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Dear Ehab,
Thank you for asking me this question.
EDFAs could be used in a single or double stage setup in metro, long haul, and ULH networks; while Raman complements EDFA for LH & ULH systems. The advantages of using the EDFA double stage setup are:
· Providing high gain/low noise at the first stage with980nm pump laser (low NF) and high power output on the1480nm pump laser second stage
· Ability to place a loss element (DCU, OADM, gain flattening amplifier) between the stages without degrading the overall performance effectively
· Redundancy
The critical consideration in using RAMAN is the requirement to provide amplification in the S & U bands. However, the associated challenges are: requiring high & constant pumping power level (producing nonlinearities) and crosstalk among wavelengths (could be treated).
I hope this answers your inquiry.
Regards
Khaled
EDFA can only amplify forward direction.
RAMAN amplifier can amplify both forward and backward direction.
RAMAN amplifiers are mainly used in long distances.
Dear Ehab,
The EDFA and Raman amplifiers are based on two different physical phenomenons.
The main difference between these two techniques is related to the gain medium where the amplification of signal takes place. In the case of EDFA, the amplification occurs in the Erbium doped fiber located within the closed amplification module so EDFA are classified as lumped amplifiers. While the Raman amplification occurs in the transmission fiber itself so unlike EDFAs it is a distributed amplification.
The Raman amplification can extend the maximum transmission reach of an optical system as it has a very low Noise Figure (negative Noise Figure compared to4 or5 dB for EDFAs).
The Raman spectrum gain depends only on pump wavelength. The maximum gain is occurring about100nm higher than the pump wavelength. So as Mr. Khaled said it can provide amplification in the S & U band.
I hope this is helpful for you
Abdul Rahman
