In-line Raman amplifiers provide distributed gain along the optical fiber, significantly improving the optical signal-to-noise ratio (OSNR) compared to traditional lumped amplifiers like EDFAs, which enables longer transmission spans in long-haul terrestrial and submarine networks. In-line Raman amplifiers provide distributed gain along the optical fiber, significantly improving the optical signal-to-noise ratio (OSNR) compared to traditional lumped amplifiers like EDFAs, which enables longer transmission spans in long-haul terrestrial and submarine networks. Raman amplification / ˈrɑːmən / is a way of increasing the signal strength in an optical fiber. It is often used in a fiber that carries a signal for a long distance (such as in an undersea cable). Technically, it works by stimulating Raman scattering, in which a lower frequency 'signal' photon. One of the main advantages of Raman amplifiers is that they can be used to amplify a wide range of wavelengths, from the near-infrared to the visible spectrum. This makes them versatile and adaptable to a variety of applications. Unlike EDFAs, which are limited to the C-band and L-band, Raman amplifiers can operate in any spectral region where pump lasers. The higher energy levels are not stable states so they quickly decay to lower intermediate energy levels releasing energy as photons in any direction at lower frequencies.