Since Kao proposed that optical fibers can be used for communication transmission, optical communication technology has flourished along with optical fibers, transforming the world. It can be said that optical fiber is the cornerstone of optical communication technology, and almost all optical transmission technologies now require optical fiber as a transmission medium.
At present, many different types of optical fibers have been developed in the industry for different usage scenarios, but they all have different shortcomings, resulting in poor universality.
The optical fibers currently used for WDM system transmission are mainly single-mode fibers such as G.652, G.655, G.653, and G.654.
● G.652 fiber is restricted in the coherent transmission direction due to its transmission loss and nonlinear characteristics;
● G.655 fiber has strong nonlinear effect due to small fiber dispersion and small effective cross-sectional area, and the transmission distance is only 60% of that of G.652;
● G.653 fiber has serious nonlinear interference between the channels of the DWDM system due to four-wave mixing, and the fiber input power is low, which is not conducive to the transmission of multi-channel WDM above 2.5G;
● G.654 fiber will have a great impact on system transmission due to the multi-optical interference of high-order modes, and at the same time, it cannot meet the requirements of future transmission expansion to S, E, and O bands.
The lack of performance of mainstream optical fibers in the current market also forces the industry to make breakthroughs in new-generation optical fiber technology as soon as possible. LEE, the chief technical planner of the optical product line of Shenzhen Aixton Cable Co., Ltd., takes the next-generation mainstream optical fiber vision as one of the nine major challenges facing the key technologies of optical communication in the next decade. He believes that in order to meet the requirements of constant distance and doubling capacity, and to meet the Moore's Law of light in the development of the wavelength division industry, the next generation of optical fibers must have the following characteristics: First, high performance, low intrinsic loss, and resistance to nonlinear effects Strong capability; the second is large capacity, covering the full or wider available spectrum; the third is low cost, can be engineered, including: easy to manufacture, the cost should be comparable to or close to G.652 fiber, easy to deploy and easy to maintain.
LEE proposed that future technical research directions should include but not limited to hollow-core fibers, SDM fibers, etc.
Commercial projects landed, SDM fiber achieved a major breakthrough
For the optical communication industry, hollow core fiber and SDM fiber are no longer a new concept.
As early as 1979, a similar scheme of SDM fiber has appeared in the industry, and in 1995, the transmission of 1Gbps optical signal within 1km was successfully completed. By 2012, SDM fiber once became a hot spot in the industry. At this time, the application level has reached 305Tbps transmission within 10km. The industry generally regards it as the only way to overcome the fragrant limit of single-mode fiber.
In recent years, with the acceleration of the commercial process of SDM optical fiber and the increase of commercial projects, this once smashing product has reappeared in people's sight. Google took the lead in completing the deployment and testing of the first 12-fiber pair long-distance submarine cable designed with SDM technology, the Dunant submarine cable system, making its transmission capacity in the Atlantic a record 307.2 Tbps, which is also SDM. The first application of the technology on the market. SDM technology enables each pair of fibers to operate with lower optical power and signal-to-noise ratio.
The researchers of the project said that the submarine cable using SDM technology is the future development direction, and SDM technology will make the submarine cable have a larger capacity. Whereas traditional submarine cables rely on dedicated lasers for each fiber pair to amplify the optical signal along the length of the cable, SDM allows the pump laser and associated optics to be shared among multiple fiber pairs.
In addition to Google, other Internet giants such as Facebook and Microsoft are also interested in this technology, and Nokia has vigorously promoted SDM, calling it the only way for the future of optical transmission.