EDFA amplifier is the most common optical amplifier, used for boosting optical signals in optical applications, especially the DWDM systems. It is the key amplification device deployed in the optical system to enhance the signal power, so that the optical transmission distance can be greatly extended. Undoubtedly, the EDFA amplifier is an ideal choice for long-haul DWDM system. But how does it work for extending DWDM system? As shown in the following figure, EDFA amplifier can be placed at the transmitting side of the DWDM link, any intermediate point along the transmission DWDM link and the receiving end of the DWDM link, separately working as booster amplifier (or post-amplifier), in-line amplifier (or optical line amplifier) and pre-amplifier for optimizing the DWDM system reach. Let’s study the related knowledge in details.

EDFA amplifier is a kind of optical amplifier that can directly amplify any input optical signal without the need of optical-electrical-optical conversion. It can not only save the cost for long-haul transmission, but also reduce the signal loss and unwanted noise, compared to the traditional optical-electrical-optical amplification. As the fiber attenuation limits the reach of a non-amplified fiber link to about 200 km, EDFA amplifier is an ideal choice for building wide area purely optical networks.

As mentioned before, EDFA amplifier can be deployed in three places of the DWDM link to make the power compensation, the transmitting side of the link, the intermediate point along the link and the receiving end of the link. If placed at the transmitting side, it can be called as booster optical amplifier or post-amplifier, offering high input power for the wide fiber span. If placed at the intermediate point along the link, you can call it in-line amplifier or optical line amplifier. The optical line amplifier is used for compensating the fiber loss in the transmission link. When you call it pre-amplifier, it must be deployed in the receiving end, for boosting the signal power to the the necessary receiver level. The following will introduce these three different deployments of EDFA amplifier and how does the it work in the three link.

Placed at the Transmitting Side: in this application, we always call EDFA as booster optical amplifier that features high input power, high output power and medium optical gain. It can directly amplify the aggregated optical input signal multiplexed by the DWDM Mux Demux, to achieve DWDM network transmission distance extension. By placing the EDFA amplifier at the transmitting side of the DWDM link, the transmitted signal power can be enhanced to the necessary transmitting level and the optical loss caused by the laser and optical fibers can be also compensated. Hence, the EDFA booster optical amplifier is always deployed when the DWDM Mux Demux attenuates the signal channels.

Placed at the Intermediate Points: as shown in the figure below, the EDFA in-line amplifier can be put at any intermediate point along the long transmission link. This kind of EDFA optical amplifier is designed with low input power, high output power, high optical gain and low noise figure, which are normally deployed every 80-100 km to amplify signals between any two link nodes on the main optical link, with the aim of compensating the loss caused by fiber transmission and other factors. Thereby, the optical signal level can stay above the noise floor.

Placed at the Receiving Side: EDFA optical amplifier operates at the receiving side of the link is also referred to as pre-amplifier, which has the features of medium to low input power, medium output power and medium gain. This optical pre-amplifier put before the receiver end of the DWDM link is to compensate for losses generated by the demultiplexer located near the optical receiver. With the use of pre-amplifier, the optical signal level can be enhanced before the photo detection, hence improving the receive sensitivity for a long-haul fiber DWDM link.

In conclusion, the EDFA optical amplifier can be deployed as booster optical amplifier in the transmitting side of the DWDM link to provide high input signal power for the wide fiber span. It can also work as in-line amplifier at the intermediate point along the link for compensating the fiber loss in the transmission link. What’s more, as the pre-amplifier deployed in the receiving end, it amplifies the signal power to the the necessary receiver level. No matter where the EDFA optical amplifier is deployed in the DWDM link, the signal power can be always enhanced for making a longer DWDM system.

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