Transmission distance has always been a key factor during deployment of fiber optic network. DWDM technologies, which are considered as the most cost-effective ways to increase the network capacity over long transmission distance, have been widely applied in our telecommunication network. To further extend transmission distance of optical signals transmission from the DWDM fiber optic transceivers, optical amplifiers are usually used in the DWDM network. Different types of optical amplifiers have been invented to meet the signal amplifying requirements at different situations. This post will introduce the differences between the three most commonly used optical amplifier: pre-amplifier, booster amplifier and in-line amplifier.Basics of Optical Amplifier
In the past, if you want to extend the transmission distance of DWDM network, optical regenerator station is required to be installed in the fiber link every 80km to 100km. The regenerator station will electronically regenerate the optical signals to overcome the power loss and ensure that the optical signal can be detected at the receiver end. However, this requires a lot of money and is not easy to upgrade the whole network.
With optical amplifier, things become much easier. The optical amplifier can enlarge the optical signals without the regeneration. In addition, the network upgrading is more cost-effective with optical amplifier. Each optical amplifier has an important factor which is operation gain measured in dB. The operation gain of the optical amplifier should be carefully calculated to ensure the network performance. Pre-amplifier, booster amplifier and in-line amplifier are used in different places in the fiber optic network. And they support different operation gain according to the whole network requirement.Pre-Amplifier, Booster Amplifier and In-line Amplifier
Pre-Amplifier is usually installed at the receiver end of the DWDM network to amplify the optical signal to the required level to ensure that it can be detected by the receiver. The following picture shows a typical diagram for a duplex 10G DWDM network which can support 80km. A pre-amplifier is installed at each receiving end of this network. There will be great power loss after the optical signal goes through the 80km optical fiber. Then, pre-amplifier installed at the receiver end is necessary. Generally, a pre-amplifier should offer high gain to ensure that the optical signal is detectable.
Booster Amplifier is installed in the transmitting end of the fiber optic network, which can amplifier the amplify the optical signal launched into the fiber link. It is usually used in DWDM network where the multiplexer attenuates the signal channels. The following picture shows a 10G DWDM network using booster amplifier (BA) at the transmitting end and pre-amplifier (PA) at receiving end. Thus, this 10G DWDM network can support a transmission distance much longer than the above mentioned one. Please note, a DCM (Dispersion Compensation Module) is added in this network to further ensure the transmission quality. A booster amplifier usually provides low gain and high output power.
In-line Amplifier is easy to understand. The gain provided by the pre-amplifier and booster amplifier might not be enough due to the optical loss caused by long haul transmission. In-line amplifier is installed in the fiber optic link every 80-100km as shown in the following picture. It has moderate gain and has similar output power to those of booster amplifier.
Optical amplifier can help to amplifier the optical power during long haul transmission to ensure that the receiver can detect the optical signal without error. Three amplifiers are commonly used in DWDM network. Booster amplifier is used to amplifier optical power at the transmitting end and pre-amplifier is placed at the receiver end. If the transmission distance is longer than 150km or have great power loss during transmission, in-line amplifier is suggested to be installed every 80km to 100k in the fiber optic link.