There is a relatively new fiber technology that most readers will not have heard about. Multi-core fiber (MCF) is a technology that packs multiple strands of fiber inside a bundle that is about the same size as a single strand of fiber today. The benefit of packing more fibers into a tiny strand is obvious – it means a lot more bandwidth can be sent through a single physical strand of fiber.

It may surprise you to understand that only a small fraction of a strand of fiber is used to transmit light. In today’s fiber, the light path in the center of a fiber is tiny and represents only 0.5% of area of a cross-section of a fiber. The rest of the fiber strand is made up of materials surrounding the glass that help to keep the light on a straight path and cladding that protects the fiber. Fiber could be made a lot thinner, but the industry has standardized on a fiber strand of 125 microns because going any smaller makes it hard for technicians to handle a single fiber strand. This means there is a lot of unused real estate inside a 125-micron sheath for additional light paths.

Early prototypes of multi-core fiber have created fibers with 7, 12, and 19 fibers, with the possibility of getting even more cores into a single strand. Each core is equivalent to a single-strand of fiber today. A 24-strand cable that uses 12-core multi-core fiber would contain 288 separate fiber paths. Future networks using multi-core fibers will be lighter and easier to handle than the fibers they would replace using current technologies.

There are some obvious issues with using multi-core fibers. One is cost, and MCF fiber is a lot more expensive today than traditional fiber. But that difference might be eliminated if MCF fiber becomes common and is produced in volume. The extra cost of the fiber might be easily offset by the increased ease of working with smaller fiber bundles. There are major challenges of splicing an MCF fiber into an existing network comprised of single-strand fiber. MCF fiber also interfaces in a whole new way with fiber electronics. There is also a size issue, because MCF fibers with a lot of cores will be larger than 125 microns, meaning that all new tools are needed to work with the fiber.

There are already a few trials of MCF fiber in use. This is a natural improvement for undersea fibers, where getting the most bandwidth possible in a fiber bundle is desired. There is also MCF fiber installed in some data centers to facilitate moving huge amounts of data from device to device.

Multiple vendors are manufacturing or testing multi-core fiber and it will become more available over time. This seems like a natural upgrade to long-haul fiber routes between major cities. There has been a lot of industry concern that the explosion of data centers means these long-haul routes are filling up soon after being constructed. MCF fiber multiplies the bandwidth that can be delivered through existing conduits.

One of the concerns of having many tightly packed cores side-by-side is crosstalk and interference between cores. However, scientists seem to have solved this problem with good shielding materials around each core.

It may be a long time before this makes sense in last-mile networks. We can already deliver far more bandwidth than almost any customer needs with current fiber technology. However, MCF answers the question of whether fiber technology will ever be obsolete. No wireless technology will ever be able to outcompete a small MCF fiber strand with multiple cores in each small fiber strand.