A Raman amplifier system includes high-power pump lasers (often diode lasers around 1450–1490 nm for C-band signals), wavelength combiners (couplers or circulators), and fiber spans for gain, see Figure 1. A Raman amplifier is an optical amplifier based on Raman gain, which results from the effect of stimulated Raman scattering in some Raman gain medium. That medium is often an optical fiber (possibly a highly nonlinear fiber), although it can also be a bulk crystal, a waveguide in a photonic. Raman amplification / ˈrɑːmən / is a way of increasing the signal strength in an optical fiber. It discusses key factors influencing Raman gain, noise issues such as amplified.