The French/Cajun phrase “laissez les bons temps rouler” used in Louisiana and around the Gulf Coast means “let the good times roll”, and that’s exactly what’s going to happen next week at SubOptic, the triennial submarine network industry event being held in New Orleans, Louisiana. Although not Mardi Gras (Fat Tuesday), SubOptic will celebrate the growth in submarine cable networks, which are considered critical infrastructure , as they carry more than 99% of all intercontinental communications.

There’s also no Plan B for these unseen networks meaning as an industry, we must continue innovating at a frenetic pace to ensure these submerged marvels of network engineering maintain pace with ongoing bandwidth growth exceeding 40% annually on all submerged telecommunications routes of the world, according to TeleGeography.


Submarine Line Terminating Equipment (SLTE) that bookends submarine cables are located on land in a cable landing station, central office, or data center, and houses modems that for years have been the primary focus of technology innovation enabling cable operators to implement step increases in capacity via simple upgrades. For the most part, capacity upgrades are performed via simple swaps of “older” technology with “newer” technology”.

The latest coherent optical modem technology innovation is focused on five key areas, summarized in Figure 1, which yields previously unthinkable total cable capacities when coupled with uncompensated wet plants optimized for coherent optical modem transmission technology. The marriage of coherent modem and wet plant technology, optimized for each other, has yielded channel speed increases over the past decade from 10G to 40G to 100G, and much higher with our GeoMesh Extreme, by leveraging the very latest WaveLogic 5 Extreme modem technology resulting in new milestones in coherent modem performance. The pace of modem innovation continues unabated.

Figure: Five key coherent modem technology areas enabling increased channel and overall cable capacities

Figure 1: Five key coherent modem technology areas enabling increased channel and overall cable capacities

Although the technological wizardry implemented in today’s modems are truly astounding – kudos to the R&D teams – there’s a limit to how many bits we can squeeze into a deployed submarine cable with fixed performance that’s determined when it was initially designed. This roadblock is called Shannon’s Limit, which is the theoretical maximum information transfer rate of a communications channel for a given noise level.

In the case of submarine networks, the “communications channel” is the wet plant’s optical fiber and the “given noise level” comes from the series of concatenated repeaters (submerged optical amplifiers) along the submarine cable route. For over a decade, our industry has continuously moved ever-closer to the Shannon Limit, which was accelerated with the advent of coherent optical modem technology. We’re now knocking on the door of the Shannon Limit with respect to existing wet plant and coherent modem technology, which has resulted in an increased focus on developing new submarine cable (wet plant) designs.


The wet plant hardware technology of an already deployed submarine cable cannot be upgraded in a reasonable or cost-effective manner, as it must be raised from the ocean depths. However, the amount of capacity it transports can be upgraded by upgrading SLTE with the latest modem technology, which has been the case for years. So, if the maximum total capacity of a submarine cable is nearing the Shannon Limit, how do we increase capacities along the world’s submerged information superhighways to maintain pace with voracious bandwidth demands?

Spatial Division Multiplexing (SDM) Submarine Cables

More submarine cables are required, and that’s exactly what’s happening with a slew of new submarine cables being announced, primarily by Internet Content Providers (ICPs). Although more submarine cables will increase the overall capacity, the industry is also looking to improving the total possible capacity of the individual cables themselves.

The performance of recently deployed cables has improved when compared to legacy optical submarine cables by incorporating C+L band support, removing optical chromatic dispersion compensation from the designs, developing lower noise repeater (optical amplifier) designs, and deploying new fiber types. The latest focus of new wet plant designs is Spatial Division Multiplexing (SDM), which are cables with very high Fiber Pair (FP) counts of anywhere from 16 to 32, and even higher in some discussions, which is far more than the common 6 FPs deployed today.

The goal of SDM is to maximize wet plant capacity by balancing a trade-off between available electrical power and the number of FPs using (hopefully) lower-performance, lower-cost modems, albeit many more of them. These designs result in each FP supporting a lower capacity than existing high-performance “lower FP count” wet plants. However, given SDM wet plants have many more FPs, the total wet plant capacity would be higher than existing wet plant designs. Figure 2 below is an example – for illustrative purposes only, as every submarine cable’s performance and allowable capacity is unique – of a future SDM cable capacity compared to a non-SDM cable capacity.

Figure: SDM vs. Non-SDM submarine cable total capacity comparison illustrative example

Figure 2: SDM vs. Non-SDM submarine cable total capacity comparison illustrative example

Although for SDM is indeed promising on paper, there are still numerous questions to be addressed:

  • How many FPs can we electrically power from Power Feed Equipment (PFE)?
  • How many FPs can we reliably splice back together while at sea?
  • Will more “lower-performance” modems be less expensive than fewer “higher-performance” modems?
  • What are the required specifications and cost points of “lower-performance” modems?
  • Given SDM cables operate at power levels, with the saved power shared across more FPs, will SDM cables really have a higher total capacity into the future?

As you can see, there are many questions still to be addressed before SDM cables become a reality, but this is exactly what the SubOptic event is designed to do: explore new ideas, discuss technology options, and decide where the industry should go into the future. We at Ciena have our views on SDM cables and would be happy to discuss the pros and cons of this new wet plant design because once a cable is deployed – it is what it is – for its entire lifespan.

Ciena Presence @ SubOptic 2019

As host of SubOptic event, Ciena is proudly participating in a variety of activities. Besides Gary Smith, President & CEO of Ciena, giving the keynote presentation entitled “Digital Revolution” on Tuesday, April 9 @ 9:30AM, Ciena is also participating in the following event activities.

Monday, April 8

09:30AM: “SubOptic Association Working Group on Open Cables” session

11:00AM: “Open Submarine Networks” masterclass

Tuesday, April 9

09:00: Welcoming Remarks, Ian Clarke, VP Submarine Sales

09:30: “Digital Revolution”, by Gary Smith, Ciena President & CEO

11:00: “High Capacity Optical Link Budgeting for Next Generation Modems” presentation

13:30: “The Business of Submarine Cable Infrastructure, a CEO Debate” panel discussion

15:15: “SDN/SW Control Techniques/Benefits of their Implementation in Submarine Networks” session

16:45: “Maximize the Benefits of Higher Delivered OSNR of Modern Wet Plant” session  

16:45: “Are You Ready for Submarine 400G?” poster session with EXFO

16:45: “Maintenance in a Submarine Network using Analytics” poster session

Wednesday, April 10

14:00: “Google – The Subsea Fiber as a Shannon Channel” session

14:00: “Validating Emerging Transmission Technologies on Submarine Cable Systems” session

14:00: “Virtualizing the Submarine Network – Requirements, Architectures, and Use Cases” session

Thursday, April 11

09:00: “Pre-emphasis-based Equalization Strategy to Maximize Cable Performance” session

10:45 “Support of Higher Baud Rate and Line Rate over a Legacy Submarine Cable System” session

We hope to meet with you and would be happy discussing the very latest technology and business developments in the submarine networking industry, one of the most unique, interesting, and critical parts of the global Internet.

Remember, you’re in the exciting city of Carnival and Mardi Gras, so laissez les bons temps rouler!