Abstract: The dynamic gain control system includes a pump source providing pump light. The dynamic gain control system measures a certain portion of the input pump light into the optical amplifier and measures a certain portion of the output pump light from the optical amplifier. The dynamic gain control determines the pump light loss based on the input pump light and output pump light measurements. Based on the pump light loss, the dynamic gain control system maintains the pump light loss relatively constant (for example 0.1 dB) independent of the number of input channels and their relative powers (for example, input channel powers of +50 dBm to 10 dBm) by providing feedback to control the output pump light. In doing so, the dynamic gain control system maintains the inversion level of the optical amplifier. A relatively constant inversion level corresponds to only small variations in the gains of the input channels (multi-channel gain) as a result of changes in the input channels to the optical amplifier.

Abstract: The invention relates to an optical amplifier comprising an input and a beamsplitter connected by a first optical fiber arranged to transmit an optical signal from said input to said beamsplitter via an optical amplifying means and an optical isolator. The optical amplifier includes a second optical fiber connected between said input and said beam splitter and is arranged to transmit a second signal from said beamsplitter to said input. Preferably, the optical amplifier also incorporates an optical element which is adapted to prevent any signal from said input propagating along said second optical fiber and to prevent any signal from said second optical fiber from propagating along said first optical fiber.