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Brief Introduction of Optical Line Protection

Updated on June 23, 2019

The particularity of optical transport network (OTN) requires that optical transmission equipment and lines must have high stability and security. However, problems like optical fiber damage, line interruption, and equipment power down always severely affect the security of OTN. Then, what should we do to protect OTN security? Luckily, the appearance of optical line protection (OLP) system has provided one of the effective solutions. This article will have a brief introduction of OLP and its working methods.

What Is Optical Line Protection?

Optical line protection (OLP) is a device used in pairs to protect network transmission lines. When the power value of a working fiber is lower than a certain lever, OLP can automatically switch from the working fiber route to another spare fiber route by real-time monitoring. It is usually used with devices such as DWDM mux, EDFA, and DCM to achieve fiber expansion in optical transport network. Due to its high security and service quality, OLP is widely used for protecting backbone and important business line.

Common Methods of Optical Line Protection

In optical transport network, there are two common types of optical line protection: OLP 1:1 system and 1+1 system, which can meet requirements of different applications. The following part will introduce the working methods of OLP 1:1 and OLP 1+1.

OLP 1:1

The 1:1 optical line protection system adopts a selective transmitting and selective receiving method. There are two fiber routes: primary path and secondary path. The optical power sent from Tx port will be normally transmitted through the primary path. When Rx port detects the power valve of primary path is decreasing, OLP 1:1 system will automatically switch the transmitting power and receiving power from the primary path to secondary path. This OLP 1:1 system has low insertion and high security, which is mainly suitable for trunk/local OTN and dedicated line customers.

OLP 1+1

Unlike OLP 1+1 system, optical line protection 1+1 system is based on dual transmitting and selective receiving method, which means the power can be transmitted through two paths at the same time. The optical power from Tx port will be divided into two equal parts on the primary path and secondary path. No matter what fault happens in single Tx or Rx direction of neither path, the two paths are still in use. This OLP 1+1 system has low cost and fast switching speed. However, because of its high insertion loss, OLP 1+1 is more suitable for short distance transmission with large surplus of the line.

Advantages of Optical Line Protection

From the introduction above, we can know that OLP can realize optical power monitoring and automatic switching. The following part will focus on these two advantages.

Real-Time Power Monitoring

OLP system can provide real-time monitoring of the primary and secondary optical fibers, which can effectively avoid the simultaneous block of the two optical fibers. This real-time power monitoring improves the transparency and security of optical transport network.

Automatic Switching

When the current optical power is lower than normal value on the main fiber, the system will automatically switch to the secondary available fiber, so as to ensure the smooth flow of the service. It can shorten the interruption time and improve the efficiency of maintenance.


Like the devices of DWDM mux, EDAF, and CDM, OLP is also an essential part of optical transport network. OLP has established a strong protection mechanism in place for network, which makes optical transport network with no-block, high reliability, safety, and high anti-disaster strength.


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