Abstract: An optical amplifier for amplifying an optical signal along a transmission path. The optical amplifier includes a tunable pump source that provides optical energy to a gain medium arranged along the transmission path and the tunable pump source can be tuned in at least frequency to provide controlled or optimized amplification of the optical signal. In particular, the frequency of the tunable pump source may be controlled based on a detected characteristic of the optical signal and/or may also be controlled to periodically vary, either continuously or discretely, over a pump frequency range that is related to an optical signal frequency range of the optical signal. In a particular case, the pump frequency range may be related to the optical signal frequency range in such a way that the tunable pump source provides Raman amplification over the optical signal frequency range.