optical transmission system

400G High-Speed Optical Transmission System

This paper analyzes the development background of 400 G optical transmission technology and the main factors affecting the transmission performance of 400 G system; analyzes the technical approach to realize low-loss single-mode fiber, and designs and develops a new type of single-mode fiber suitable for high-speed optical transmission.

Technologies such as mobile Internet, 4K, cloud computing, Internet, home broadband, and the Internet of Things are developing at a high speed. Driven by strategic policies such as “Internet +”, “Speed ​​Up and Fee Reduction”, “One Belt and One Road” and “Broadband China”, along with 4G The application of 5G/5G and the popularity of smartphones have led to the continuous increase of wired access and wireless access bandwidth, and the data traffic (information) has shown an avalanche growth.

It can be seen that the development direction of the optical fiber backbone transmission network is an ultra-high-speed, ultra-large capacity, and For ultra-long distances, the transmission rate of the optical communication system will be developed from 10G/40 Gbit/s to 100G/400 Gbit/s, and then to 1 T/2 Tbit/s to meet people’s increasing bandwidth demand.

From 2014 to 2015, 100G optics began to be commercialized on a large scale. At present, China has become the market for the large-scale application of the global 100G optical transmission technology.

400G has become the typical rate of high-speed transmission standards designated by the three major international standard organizations, ITU, IEEE and OIF, and the research and application of 400G high-speed optical transmission technology has become one of the important research contents of the industry.

400G high-speed optical transmission system

Facing the explosive growth of various customers and mobile Internet traffic, the telecom operator China Mobile proposed the strategy of “crossing 40G and directly introducing 100G/400G” to meet the needs of the telecom market.

 In 400 G high-speed optical transmission technology, nonlinear effects, fiber attenuation, dispersion and polarization mode dispersion become the main factors of system transmission performance.

The Shannon’s law of the optical transmission system indicates that the higher the spectral efficiency (Spectral Efficiency), the greater the capacity, and the greater the optical signal-to-noise ratio (OSNR) under a certain bit error rate, which further limits the optical transmission distance (the transmission distance decreases sharply).

Non-linear effects caused by wavelength division multiplexing/dense wavelength division multiplexing (WDM/DWDM) systems limit the signal input power, thereby limiting the optical signal-to-noise ratio and further increasing the technical difficulty of improving spectral efficiency.

How to realize a high-speed transmission system with high spectral efficiency (large capacity) and long distance, and maintain low cost is the biggest challenge for a 400G/1T/2T optical transmission system.

DSP and coherent detection (reception) have become the main technologies to solve dispersion and polarization mode dispersion. Increasing the mode field area has become the nonlinear effect of reducing high-speed signal transmission. Designing and manufacturing ultra-low loss optical fibers and reducing ASE noise accumulation introduced by optical amplifiers are the same New single-mode fiber for distance links can bring equivalent system gain.

New optical fiber

The production capacity of ordinary single-mode optical fiber for communication is relatively surplus, and the trend is the commercialization of ultra-low loss, large effective area single-mode optical fiber, and multi-core single-mode optical fiber. Research on new fiber optics shows two “low” and two “new”.

That is, low loss, low cost, new materials, and new processes. For attenuation suppression, PCVD deep-doped fluorine technology is used, and for preform manufacturing, a nonlinear combination of deposition flow is used.

At present, the attenuation coefficient of conventional single-mode fiber (G. 652) is about 0. 185 dB/km (1550 nm), the effective area is small, and it cannot meet the technical requirements of 400 G/1 T high-speed optical fiber communication. Research and develop new types of optical fibers with parameters such as ultra-low attenuation and large effective area to meet the needs of high-speed optical fiber communication systems.

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