47 Tbit/s Capacity per Fiber Pair!

Various strategies can be followed for increasing subsea cable system capacity.  One is to “simply” increase the fiber count (“simply” is placed inside quotation mark as higher fiber count turns into more amplifier pairs to be remotely powered).  Another one is to increase the bit rate of the optical carriers transported along the optical fibers inside the cable (the higher the carrier rate, the shorter the transport distance).  Another option is to increase the optical spectrum of the submerged repeaters so more carriers can be packed together.  Each alternative has its own pros and cons.  And each of them is pursued by the industry in an attempt to respond to the skyrocketing need for higher capacity in backbone networks.

Subsea Cable System Capacity

A few months ago, TE SubCom and Pacific Light Data Communication Co. Ltd. (PLDC) announced that they teamed with Facebook and Google to deploy the Pacific Light Cable Network (PLCN), a 12,800 km transpacific subsea cable system between Hong Kong and Los Angeles.  This ultra-long-haul subsea cable system will be put in service in 2018 with wideband optical repeaters making use of C+L technology.  Instead of being stuck to the C band of Erbium-Doped Fiber Amplifiers (EDFA), the PLCN subsea cable system will feature new repeaters where both C and L optical amplification bands will be available, effectively doubling the fiber capacity.  PLCN will achieve 24 Tbit/s capacity per fiber pair by multiplexing 240 optical carriers at 100G.

Subsea Cable System Capacity

Shorter subsea cable systems allow system designers to use 200G carrier rate.  An illustration of this approach is provided by the Ireland France Cable 1 (IFC-1) subsea cable system.  This 565 km submarine link will come in service in fall 2018 and will be built around C+L repeater and 200G carrier technologies.  This combination will result in the impressive capacity of 47 Tbit/s per fiber pair.  The six fiber pairs of IFC-1 subsea cable system will offer a total capacity of 282 Tbit/s!  To put things in perspective, there were about 337 Tbit/s of potential capacity across the Atlantic Ocean in 2016, based on TeleGeography data.

And the game does not stop here.  With advanced modulation formats, higher symbol speeds and more powerful digital signal processing, the carrier rate is expected to be significantly improved within the next few years, leading to further improvements in subsea cable system capacity!

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