Making Open Submarine Cables Work: The Need for Intelligent Optical Power Management

Geoff Bennett
Director of Solutions & Technology, Infinera

By Geoff Bennett, Infinera
September 18, 2023

There are over 550 submarine cables under the seas and oceans of the planet – 480 in operation and a further 70 under construction. Over 99% of intercontinental traffic passes over these cables, carrying updates from our Facebook friends, Google searches, and over $10 trillion in financial transactions every day. These cables are typically designed with a 25-year engineering life, but their potential capacity has increased by a factor of 12 or more thanks to the evolution of coherent transponder technologies.

Mid-life upgrades are vital for maintaining the economic effectiveness of the cable. However, the question arises: who provides those updated transponders? Over the past 25 years, submarine cable technology has evolved, with different generations focusing on different types of transponder and capacity growth strategies.

In the early days, submarine cable projects were usually turnkey projects carried out by a single company. Today, open submarine cables are more common, where the wet plant and submarine line terminal equipment (SLTE) can be purchased from different vendors. This flexibility allows for the use of best-of-breed transponders throughout the cable's engineering life.

This article aims to answer key questions about the transition from turnkey to open cables, the benefits and potential drawbacks of open cables, the need for optical power management, and how to maximize the benefits of open cables while minimizing the drawbacks.

From Turnkey to Open

In 2007, submarine cables were typically turnkey projects designed to support 10 Gb/s transponders. The most significant optical impairment at that time was chromatic dispersion, which was compensated for in the cable itself. As contractual restrictions for some of these turnkey cables began to expire, cable operators started using cheaper and readily available terrestrial transponders.

The advent of coherent transmission around 2009 revolutionized the market, allowing for higher data rates and fiber capacity over existing fibers. By 2010, the first generations of 40G and 100G coherent transponders were being deployed on existing dispersion-managed cables, leading to a significant increase in capacity per fiber pair.

The Advantages of Open Cables

Open cables offer flexibility, allowing fiber pair operators to deploy the best-of-breed coherent transponders over the cable's lifetime. Each generation of transponder brings advantages such as higher spectral efficiency, smaller footprint per Gb/s, and lower cost and power per Gb/s of service traffic. Open cables are usually offered on a per-fiber-pair basis, but there is a trend towards dividing the spectrum within a fiber pair and offering chunks of spectrum to different tenants.

The Challenges of Open Cables

Open submarine cables face challenges similar to those in terrestrial open optical networks. Performance standards need to be defined, and automating the process of open cable characterization is essential. Optical power management is also a challenge in open cables, raising the question of who is responsible for managing it.

The Need for Optical Power Management

Optical power management is crucial in all submarine cables. Long-distance submarine cables use in-line optical repeaters, which operate in constant power mode. Maintaining the optimum power level is essential to prevent service wavelengths from experiencing too much amplification or falling below their minimum OSNR level. In turnkey cables, the wet plant vendor would provide a solution for power management. In open cables, fiber pair operators are free to choose a best-of-breed optical power management solution.

To read the complete article, check out Issue 132 of the SubTel Forum Magazine here