Amplifiers based on Raman gain, which results from the effect of stimulated Raman scattering.

The Raman-active medium is usually an optical fiber, although it can also be a bulk crystal, or a cell with a gas or liquid medium. An input signal can be amplified while co- or counterpropagating with a pump beam, the Wavelength of which is typically a few tens of nanometers shorter. For Silica fibers, maximum Gain is obtained for a Frequency offset of 10–15 THz between pump and signal, depending on the Core composition.