EDFA Amplifiers for Building Long-haul DWDM Networks

Clearly different from the traditional repeater, the EDFA amplifier doesn’t need to convert the optical signals into electrical ones, then make the electrical amplification and finally convert the amplified electrical signals into amplified optical signals again. It is an optical amplifier that can directly enhance the optical signals without making additional conversion. By using the EDFA optical amplifier, the attenuated signal power can be amplified into strong signal level to meet the requirement of the long-haul applications, especially the long-haul DWDM networks. To better understand the function of EDFA amplifier, the following will mainly study the working principle of EDFA amplifier works and illustrate how to use it to build the long DWDM network.

What’s the Working Principle of EDFA Amplifier?

From the figure below, we can learn the basic configuration of the EDFA amplifier, mainly composed of a length of EDF (erbium doped fiber), a pump laser with 980 nm or 1480 nm, a pump combiner and a simple WDM system. When the attenuated signals around 1550 nm pass through an EDFA amplifier, a pump laser will be generated. Then the DWDM signals and pump laser will be combined by the pump combiner. When they come into the EDF together, the wavelengths of signals and pump laser will be multiplexed and the interaction with the doping ions would enhance the signal power into high level. Thereby, a longer DWDM transmission can be reached.

How to Use EDFA Amplifier for Long DWDM network?

In a long DWDM network, the EDFA amplifier can be put in three different places with different aims. Firstly, we can put it in the transmitter side of the DWDM link to offer high input signal power, so that the DWDM fiber link can be extended. If the EDFA amplifier is deployed in this place, we can also call it EDFA optical booster amplifier. Secondly, we can also place the EDFA amplifier in the receiver side of the DWDM link as optical preamplifier, hence the output signal power can be boosted to meet the necessary receiver level. Finally, when the fiber loss in the transmission process is too high to support the long DWDM network, we can deploy the EDFA amplifier in any intermediate point along the long fiber link to compensate the fiber loss. And this time, we can call it EDFA optical in-line amplifier.

Analysis of Practical Long DWDM Cases with EDFA Amplifiers

Case One: in this case, EDFA optical booster amplifiers are deployed at both transmitter sides of the dual-way DWDM links. We can learn it from the figure below. Two 40 channel DWDM Mux Demux are deployed to multiplex 40 1G signals. Then the two integrated 40G signals from both sides are enhanced by the booster amplifier and can be transmitted up to 170 km over each single fiber.

Case Two: as shown in the following figure, except for the booster amplifiers, EDFA optical optical preamplifiers are also placed at both receiver sides of the dual-way DWDM links. By adding the optical preamplifiers to the CWDM link, the transmission distance is finally extended from 170 km to 200 km.

Case Three: it is highly noted from the following figure that the DWDM transmission distance can be up to 400 km. How to achieve this? Just putting the EDFA amplifiers in the three places mentioned above. As deployed in the figure, a pair of EDFA optical booster amplifiers, optical preamplifiers and optical in-line amplifiers are used for the 400km transmission.

Case Four: If the distance of 400 km still cannot meet our requirement, we can set up more repeater sites to place other optical in-line amplifiers. At present, using these three kinds of EDFA amplifiers already enables 100Gbps bandwidth for realizing up to 1000 km in a point-to-point connection, as shown in the figure below.

Conclusion

When designing a long-haul DWDM network for transmitting big data, EDFA amplifier is an ideal solution for current and future optical system which should be taken into consideration. It can be deployed at the transmitter side, the receiver side and any intermediate point along the DWDM long fiber link, as optical preamplifier, booster amplifier and in-line amplifier, for enhancing the signal power, thereby a long-haul transmission can be deployed.

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.