Automatic intensity control of an optical transmission line using enhanced gain saturation in cascaded optical amplifiers

The output characteristics through an optical transmission system with multiple optical amplifiers which operates in the gain-saturation regime have been studied in both a uniformly pumped laser amplifier and an erbium-doped fiber amplifier with pump absorption. It has been shown that the output intensity becomes almost constant in the optical system if the input intensity changes within the gain-saturation regime of the amplifiers. The stabilization of the output intensity is greatly enhanced by cascading the saturated optical amplifiers. There is a characteristic input intensity which causes no intensity changes at the output end of the transmission line. This technique is applicable to soliton transmission as well as to ordinary pulse communications