of Active Fiber Loop Ring-Down Spectroscopy Considering Gain Saturation Behavior of EDFA

Active fiber loop ring-down spectroscopy (FLRDS) can achieve a high-finesse fiber cavity by introducing the erbium-doped fiber amplifier (EDFA) gain for highly sensitive detection. However, gain saturation behavior of the EDFA induces pulse-to-pulse gain fluctuations, which cause the ring-down signal to deviate from the exponential-decay law and greatly destroy the detection accuracy of active FLRDS. In order to analyze active FLRDS more accurately, a theoretical model of active FLRDS considering the gain saturation behavior of the EDFA is established. The performance of the active FLRDS system is simulated and discussed by using the model. The dependence of the system performance on the initial optical power, the inherent cavity loss, the test-gas concentration and the EDFA location is deeply researched. The model is applicable to the active FLRDS systems used for many sensing applications, such as trace gas, temperature, refractive index, strain, and pressure.