Raman amplification
Encyclopedia
Raman amplification is based on the Stimulated Raman Scattering
(SRS) phenomenon, when a lower frequency 'signal' photon
induces the inelastic scattering
of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result of this, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium. This process, as with other stimulated emission
processes, allows all-optical amplification. Optical fiber
is today mostly used as the nonlinear medium for SRS, for telecom
purposes; in this case it is characterized by a resonance frequency downshift of ~11 THz (corresponding to a wavelength shift at ~1550 nm of ~90 nm). The SRS amplification process can be readily cascaded, thus accessing essentially any wavelength in the fiber low-loss guiding windows (both 1300 and 1550). In addition to applications in nonlinear and ultrafast optics, Raman amplification is used in optical telecommunications, allowing all-band wavelength coverage and in-line distributed signal amplification.
Raman scattering
Raman scattering or the Raman effect is the inelastic scattering of a photon. It was discovered by Sir Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan in liquids, and by Grigory Landsberg and Leonid Mandelstam in crystals....
(SRS) phenomenon, when a lower frequency 'signal' photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
induces the inelastic scattering
Inelastic scattering
In particle physics and chemistry, inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved . In an inelastic scattering process, some of the energy of the incident particle is lost or gained...
of a higher-frequency 'pump' photon in an optical medium in the nonlinear regime. As a result of this, another 'signal' photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium. This process, as with other stimulated emission
Stimulated emission
In optics, stimulated emission is the process by which an atomic electron interacting with an electromagnetic wave of a certain frequency may drop to a lower energy level, transferring its energy to that field. A photon created in this manner has the same phase, frequency, polarization, and...
processes, allows all-optical amplification. Optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
is today mostly used as the nonlinear medium for SRS, for telecom
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
purposes; in this case it is characterized by a resonance frequency downshift of ~11 THz (corresponding to a wavelength shift at ~1550 nm of ~90 nm). The SRS amplification process can be readily cascaded, thus accessing essentially any wavelength in the fiber low-loss guiding windows (both 1300 and 1550). In addition to applications in nonlinear and ultrafast optics, Raman amplification is used in optical telecommunications, allowing all-band wavelength coverage and in-line distributed signal amplification.