Effect of Optical Delay on the Suppression of the Power Transient Excursion in a Combined Gain‐Controlled Erbium‐Doped Fiber Amplifier

This report describes the effect of optical delay on the suppression of the power transient excursion in a combined gain‐controlled erbium‐doped fiber amplifier with an internal optical feedback loop (OFL). A simple homogeneous model showed that the optical delay caused a phase change in the oscillation of the surviving and laser channels, which resulted in a reduction of the overall power transient excursion. In addition to the reduction, a real system with a 1528.7‐nm OFL shifted the oscillation upward or downward according to channel removal or addition, whereas another one with a 1560.9‐nm OFL did not. This different transient behavior reflected a control‐wavelength dependence on optical automatic gain control, where spectral‐hole burning dominated over relaxation oscillation for 1528.7 nm, and vice versa for 1560.9 nm.