On July 8, the project "Key Technologies and Applications of Ultra-Long Span Optical Communication in Extreme Environments," led by Beijing University of Posts and Telecommunications and jointly completed by China Telecom, Zhongtian Technology, and Accelink Technologies, won the second prize of the 2025 National Technological Invention Award. Targeting areas where dense communication stations are difficult to deploy, such as high-altitude cold regions and deep-sea areas, the project systematically tackled challenges in optical fiber cables, optical amplification equipment, transmission impairment control, and optoelectronic joint optimization, forming an independent and controllable ultra-long span optical communication technology system.
High-altitude communication must first address physical damage caused by low temperatures. In an environment at an altitude of 5,300 meters with winter temperatures as low as minus 60 degrees Celsius, ordinary fiber coatings are prone to embrittlement and cracking, the fiber paste inside the cable gradually solidifies, and the fiber experiences microbending under compression, increasing signal attenuation. The R&D team redesigned the molecular structure of the fiber coating material to create a coating with a low glass transition temperature, maintaining flexibility even at extremely low temperatures. They also developed a high-cone-penetration fiber paste, increasing its cone penetration by more than two times at minus 70 degrees Celsius, reducing the compression on the fiber caused by paste hardening. The resulting low-loss fiber composite overhead ground wire can withstand temperatures as low as minus 70 degrees Celsius and is used in communication lines crossing high altitudes, low temperatures, and geological fault zones.
Submarine optical cables face another set of technical conditions: ultra-high water pressure, long-distance continuous manufacturing, and residual stress within the cable body. Conventional circular steel wire armored structures may deform at depths of 10,000 meters, and relative movement between the optical unit and outer materials can alter the stress state of the fiber.
The project team adopted a self-locking pressure-resistant structure with non-uniform diameter steel wires, layering and tightly stranding wires of different diameters. This allows external water pressure to be primarily borne by the metal armor layer, with over 95% of the pressure isolated from the internal optical unit, enabling the submarine cable to withstand depths of up to 11,000 meters. In the manufacturing process, a multi-dimensional stress sensing and self-feedback speed control system was added. The equipment continuously monitors tension and stress changes during wire laying, stranding, sheath forming, and cable take-up, automatically adjusting production speed and traction parameters to reduce additional losses from long-distance cable formation. This process enables the continuous production of single submarine cables spanning hundreds of kilometers, reducing the number of intermediate joints and the associated risks of reflection, attenuation, and reliability at connection points.
The transmission system also employs impairment suppression and optoelectronic joint optimization methods. The optical layer adjusts signals based on line attenuation, amplifier gain, and channel power variations, while the electrical layer synchronously corrects modulation parameters and reception processing methods, maintaining high-capacity transmission over long-span links in areas lacking relay stations and with limited maintenance conditions.
Currently, this technology has been deployed in operator networks, operating stably in high-altitude cold regions and coastal waters, achieving nearly 1,000 km of broadband optical interconnection. Specifically, related high-altitude lines cover over 1,200 km from Sangri to Mangkang; marine communication lines achieve over 900 km of broadband interconnection between islands. The low-temperature optical cables, deep-sea pressure-resistant submarine cables, optical transmission equipment, and optimization technologies used in the project are all redesigned for extreme environments, rather than directly transplanting ordinary terrestrial optical communication equipment to high altitudes or the seabed.