1. Erbium-doped Fiber Amplifier, due to multiple cascades and the accumulation of noise caused by spontaneous emission, will reduce the system CNR greatly and thus it will limit the transmission capacity and distance of the system. Raman Fiber Amplifier (RFA) is a newly designed fiber amplifier based on Stimulated Raman Scattering (SRS) effect. It is considered as the core technology of new generation DWDM fiber over-long communication. Compared with Erbium-Doped Fiber Amplifier, Raman amplifier has the advantage of low Noise Figure (NF), wider gain bandwidth, flexible gain spectral region and stable temperature. It is the only device that can operate in 1300~1600nm.
2. The gain medium of EDFA is Erbium-doped Fiber (EDF). It is a separated amplifier and its signal light can only be amplified after putting into EDFA. The gain medium of Distributed Raman Amplifier is Single Mode Fiber (SMF) which is for signal light transmission. Its gain area is distributed at long transmitting fiber that is 25km from the output end. That is to say, the signal light is amplified 25km before it reaches the output end of the transmitting fiber.
3. Low noise figure marks the super advantages as following:
① During Single Mode Fiber(G.652) transmission, adopting Distributed Raman Amplifier, it can reduce the loss for 5.5dB (Typical value) at effective cross-distance. Compared with EDFA, it equals that the effective distance is reduced for 25km, (fiber loss is calculated as 0.22dB/km). Therefore, the input power to the fiber is reduced and the damage of fiber non-linearity effect (SBS) is weakened.
② In OSNR calculation, the Equivalent Noise Figure of distributed backward pump Raman Amplifier is 0dB, typical value 0 ~ -2dB, which has remarkable help for improvement of cross-band length, increase system OSNR and transmission distance.
4. But Raman amplifier also has its disadvantages. Its gain is very low, not exceed 16 dB in actual application. Although the noise figure of EDFA is incomparable with Raman amplifier, its small signal gain can be higher that 30dBm. So the Raman amplifier is always combined with EDFA in system application. Hybrid Raman Amplifier combined both the two amplifier is an idea solution.
When an backward EDFA (If GP=10dBm, NF=5.5Db) combines with one pre-distributed Raman Amplifier (if GP=10dB, NF=-0.5dB), the gain of hybrid Raman amplifier (Raman + EDFA) will reach to GP=200Db and NF=0.96dB.
5. Huatai HFA5000 is a combination of RFA and EDFA to get flat Gain spectrum and high Optical Signal Noise Ratio (OSNR) . The un-relayed distance can be extended up to 30~50km and CNR can be improved for 4.5~6dB.
Perfect laser APC, AGC, ATC closed-looped circuit ensuring long life and stable operation of the pump laser.
Low noise figure and flat gain.
Adopts famous Fitel Raman pump laser.
Different raman gain and EDFA output power optional ， be suitable for different network.
Optimized structure, easy to use.
Fiber CATV system, extra-long trunk that is inconvenient for building relay station .
Relay distance > 60Km.
Single span distance > 80Km.
DWDM, CATV extra-long trunk optical transmission system.
Submarine optical transmission system.