Hi,
An erbium-doped optical fiber amplifier (EDFA) is a typical rare-earth-dope OFA.
An optical fiber amplifier (OFA) is a component for improving optical signal strength, which can be classified into a rare-earth-dope OFA and a non-linear OFA. In a rare-earth-dope OFA, doped ions in fibers transit to a sub-stable high-excitation state after being excited by pump light. In this way, stimulated radiation is generated and coherent amplification is performed on the signal light.
Classification of EDFAs
Classification of Raman Amplifiers
Based on the position of the Raman amplifier on the fiber line, Raman amplifiers are classified into forward Raman amplifiers and backward Raman amplifiers.
| Type | Description |
|---|
| Forward Raman | Forward Raman amplifiers are placed at the transmit end of the line side and behind a high power EDFA. |
| Backward Raman | Backward Raman amplifiers are placed at the receive end of the line side and must be followed by an EDFA. |
According to the composition of Raman amplifiers, Raman amplifiers can be classified into independent Raman amplifiers and hybrid Raman amplifiers.
| Type | Description |
|---|
| Independent Raman amplifier | Early forward Raman amplifiers and backward Raman amplifiers are generally independent Raman amplifiers. Typically, an independent Raman amplifier installed in an independent subrack. The gain is about 10 dB to 20 dB. |
| Hybrid Raman amplifier | The Raman amplifier and the EDFA form a hybrid amplifier, which is integrated in a board. The gain range of the hybrid amplifier can cover each range from 20 dB to 50 dB. |
As technology develops, independent Raman amplifiers have been gradually replaced by the integrated hybrid Raman amplifiers.
Comparison Between EDFA and Raman Amplifiers
Both the EDFA and Raman amplifiers feature high gain, low noise figure, and high output power. The following table lists the differences between the two types.
| Item | EDFA | Raman Amplifier |
|---|
| Gain wavelength | Fixed range. The operating wavelength is within the 1550 nm window. | Gain exists in any fiber regardless of the fiber type. The gain wavelength is determined by the pump wavelength. Theoretically, signals of any wavelength can be amplified. |
| Stability | Stable. The EDFA is insensitive to temperature. The gain has little correlation with polarization and is irrelevant to the system bit rate and data format. | Unstable and strong polarization-dependent gain. The orthogonal pump mode, transient gain, and backward pump mode are used. |
| Gain bandwidth | Unflatness | Flatness within the gain bandwidth range |
| Cost | Moderate | Relatively high |
| Precautions | The optical surge problem of the EDFA is severe. The peak optical power may reach several watts, which may damage O/E converters and optical connectors. Therefore, it is not recommended EDFAs be cascaded. | The output optical power of the Raman amplifier is high. During maintenance, do not look into the optical port without eye protection. The laser of the Raman amplifier must be shut down before the board with fibers is removed. Otherwise, the maintenance personnel may be injured by strong light. |
https://info.support.huawei.com/network/ptmngsys/Web/WDMkg/en/34_edfa_raman.html
Hope it helps!
