With the rapid development of data communications and Internet, the network point-to-point, online applications and video services have all experienced explosive growth. Massive digital media content has caused a ten-fold or even one hundred-fold rapid increase in Internet traffic, which has led to telecommunications. The traffic of the backbone network is increasing rapidly at a rate of 50% to 80% every year, causing the bandwidth cost of the operator to increase continuously. It is necessary to increase the entire network capacity to meet the increase in service requirements and reduce the transmission cost per bit. Currently, 100G systems are already in commercial use by major carriers. The 400G system can further increase network capacity and reduce transmission cost per bit on the basis of 100G, effectively solving the pressure on service providers to face continuous growth in service traffic and network bandwidth. It is expected to be in 2017. Around the year will also begin to gradually commercial.

The PM-QPSK modulation technology, coherent detection technology and DSP processing technology used in the 100G system reduce the OSNR tolerance of the system to the same level as 10G, which reduces the requirements of the system to the optical fiber. Studies have shown that under the 100G system ordinary G.652D fiber, low loss and ultra-low loss fiber can transmit more than 1000km distance; ultra-low loss can extend the link distance 35-40%, some lines can reduce the relay station, which is good for the whole Optical network construction; In some systems with ~100km long-distance optical sections, ULL fiber can effectively reduce span loss.

Problems such as OSNR limitation, noise, and nonlinearity brought by the 400G transmission system will limit the transmission distance. From the test results of current mainstream equipment manufacturers, the transmission distance of the 400G system with dual carrier and 16QAM modulation technology is only 100G. About 1 / 3, so the construction of high-speed systems need to consider the system capacity and transmission distance requirements. From the perspective of line-side transmission equipment, multi-carrier light sources, high-order modulation, coherent detection, high-speed DSP systems, and error correction techniques can be used to promote the development of commercial high-speed optical transmission systems. The system OSNR can be improved and the transmission distance can be effectively extended, which can reduce the use of electrical relays, optimize the network structure, and save construction