CHRISTIAN UREMOVIC OPTICAL LINE SYSTEMS
FOR TOMORROW’S NETWORKS REIMAGINING OPTICAL LINE SYSTEMS
Demand for network capacity remains unrelenting, growing at more than 30% per year. Although nascent today, AI traffic will only increase demand. Already, data centre interconnect traffic is the hottest segment of optical networking, with more than 50% annual growth, writes Christian Uremovic , Senior Director of technical solutions marketing at Infinera.
W ith each new generation of returns, service providers are turning their attention to optical line systems and their designs to maximize per-fibre capacity and efficiently support multi-rail deployments. Optical line systems are the foundation of global optical networking connectivity, much like streets and highways are for our vehicles. We need optical line systems to enable connectivity at the edge of the network through metropolitan and core coherent optical engine reaching spectral efficiency limits and diminishing sites, connecting cities, countries, and continents. Increasingly, we need optical connectivity to connect data centres. Optical line systems have long lifespans, often operating for more than 20 years. So, what are the key technologies behind optical line systems, and where do we go from here to keep up with unrelenting capacity demands? In this article, we explore six key technology areas of current and future optical line systems: amplifiers, wavelength-selective switches, dynamic link control, multi-rail parallelism, open networking, and new transmission mediums. AMPLIFIERS – OVERCOMING ATTENUATION AND MORE SPECTRUM Erbium-doped fibre amplifiers (EDFAs) offer solutions for amplifying optical signals or wavelengths, extending
transmission reach, minimizing signal loss, and maximizing network performance. By doping a segment of the fibre with erbium ions, the wavelengths are boosted without being converted to electrical signals. This enables very long-distance transmission of wavelengths, and by cascading amplifiers, we can bridge thousands of kilometres without the need for costly optical-electrical-optical conversion or signal regeneration. EDFAs can amplify only a specific part of a fibre spectrum and, since the late 1990s, have evolved from amplifying 3.2 THz to 4.8 THz of the C-band fibre spectrum. The latest EDFA technology evolution expands their range to 6.1 THz, into the so-called Super C-band spectrum, delivering a 27% boost in fibre capacity while maintaining equal performance. This is similar to increasing the number of lanes on a highway to allow more vehicles to travel simultaneously. Super C-band solutions also lower cost per Hz by about 17% and power per Hz by about 18% in a fully utilized scenario, and they delay or avoid the need to deploy and light up new fibre. Additionally, EDFA technology is available that amplifies the L-band in parallel to the C-band on the same fibre. Recent advancements here have increased the amplification of the L-band fibre spectrum from 4.8 THz to 5.5 THz. Super C+L-band networks help reduce costs and power consumption by potentially eliminating the need for
additional fibres. These solutions are perfect for long-term use, especially where fibre is expensive or scarce, like in international long-haul networks. However, L-band networks add some operational complexity and may not be ideal where sufficient fibre infrastructure exists. Amplifier technology remains an interesting area of innovation. New materials, including thulium, are being investigated to determine the feasibility of amplifying other parts of the fibre spectrum, such as the S-band, O-band, and E-band. The goal remains to further enhance fibre transmission capacity. New amplifier technology is still years away, and further development and economic feasibility studies are needed. WSS – SWITCHING THE LIGHT Another important building block of optical line systems are the wavelength-selective switches (WSSs). WSS technology enables network operators to remotely modify, add, switch, or remove specific wavelengths without affecting other traffic in the network. They are a key part of the so- called ROADM (reconfigurable optical add/drop multiplexer) architecture and provide simple, dynamic, and fully automated operation of wavelengths in optical networks. Technology options for WSSs include micro-electro- mechanical systems (MEMS), liquid crystals (LC), and most commonly, liquid crystal on silicon (LCoS). The wavelengths are typically multiplexed
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| ISSUE 40 | Q1 2025
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