Written by: Reporter Yan Tao from "China Science Daily"
Zhang Xingyong
In one of China's four great classical novels, "Journey to the West," Sun Wukong possesses a magical spell called the "Water Avoidance Technique." The 43rd chapter of the book states: "The Monkey King used the Water Avoidance Technique to separate the waves." By reciting this spell, Sun Wukong can freely traverse the water without hindrance.Now, the plot of "Journey to the West" is becoming a reality. Recently, China's first set of deep-sea optoelectronic composite underwater wet pluggable connectors, jointly developed by the Xi'an Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences (CAS), the Institute of Acoustics of CAS, the Shenyang Institute of Automation, the Changchun Institute of Applied Chemistry, and the Laoshan Laboratory, has passed acceptance evaluation and has been successfully running in 1620-meter-deep waters for over 70 days. This wet pluggable connector can achieve a "watertight" seal according to requirements, withstand high water pressure and corrosion, and, just like reciting the "Water Avoidance Technique" incantation, enable the transmission of optical and electrical signals in the deep sea.Successful deep-sea trial deployment."Running Naked" in the deep sea without a single leak
Why is it called a "wet pluggable connector"? Wu Guojun, the head of the equipment development and director of the Marine Optics Technology Research Department at the Xi'an Institute of Optics and Precision Mechanics, explains that this underwater wet pluggable connector is divided into two parts, similar to household electrical plugs and sockets. During underwater construction projects, no waterproof measures are taken. Instead, one end is fixed underwater using facilities such as connection stations, and then the other end is inserted to establish the connection."During the docking process, it is necessary to ensure the optical and electrical conductivity and maintain a 'watertight' seal, which means no water leakage. After a successful connection, it is essential to maintain the 'watertight' seal for long-term operation," says Wu Guojun. Therefore, ensuring that the connector remains leak-free while "running naked" in the deep sea is crucial.Because the core diameter of the optical fiber in the connector is very small, at only 9 micrometers, any suspended particles in the water can interfere with the connection. Even an error of just 1 micrometer can cause significant fiber optic communication loss, resulting in failure. Ensuring the synchronization and high-precision docking of multiple fiber optic channels in the deep sea is the core issue that the team needs to solve.Wu Guojun and his team have established a completely "watertight" channel throughout the entire docking process to ensure smooth passage of the optical fiber from one side and docking with the other side's optical fiber.Wu Yafeng, the deputy director of the Marine Optics Technology Research Department at the Xi'an Institute of Optics and Precision Mechanics, explains that the team solves this problem by using oil immersion. "First, we fill the sealed box with special silicone oil to ensure that the external pressure and internal silicone oil pressure are balanced, avoiding direct exposure to high pressure in the deep sea. Filling the sealed chamber with silicone oil also helps protect the optical fibers and electrical contacts from direct contact with seawater," said Wu Yafeng.According to researchers, large-scale underwater projects cannot be built as a whole and must be assembled piece by piece. For example, when laying submarine optical cables, multiple connection stations, main stations, junction boxes, and beacons need to be connected to the fiber cable. Therefore, the deployment needs to be carried out separately."We can first deploy the part with the wet pluggable connector plug, then deploy the other end, and finally provide power source and signal acquisition transmission by connecting through the wet pluggable connector. Without it, many of our large-scale deep-sea projects would be impossible," Wu Guojun told "China Science Daily."Wu Guojun (second from left) and his team at work.Putting a motorcycle on a fingernail
According to relevant data, the deepest recorded scuba dive by a human equipped with diving gear is 332 meters. However, wet pluggable connectors work in depths exceeding 1,000 meters, far beyond the limit of human interaction. Therefore, ROV (Remotely Operated Vehicle) manipulator arms are essential for operation. When the wet pluggable connectors are being plugged and unplugged, the manipulator arm can push one end into the other end through a handle reserved at one end of the connector to achieve connection.Operating in the deep sea is much more challenging than on land. In addition to requiring a "watertight" seal during the connection process, it is crucial to ensure that the insertion force of the manipulator arm is not too high. However, the challenge does not end there; achieving precision is the biggest problem faced during deep-sea underwater connection.An optical fiber achieves a connection accuracy of 9 micrometers, but the precision of the operator is not that high. This requires a certain amount of redundancy in the operation, with multiple stages of guidance implemented to achieve accurate docking through simple operations.In the beginning, the team observed leakage in shallow water, where the pressure was relatively low and the risks were relatively low. However, as the pressure increased, so did the friction. The connector is a "dynamic seal" underwater and must solve the problems of both pressure and friction. This is the aspect that Wu Guojun and the team have found particularly challenging.It is impossible to simulate this state in shallow water. In order to carry out experiments, the team developed a set of plugging and unplugging devices different from the manipulator arm. This device secures the connector on a linear guide rail, ensuring higher docking accuracy, and can be placed in a pressure vessel to simulate the plugging and unplugging process under specific pressure.
