Whether is worth to Use EDFA Amplifier in Long WDM System?

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 Introduction
to EDFA Amplifier

 

EDFA
amplifier, also referred to as erbium-doped fiber amplifier, is basically
composed of a length of Erbium-doped fiber (EDF), a pump laser, and a WDM
combiner. When it works, the pump laser with 980 nm or 1480 nm and the input
signal around 1550 nm can be combined by the WDM combiner, then transmitted and
multiplexed into the Erbium-doped fiber for signal amplification. The pump
energy can be transmitted in the same direction as the signal (forward
pumping), or the opposite direction to the signal (backward pumping), or both
direction together. And the pump laser can also using 980 nm or 1480 nm, or
both. Taking the cost, reliability and power consumption into account, the
forward pumping configuration with 980nm pump laser EDFA amplifier is always
the first choice to enhance the signals for a long WDM system.

 

 

Currently,
utilizing WDM technology to deploy the optical network has received widespread
attentions, which enables higher capacity for data transmission. However, the
technology is also limited by the transmission distance. When deploying a long
WDM system, the signal power would still become weak due to the fiber loss. In
order to address the issue, using EDFA amplifier to directly enhance the WDM
signals would be a good choice for current and future optical network needs.
The optical network combining WDM technology and EDFA module together can
transmit multiple signals over the same fiber, at lengths up to a few hundred
kilometers or even transoceanic distances. To better know how does EDFA
amplifier work in the long WDM system, let’s learn the EDFA
amplifier knowledge and analyze the performance of WDM system bonding
with the EDFA module.

 

Analysis
of WDM Network Without EDFA Amplifier

 

Before
analyzing WDM network deployed with EDFA amplifier, it is necessary to know the
basic configuration of an original WDM network, as shown in the figure below.
We can learn that four signals from different channels are combined by the
optical combiner. And then, the integrated signals are transmitted through an
optical fiber. Thirdly, the signals are split into two parts by the splitter.
One part passes through the optical spectrum analyzer for analyzing signals,
and the other one goes through the photo detector to be converted into
electrical signal and then be observed by the electrical filter and scope.
However, in the process, the signal power gets highly attenuated after being
transmitting at long distance.

 

Analysis
of WDM Network Using EDFA Amplifier

 

By
using the EDFA amplifier, we can easily overcome the attenuation of long WDM
network. From the following figure, we can learn that EDFA amplifiers act as
booster amplifier and pre-amplifier to enhance the signal, so that system will
no longer suffer from losses or attenuation. Therefore, if you need to deploy a
long WDM system, it is highly recommended to deploy the EDFA amplifiers in the
system that features flat gain over a large dynamic gain range, low noise, high
saturation output power and stable operation with excellent transient
suppression. It is an undoubtedly ideal solution with reliable performance and
relatively low cost to extend the WDM network transmission distance.

 

Conclusion

 

It
is well know that the signal power would be greatly attenuated when the
transmission distance is long enough. Hence, when deploying a long WDM network,
it is definitely necessary to use the EDFA amplifier to enhance the signal
strength, allowing for the long transmission distance. As a preferable option,
the EDFA amplifier with very low noise is relatively insensitive to signal
polarization and easy to realize signal amplification.