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In Milan, Open Fiber has activated Italy’s first real-world telecommunications link based on multicore optical fiber, a technology designed to expand network capacity without laying additional cables or opening new construction sites.
The connection links two network points of presence, known as PoPs, in the Baggio and Galvani districts through a route of about 2.1 kilometers that is already carrying telecommunications traffic. The novelty lies in the structure of the fiber itself. Traditional optical fibers carry data through a single optical core. Multicore fiber contains several independent cores inside the same strand. In the Milan deployment, there are four.
The approach allows network operators to increase transmission capacity while using the same physical infrastructure. In practical terms, a single fiber can carry traffic volumes that would otherwise require multiple separate links. The advantages are particularly significant in the upper layers of the network, including connections between switching centers, PoPs and data centers, where large amounts of internet traffic are concentrated.
According to the company, the technology could reduce the total number of cables needed and limit new construction work, requiring fewer installations and fewer network devices to manage data traffic. That could also reduce energy consumption, especially in data centers, where power and cooling systems account for a substantial share of operating costs.
Until now, multicore fiber had remained largely confined to research laboratories and experimental projects. The Milan connection is one of the first operational deployments on a commercial network in Italy.
Why the Telecommunications Industry Is Looking for Alternatives
Research into multicore fiber is driven by a problem the telecommunications industry has debated for years: conventional optical fibers are gradually approaching their physical and energy limits.
Modern networks rely primarily on single-mode optical fibers, which transmit light signals through a single optical core. Over the past decades, the capacity of these fibers has steadily increased through more sophisticated modulation systems and by transmitting multiple channels simultaneously over the same fiber. But that growth is becoming increasingly difficult to sustain.
As transmission volumes rise, light signals begin interfering with one another. Beyond a certain threshold, increasing signal power or adding more channels produces more noise, more transmission errors and greater energy consumption. Researchers often describe this as one of the major physical constraints of modern optical communications.
The challenge is not limited to the fiber itself. Managing enormous quantities of data also requires increasingly complex electronic systems with high power demands and substantial cooling requirements. The rapid expansion of data centers and artificial intelligence applications has intensified those pressures.
For that reason, telecommunications companies and research institutes have increasingly turned toward technologies based on what is known as “space division multiplexing,” which distributes traffic across multiple physical channels instead of concentrating it within a single optical core.
How Multicore Fiber Works
Multicore fiber follows that principle directly. Instead of continuously increasing the amount of data carried through a single core, it distributes traffic across multiple independent cores contained within the same physical cladding.
The goal is to increase network density: more transmission capacity within the same physical space occupied by existing cables. That could reduce the number of fibers required, simplify cabling systems and decrease the number of devices needed to manage traffic flows.
In recent years, experimental systems have reached transmission speeds measured in petabits per second, or millions of gigabits per second. Research has focused particularly on internet backbone infrastructure and data center interconnections, where traffic volumes continue to grow rapidly because of cloud computing, video streaming and artificial intelligence services.
One of the most significant technical problems is known as “crosstalk,” interference between the different optical cores inside the same fiber. When signals interfere with one another, transmission quality deteriorates and error rates increase. Much of the current research is aimed at reducing those interferences through new core geometries, different materials and more advanced signal management systems.
Manufacturing also remains more complex than with conventional fiber. Multicore systems require highly precise connectors, switching equipment and splicing techniques because several optical cores must be aligned accurately inside the same strand while maintaining stable transmission across all channels.
From Research Labs to Operational Networks
Research on multicore fiber dates back to the 1970s, but accelerated after 2008, when the telecommunications industry began seriously considering the possibility that traditional optical fibers could eventually reach practical capacity limits. Since then, the number of cores integrated into experimental fibers has steadily increased, moving from early four-core and seven-core systems to fibers containing dozens of independent channels.
Researchers have also developed new devices compatible with multicore networks, including optical switches capable of routing signals between different fiber cores at extremely high speeds. Some laboratory prototypes can redirect signals in less than a microsecond while maintaining performance compatible with high-capacity telecommunications systems.
Despite those advances, multicore fiber is not yet widely deployed. Costs remain high, and industry standards are still evolving, making interoperability between manufacturers and network operators more difficult.
For that reason, the Milan project is less a final breakthrough than an early attempt to move a technology studied for decades out of laboratories and into operational telecommunications networks.