Whether to Use EDFA Amplifier in Long WDM System Or Not?

---

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.

 

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.

 

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.