On October 19, the 2026 Global Fiber Optic Cable Conference opened. At the conference, the Technical Requirements for Weakly Coupled Single-Mode Multi-Core Fibers for Communication - Part 1: Cutoff Wavelength Displaced Weakly Coupled Single-Mode Multi-Core Fibers, jointly compiled by Fenghuo Tongxin, Hengtong Guangdian, Zhongtian Keji, Yongding, Yuandong Tongxun, Shanghai Daxue, and other units under the leadership of the Technical Committee of the Asia-Pacific Fiber Optic Cable Industry Association (APC), was officially released.
This standard comprehensively specifies the geometric, optical, mechanical, and environmental performance indicators for weakly coupled single-mode multi-core fibers. It is compatible with the 125μm standard cladding and includes 2-core and 4-core specifications. The crosstalk between cores is extremely low, allowing them to be used like independent single-core fibers. Previously, ITU-T G.Suppl.87 was only a guiding framework document for the standardization of multi-core fibers, not a complete product specification that could be directly used for product inspection.
Ao Li, Deputy Dean of Zhongguo Xintongyuan, mentioned at the conference that foreign institutions are also advancing their respective standards, and similar international standards are expected to be released in 2028.
In the past two years, multi-core fibers have attracted attention, fundamentally because the capacity expansion space for single-core fibers is narrowing.
Creating multiple independent cores within the same fiber cladding is equivalent to 'packaging several traditional single-mode fibers into a single glass fiber as thin as a hair'. This is Space Division Multiplexing (SDM) technology, where a single fiber can transmit multiple optical signals in parallel, significantly increasing the total bandwidth of a single fiber.
To increase the capacity of single-core fibers, methods such as improving single-channel rates, broadening bands, and superimposing wavelength division multiplexing are relied upon, but this path is already approaching physical limits.
Multi-core fibers turn to space to increase capacity. Among them, the weakly coupled route has low inter-core crosstalk, allowing each core to transmit and receive independently and reuse existing single-mode devices. The engineering retrofit cost is lower than that of the strongly coupled route, which requires complex MIMO algorithms, making it more likely to be implemented first. AI computing centers have high internal wiring density, and submarine cables are constrained by pipeline routing and weight, making them two scenarios most sensitive to capacity per unit cross-section.
Previously, multi-core fibers only had specifications from individual enterprises and laboratories, lacking unified definitions for the number of cores, core spacing, cutoff wavelength, and crosstalk indicators. Downstream submarine cable projects and AI computing centers could not bid and accept according to the same standard. This time, fixing the weakly coupled category and the configuration with cladding dimensions compatible with the existing network is equivalent to providing a common reference for product design, production inspection, construction, and operation and maintenance.
In terms of industrialization, Fenghuo Tongxin has been conducting research on multi-core multiplexing technology since 2013. In 2019, it achieved a transmission rate of 1.06Pbit/s with its self-developed 19-core fiber. Currently, it has the manufacturing capability for 4-core, 7-core, 19-core, and 24-core fibers, with the transmission capacity of the 24-core fiber reaching 5.29Pbit/s. The 7-core multi-core fiber submarine cable system it built between Guishan Island and Wailingding Island in Zhuhai has been commercialized. In September this year, a consortium formed by Fenghuo and the Design Institute of Zhongguo Yidong Group won the bid for the general contracting project of the multi-core fiber submarine cable on Gulangyu Island, Xiamen.
However, the demand scale for multi-core fibers is still in its early stages. Ao Li estimates that by 2030, the demand for multi-core fibers will exceed 2.7 million core-kilometers, while the total global demand for fiber optic cables in 2026 is about 630 million core-kilometers. The two statistical scopes are different and cannot be directly subtracted, but in terms of order of magnitude, multi-core fibers are still in the transition stage from demonstration to large-scale commercial use. The specific customer structure and shipment pace remain to be disclosed later.