What is space division multiplexing in fiber optic communications?

Introduction to SDM and multicore optical fiber, an emerging area of ​​technological advancement in the communications market.

More data, more capacity – a recurring phrase heard across the fiber communications landscape today. This is certainly the mindset of optical fiber manufacturers, tasked with constantly researching and developing new design methods to meet increasing global demands for bandwidth and data transmission efficiency. Recently, developments in hollow core fiber (HCF) have been widely published, but another emerging technology is space division multiplexing (SDM), which has been achieved using multicore optical fiber (MCF) and few-mode fiber (FMF). This article briefly introduces SDM, focusing on multi-core technology, its known advantages, challenges, applications, and some examples of MCF brands.

Space Division Multiplexing (SDM) – Introduction

Space Division Multiplexing (SDM) is a design concept that aims to increase the amount of data transmitted within an optical fiber, and to expand the capacity within the cables. Unlike traditional single-core fibers with multiplexing techniques that manage multiple signals using wavelengths or time, SDM exploits the spatial dimension of fibers, providing multiple spatial channels within a single fiber. This can be achieved in several ways, including the use of multi-core fiber, which contains multiple cores in a single fiber, and few-mode fiber, which supports transmission across several modes in a single core. Since MCF and FMF differ in their respective approaches (i.e. multiple cores vs. multiple modes in a single core), today we will highlight MCF and address FMF in a future article.

Advantages of SDM and multicore optical fiber

Space division multiplexing technology is designed to transmit larger amounts of data more efficiently, and provides several key benefits:

Greater Transmission Capacity: SDM greatly increases fiber transmission capacity by adding more channels for data transmission, effectively doubling the throughput. In the case of multicore fiber, having two or four cores instead of just one doubles or quadruples the total capacity.
Improved efficiency: By delivering more data within a single fiber through increased capacity, SDM reduces infrastructure costs, as fewer fibers and cables are needed for the network or data center to meet intended data targets or thresholds.
Easier scalability: SDM delivers greater capacity per fiber, delivering scalability improvements by enabling incremental upgrades in data capacity, using fewer cables or potentially reducing the need for additional cables, helping to future-proof against increasing data demands.

Challenges of SDM and multicore fiber technology

Despite the obvious benefits provided by space division multiplexing and multicore fiber, this technology faces some technical and manufacturing challenges that people in the field are actively working to address:

Design and Manufacture Complexity: Multicore and few-mode fibers are more complex to design and manufacture effectively, requiring manufacturers to exercise precise control over core spacing and uniformity to minimize dispersion and modal dispersion characteristics.
Inter-core interference: One of the big challenges in multi-core fiber is inter-core interference, where signal leakage between cores can degrade the quality of data transmission. Therefore, the design and construction of these fibers, in terms of appropriate and consistent core spacing, along with other variables, should minimize interference to improve transmission performance.
Advanced splicing equipment requirements: Since multi-core fibers require precise alignment of all cores when splicing two fibers together, traditional single-core fiber splicing machines are insufficient. Therefore, more advanced coupling devices that include rotational alignment capabilities are needed. As expected, these devices usually require a much higher investment due to their advanced capabilities.
Cable Breakout, Breakout, and Termination Design Decisions: For those who manufacture multicore fiber and/or deliver it in a cabled format for network deployment, questions arise about different approaches to breaking up individual cores and their transmissions from a cabling perspective. What is the best and most efficient way (from a manufacturer and user perspective) to move from multi-core single fiber to single core single fiber cables? What types of fans will be used, if any, or will a direct connection device approach (similar to active optical cables) between equipment be preferred? The list goes on, but there should be more clarity on the near horizon to address these challenges.

SDM and multicore fiber communications applications

Space division multiplexing and multi-core fiber technology appear to represent a viable solution for any network operators and service providers seeking to extend their bandwidth and transmission capabilities more efficiently. Some examples are:

Data Centers (Inter and Intra)
Telecom backbone networks/Internet service providers
Submarine and transoceanic networks

Manufacturers and brands of multicore optical fiber

Many globally recognized entities in the optical fiber communications market are at the forefront of design, development and manufacturing of multicore optical fibers.


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It should be noted that this is only a partial list of entities that manufacture multicore optical fibers, as there are other large and small entities developing multicore, low-mode, and other optical fibers within the SDM field for communications applications.

SDM and MCF – shaping the future of optical communications

SDM and multicore fiber, although still early in the development and deployment life cycle, represent a promising future in terms of fiber communications innovation. Similar to advances in any new technology, SDM and multicore fiber (along with few-mode fiber and other fibers in this category) have realized benefits and technical hurdles that must be overcome if the ultimate goal is mass production and deployment across global networks. At this time, it appears to be already gaining acceptance and heading in a positive direction, ultimately positioning the technology to play an integral role in fiber networks now and in the near future.

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