For optical fiber communication, ultra-high speed, ultra-large capacity and ultra-long-distance transmission have always been the goals pursued by people, and all-optical network is also the dream that people pursue unremittingly.

     1. Ultra-large capacity, ultra-long-distance transmission technology WDM

The technology has greatly improved the transmission capacity of the optical fiber transmission system, and has broad application prospects in the future cross-sea optical transmission system.

     In recent years, the wavelength division multiplexing system has developed rapidly. At present, the 1.6Tbit/WDM system has been commercialized in large quantities, and the all-optical transmission distance is also greatly expanded. Another way to increase transmission capacity is to use optical time division multiplexing (OTDM) technology. Unlike WDM, which increases its transmission capacity by increasing the number of channels transmitted in a single fiber, OTDM technology increases transmission capacity by increasing the rate of a single channel. , the single-channel maximum rate achieved by it reaches 640Gbit/s.

     Only relying on OTDM and WDM to improve the capacity of the optical communication system is limited, after all, multiple OTDM signals can be wavelength-division multiplexed, thereby greatly improving the transmission capacity. Polarization Multiplexing (PDM) technology can significantly reduce the interaction of adjacent channels. Since the return-to-zero (RZ) encoding signal occupies a small space in the ultra-high-speed communication system, the requirements for the dispersion management distribution are reduced, and the RZ encoding method has a strong adaptability to the nonlinearity of the fiber and the polarization mode dispersion (PMD). Therefore, the current ultra-large-capacity WDM/OTDM communication systems basically use the RZ encoding transmission method. The key technologies that need to be solved in the WDM/OTDM hybrid transmission system are basically included in the key technologies of OTDM and WDM communication systems.

     2. Optical soliton communication. Optical soliton is a special ultra-short optical pulse of ps order. Because it is in the anomalous dispersion region of the fiber, the group velocity dispersion and nonlinear effects are balanced with each other, so after long-distance transmission through the fiber, the waveform and speed remain unchanged. Optical soliton communication is to use optical soliton as a carrier to realize long-distance and distortion-free communication, and the information transmission can reach thousands of miles under the condition of zero bit error.

     The future prospect of optical soliton technology is: the use of ultra-long-distance high-speed communication in terms of transmission speed, ultra-short pulse control technology in time and frequency domains, and ultra-short pulse generation and application technology to increase the current rate of 10-20Gbit/s to 10Gbit/s. More than 100Gbit/s; in terms of increasing the transmission distance, retiming, shaping, regeneration technology and reducing ASE are used, and optical filtering increases the transmission distance to more than 100,000km; in terms of high-performance EDFA, it is to obtain low-noise and high-output EDFA. Of course, there are still many technical difficulties in the actual optical soliton communication, but the breakthrough progress that has been made so far makes people believe that the optical soliton communication is in the ultra-long distance, high-speed, large-capacity all-optical communication, especially in the submarine optical communication system. Has bright development prospects.

     3. All-optical network. The future high-speed communication network will be an all-optical network. The all-optical network is the highest stage in the development of optical fiber communication technology, and it is also an ideal stage. The traditional optical network realizes all-opticalization between nodes, but electrical devices are still used at the network nodes, which limits the further improvement of the total capacity of the current communication network trunk line. Therefore, the true all-optical network has become a very important topic.

     The all-optical network replaces electrical nodes with optical nodes, and the nodes are also all-optical. Information is always transmitted and exchanged in the form of light. The switch does not process user information by bits, but determines routing based on its wavelength.

     At present, the development of all-optical network is still in its infancy, but it has shown good development prospects. From the perspective of development trend, forming a real optical network layer based on WDM technology and optical switching technology, establishing a pure all-optical network, and eliminating electro-optical bottlenecks have become an inevitable trend in the development of optical communication in the future, and more importantly, the future information network. It is also the highest level of communication technology development, and it is also the ideal level.