Submarine SDM Cable – Efficient way to Increase Subsea Capacity

Introduction

 There are different ways to meet the high traffic demand in Submarine cable. We need more capacity. Demands keeps on increasing. How we can achieve it?

More Submarine cables, more number of channels (C+L band system), more number of fiber pairs, increasing per fiber capacity, increasing channel bandwidth i.e transponder/modem capacity.

Before 2018, the focus was on increasing the per fiber pair capacity. However, it has almost reached the maximum. Then why not, increasing the capacity in system level.

Increasing the capacity of submarine cable by adding more fiber pairs is called SDM.

 In the past, everyone’s goal was to maximize the amount of bandwidth per fiber pair, more wavelengths, and a higher bit rate per wavelength. Now the trend has been shifted to an emphasis on more fiber pairs in a single cable. These new cables being planned with so-called SDM. 

Traditional cable has 4 to 8 fiber pairs. The maximum what we know in traditional subsea cable is 8 fiber pairs. While SDM cable will have 12 to 16 fiber pairs and potentially more in future. More fiber pairs, more cable capacity.

 Recently, we have heard announcements of SDM cable. Greater capacity can be realized through spatial division Multiplexing (SDM) in which more fiber pairs carry channels with lower power and signal-to noise ratio (SNR). 

Traditional Submarine vs SDM Submarine Example

Traditional Cable Example: 6 fibre pairs * 20Tbps each = 120Tbps Total Capacity

SDM Submarine Cable Example: 16 Fibre pairs * 16Tbps each = 256Tbps total capacity

As per the sources, first SDM submarine cable will be Google’s transatlantic 6,400km Dunant cable, which supports up to 250Tb/s of overall capacity provided by an aggregate of 12 fiber pairs.

The recent announcement of SDM submarine cable is 2Africa, 37,000km long, with design capacity upto 180Tb/s on key parts of system with 16 fiber pairs.

We expect more and more new Submarine SDM cable announcements in coming years. Next 10 years, it will be era Submarine SDM Cables.

Single Mode or Multi Core Fiber in SDM ?    

Currently, it is single mode fibers & no multi core fibers used in Submarine SDM. May be in future multicore fibers may be used.  

SDM cable vs Traditional Cable comparison 

Conclusion

SDM is the efficient way to increase the capacity of Submarine Cable in system level. SDM is revolutionizing Submarine industry by using more fibre pairs, Low power, Low OSNR and Low Effective Area Fibres ( Aeff ). Currently, we are speaking about 200Tb/s -300Tb/s Submarine SDM Cable. Can we see 1Pb/s or more in future? 

About the Author

Abdul Ravoof, Senior Engineer - Submarine, Transmission Network & Data Center at Integrated Telecom Company (ITC) in Saudi Arabia