In scattering based non-linear effects energy gets transferred from an light wave to another wave at a longer wavelength . The lost energy is absorbed by the molecular vibrations, or phonons , in the medium. This second wave if called the stokes wave. The first wave can be thought of as being a pump wave that causes amplification of the stoke's wave. As the pump propagates in the fiber, it loses power and the stokes wave gains power.
In the case of SBS, the pump wave is the signal wave and the Stoke's wave is the unwanted wave that generated due to the scattering process. In the case of SRS. the pump wave is a high-power wave, and the stoke's wave is the signal wave that gets amplified at the pump of the pump wave.
(A)Stimulated Brillouin Scattering (SBS):-
In the case of SBS, the phonons involved in the scattering interaction are acoustic phonons, and the intersection occurs over a very narrow line width. The stoke's and pump waves propagate in opposite directions. Thus SBS does not cause any interaction between different wavelengths, as long as the wavelength spacing is much greater than 20 MHz, which is typically the case SBS can however, create significant distortion with a single channel.
SBS produces gain in the direction opposite to the direction of propagation of the signal, in other words, back toward the source. Thus it depletes the transmitted signal as well as generates a potentially strong signals back toward the transmitter, which must be shielded by an isolator . The SBS coefficient is approximately 4x10 m/w , independent of the wavelength.
(B) Stimulated Raman Scattering (SRS):-
In SRS , if two or more signals at different wavelengths are injected into a fiber, SRS causes power to be transferred from the lower-wavelength channels to the higher - wavelength channels. This coupling of energy from a lower-wavelength signal to a higher-wavelength signal is a fundamental effect that is also the basis of optical amplification and lasers. The energy of a photon at a wavelength is where h is planck's constant
Unlike SBS,SRS is a broadband effect. Its gain coefficient as a function of wavelength spacing. The peak gain coefficient gr is approximately 6x10m/w at 2.55um, which is much smaller then the gain coefficient for SBS .Also SRS causes coupling in both the direction of propagation and the reverse directions.
In the case of SBS, the pump wave is the signal wave and the Stoke's wave is the unwanted wave that generated due to the scattering process. In the case of SRS. the pump wave is a high-power wave, and the stoke's wave is the signal wave that gets amplified at the pump of the pump wave.
(A)Stimulated Brillouin Scattering (SBS):-
In the case of SBS, the phonons involved in the scattering interaction are acoustic phonons, and the intersection occurs over a very narrow line width. The stoke's and pump waves propagate in opposite directions. Thus SBS does not cause any interaction between different wavelengths, as long as the wavelength spacing is much greater than 20 MHz, which is typically the case SBS can however, create significant distortion with a single channel.
SBS produces gain in the direction opposite to the direction of propagation of the signal, in other words, back toward the source. Thus it depletes the transmitted signal as well as generates a potentially strong signals back toward the transmitter, which must be shielded by an isolator . The SBS coefficient is approximately 4x10 m/w , independent of the wavelength.
(B) Stimulated Raman Scattering (SRS):-
In SRS , if two or more signals at different wavelengths are injected into a fiber, SRS causes power to be transferred from the lower-wavelength channels to the higher - wavelength channels. This coupling of energy from a lower-wavelength signal to a higher-wavelength signal is a fundamental effect that is also the basis of optical amplification and lasers. The energy of a photon at a wavelength is where h is planck's constant
Unlike SBS,SRS is a broadband effect. Its gain coefficient as a function of wavelength spacing. The peak gain coefficient gr is approximately 6x10m/w at 2.55um, which is much smaller then the gain coefficient for SBS .Also SRS causes coupling in both the direction of propagation and the reverse directions.
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