A systematic study of how the erbium-doped fiber amplifier (EDFA) gain behaves inside an active recirculating delay line structure is presented. It is verified using a representation of an active-fiber Bragg-grating-pair filter. It shows that due to the presence of the recirculating signal, the EDFA gain inside the cavity exhibits hard saturation, and with a proper design, fluctuations in pump power have only slight effects on EDFA gain and this enables the active delay line filter to realize a stable high-Q frequency re- sponse. Results demonstrate a high-Q photonic signal processing filter that exhibits low sensitivity to pump power perturbations and which shows robust active filter operation.
Chan, E. H. W., & Minasian, R. A. (2004). Erbium-doped fiber amplifier gain characteristics inside active delay line structures. IEEE Photonics Technology Letters, 16(10), 2338-2340. https://doi.org/10.1109/LPT.2004.834484