Raman fiber amplifier (RFA) is an important part of dense wavelength division multiplexing (DWDM) communication system.
In many nonlinear optical media, the scattering of pump light with a shorter wavelength causes a small part of the incident power to be transferred to another beam whose frequency is shifted down. The amount of frequency shift down is determined by the vibration mode of the medium. This process is called pulling Mann effect.
If a weak signal and a strong pump light wave are simultaneously transmitted in the fiber, and the weak signal wavelength is placed within the Raman gain bandwidth of the pump light, the weak signal light can be amplified. This mechanism is based on stimulated Raman scattering The optical amplifier is called RFA.
advantage
Compared with other different types of optical amplifiers, Raman fiber amplifiers have many advantages:
(1) It is very different from EDFA. RFA does not require special gain media. As long as ordinary transmission fiber can achieve optical signal amplification, it can achieve distributed amplification and direct expansion and upgrade of fiber amplification system. Reasonable use of optical fiber's low loss window and other related improvements.
(2) The wavelength of the gain light of the Raman amplifier depends on the wavelength of the pump light. In theory, as long as the appropriate wavelength of the pump light is selected, any optical signal band can be amplified to achieve full-band Raman amplification.
(3) The Raman gain of the optical fiber has a relatively wide frequency band. If the optical fiber Raman amplifier of the multi-wavelength pumping mode is adopted, it can be more than
100nm gain spectrum.
(4) Low noise figure. The hybrid amplifier of EDFA and RFA can greatly improve the performance of the transmission system.
(5) The gain spectrum of the Raman fiber amplifier has a superposition effect. The multi-pump method can obtain a wider Raman gain spectrum, and the Raman gain spectrum of a single wavelength will compensate each other, so as to achieve the effect of gain flatness. , To ensure the stability of signal transmission.
(6) The saturation power is very high. When the amplified signal power begins to approach the pump power, the decrease in optical gain is only 3 dB.
Many of the above advantages also determine that Raman fiber amplifiers can be widely used in WDM fiber communication systems.
Disadvantage
(1) Insufficient gain bandwidth;
(2) Low output gain;
(3) The output gain is not flat.