Emerging Trends in Optical Fiber: Hollow-core and Multicore Fibers

Posted by Kevin Miller on Wed, Jun 12, 2024 @ 14:06 PM

Hollow-core and Multicore Optical Fiber Diagram - M2 OpticsServing as the backbone for many of today’s essential high-speed communications applications, optical fiber has been one of the most important technological advancements of the modern world. From supporting internet connectivity for people and businesses to connecting industrial automation systems, optical fiber enables the transmission of vast amounts of data for services we rely on daily.

Since its inception decades ago, optical fibers have typically been designed and manufactured using an approach that involves a thin strand of glass comprised of a single, solid glass core in which the light signals propagate, encapsulated by a glass cladding layer with a different refractive index that helps keep the light within the core during transmission. Along the way, optical fiber has incurred many iterations of positive advancements, resulting in the fibers we have today that efficiently deliver data at unprecedented levels in a low-loss, low-latency manner.

However, as data demands continue to soar currently in 2024 and are expected to continue this upward trajectory for the foreseeable future, leading fiber manufacturers have been working on several new designs intended to increase capacity, reduce latency, or both. The two types that appear to be showing the most promise for optical fibers in terms of viability are Hollow-Core Optical Fiber (HCF) and Multicore Optical Fiber (MCF), so far demonstrating some real improvements in speed, bandwidth, and capacity.

Let’s take a brief look at both types of fiber, including their technical composition and primary performance benefits, along with a few examples of the fiber brands and companies at the forefront of these innovation efforts.

Hollow-Core Optical Fiber (HCF)

Hollow Core Optical Fiber, as its name implies, is a type of optical fiber in which the core is hollow and comprised of air rather than solid glass. This unique structural design approach significantly alters the fiber's light propagation properties, enabling several performance advantages over conventional fibers with solid glass cores.

HCF Benefits and Applications

There are a few technical advantages that can be realized by utilizing an optical fiber that enables transmitted light signals to travel through air instead of glass.

  • Reduced Latency: The speed of light is determined by the Index of Refraction (IOR) of the medium through which light travels – the higher the IOR value, the slower it travels. Air has a significantly lower IOR value than glass, so HCF allows light to travel faster through its core, significantly reducing latency by 30% or greater, as reported in a whitepaper by the HCF manufacturer OFS®. These latency improvements are crucial for applications requiring real-time data processing, such as high-speed financial trading and autonomous vehicles, which have already implemented some of the early-stage developed hollow-core fibers into their networks.

  • Improved Bandwidth / Larger Spectrum: The air core of an HCF can support a broader range of wavelengths, therefore increasing potential bandwidth capabilities. Having additional spectrum available to use is beneficial for high-capacity data transmission and future-proofing telecommunication infrastructure.

  • Low Attenuation: While the earliest versions of HCF demonstrated significantly higher attenuation (signal loss) than current traditional glass core optical fibers, recent improvements by some manufacturers have resulted in demonstrations showing that HCF can achieve similar reduced attenuation values required for optimal performance. Often deployed over short distances within data centers to this point, HCFs expected forward progress of consistently achieving reduced attenuation values could make this fiber suitable for mass deployment in the longer-distance metro, regional, or even submarine/transoceanic transmission applications.

Companies Leading Hollow Core Fiber Innovation

While still in the early stages of the technology lifecycle, a few well-known companies have been at the forefront of developing high-performance hollow-core optical fibers for network and data center applications.

Note: These major entities are not the only companies that manufacture hollow-core fibers, as there are several other entities (ex: ThorLabs, NKT Photonics, etc) that offer HCF for specialized communications.

Multicore Optical Fiber (MCF)

Based on the design concept of Space Division Multiplexing (SDM), Multicore Optical Fiber is a type of fiber that consists of multiple cores within a single strand of fiber. Each core operates independently, allowing multiple data streams to be transmitted simultaneously through the single fiber. This physical multiplexing capability using multiple cores significantly enhances the data capacity of each fiber, as a 2-core MCF essentially delivers twice the amount of data as a single-core fiber, and so on.

MCF Benefits and Applications

  • Higher Data Capacity: By allowing for multiple, independent light streams to be transmitted in a single fiber simultaneously, MCF offers a viable solution for vastly increasing the data capacity of a network. Additionally, utilizing wavelength-division multiplexing technology (WDM), which allows for multiple channels of data to be transmitted together in the same signal within a core, exponentially increases the amount of data that can be transferred using a single MCF.

  • Increased Physical Capacity and Space Savings: By offering multiple cores within a single fiber, MCF reduces the need for utilizing multiple independent single-core fibers, thus reducing the total quantity of fibers and cables, saving space in fiber conduits and routes, along with reducing the complexity of fiber management in dense data center environments. As a basic example, using a single patch cable with a 4-core MCF to replace four individual single-core fiber patch cables yields 75% physical space savings.

  • Enhanced Network Efficiency: With the combined benefits of more data capacity and space savings together, MCF helps to simplify and enable more efficient network architectures, capable of meeting growing data demands with practical scalability in mind.

Companies Leading Multicore Fiber Innovation

Like HCF fibers, multicore fibers are still in the development infancy period, but there are several examples of prominent companies aiming to make a splash which include:

Note: Other companies in this arena that also offer multicore fiber include Fibercore and iXblue, as just a few additional examples.

The Future of HCF and MCF – A Look Ahead

While it is unlikely that traditional single-core optical fibers will go away any time soon, both hollow-core and multicore optical fibers appear to represent the exciting next generation of optical fiber innovation, especially for meeting the demands of faster, more efficient, and higher-capacity networks. With key players in the industry like Sumitomo®, OFS®, and Microsoft® making significant investments into further developing these specialty fibers and already noting real deployments in the data center and financial trading arenas, that future is already here.

It will be interesting to see the direction of HCF and MCF design and production over time, as many questions still currently remain in terms of their outlook. What will the global demand picture look like for both types of fiber in the long run? Will they ultimately replace traditional single-core fibers to a major degree across entire networks or will their use be limited to more specific areas or applications? Will service providers prioritize latency advantages and skew more towards HCF or capacity increases and skew more towards MCF?

On the manufacturing side of things, the competitive landscape is always changing. Which ones will be able to successfully leverage their resources and expertise to achieve performance advantages along with mass-producing the fiber reliably and cost-effectively? What technical and manufacturing hurdles will they need to overcome? Will Microsoft® eventually make its HCF available to the larger market or keep its use internal and/or for select business cases? Will OFS® and Sumitomo® establish themselves as market leaders for their respective fibers due to their early-mover progress?

It should also be noted that the name of one key player, arguably the largest and most influential company to pioneer and produce optical fiber, has not yet been mentioned - Corning®. As of the date of this article, Corning® has yet to make any public announcements in terms of HCF or MCF development or production efforts. However, always at the scientific forefront of new fibers with an eye on the future, it will be interesting to see if, when, and how they make an impact with these fiber types or if they pioneer an alternative approach entirely.

One thing is certain – the future is bright for the development of new optical fibers for high-bandwidth, low-latency networks. At this juncture, the same can be said for both hollow-core and multicore technology, which are demonstrating performance benefits that align with future data delivery needs and expectations.

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If you would like to learn more about hollow-core and multicore fibers, or you require custom lengths of these fibers for network and latency simulation testing or optical time delay applications, contact M2 Optics at your convenience.

Topics: optical fiber, hollow-core optical fiber, fiber optic networks, multicore optical fiber