General Information
Chapter 4
Amplifier Modules
General Information 63
AM-S20H-2 65
General Information
Overview 63
Naming Conventions 64
Overview
Light signals transmitted in DWDM networks over multi-kilometer fiber-optic links are
subject to attenuation due to fiber loss and component insertion losses. Optical amplifiers
(OAs) are used in such networks to reconstitute attenuated optical signals. Therefore,
OAs are key devices in DWDM networks that allow expanding the effective fiber span
between the data source and the destination without the need for repeaters at
intermediate points.
Optical amplification is typically performed by erbium-doped fiber amplifiers (EDFAs) and
distributed Raman fiber amplifiers (Raman amplifiers). EDFAs and Raman amplifiers
differ in their operating principles.
The primary operating principal for EDFAs is its local amplification based on the use of
special Erbium-doped fiber. The gain medium of an EDFA is several meters of Erbium-
doped fiber that is pumped by either 980-nm or 1480-nm pump lasers. Incoming light of
longer wavelengths, in the 1550-nm range, is amplified within this fiber. Both the C-band
and the L-band can be amplified by EDFAs, but two different amplifiers are required, each
optimized for the band of interest.
Generally several types of EDFA designs are offered with each design being customized
for different purposes. Examples of customization are: gain and tilt ranges (high gain or
low gain), variable gain or fixed gain, maximum output power levels, band (C-band or L-
band), and band range (or passband).
The primary operating principal for Raman amplifiers is the use of the transmission fiber
itself as the gain medium. Data signals transmitted over this fiber are optically amplified
by multiplexing a powerful pump wavelength with signal wavelength (stimulated Raman
scattering effect). Optical signal amplification is distributed several kilometers along the
transmission path. A Raman amplifier is typically stationed at the end of a transmission
FSP3000 C Hardware Guide - R1.1 - Issue:A (12/09/2016) 63
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