Raman amplification 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, in which a lower frequency 'signal' induces of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the.