Submarine Networks – Today and Tomorrow

Submarine Networks –Today and TomorrowGeoff Bennett

Director, Solutions and Technology

Geoff BennettDirector, Solutions & TechnologyNottingham, United Kingdom

Today’s Rules

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Poll Question

From Telegraph to Telephone to Data

Telegraph → Telephone

TAT-1 TAT-2 TAT-3 TAT-4 TAT-5 TAT-6 TAT-7

36 48 138 138

Transatlantic Cable Capacity (circuits)

1956 1959 1963 1965 1970 1976 1978

Telstar 1July 10th 1962

Intelsat 1April 6th 1965

Before 1956 calls were made over radio telephony

Copper vs Fiber Capacity Levels

TAT-1 TAT-2 TAT-3 TAT-4 TAT-5 TAT-6 TAT-7 TAT-8

36 48 138 138 845 4k 4k

40kCopper

Transatlantic Cable Capacity (circuits)

1956 1959 1963 1965 1970 1976 1978 1988

Transatlantic Fiber Optic Cable Evolution

From TAT-10 onwards cable capacity moves to data rate, not telephone channels…

…because, by 1992, voice was just another type of data

Source: Wikipedia

Today there are a lot of submarine cables!

Europe

Mediterranean

They carry >95% of

international bandwidth

telegeography.com

How much traffic is carried by Submarine Cables?

Growth is forecast at 39% CAGR from 2019-2026

ICPs dominate globally

Worldwide Growth

Source: Telegeography 2020

Historically transatlantic and trans-pacific, but spreading to all routes

About 1.5 x 1015 bits per second(1.5 petabits per second)

Are we in another bubble?

Not even close…

Dotcom Bubble

Post Bubble

Coherent

SLTE Upgrades ICP SurgeCap

The anatomy of a submarine cable

Laying the cable

Cable laying ship

PloughCable

Submarine cable

Amplifiers in Submarine Cables

+10kV -10kV

50-80km

25 year design life

Danger to Submarine Cables

Sharks!

• Sharks did used to attack galvanictelegraph cables

• 1988 onwards – metal tape screening introduced

• No more problems with sharks!

On average there are over 100 cable outages per year – but you rarely hear about them

Circa 2009Before 2010

Open Cables: Key Trend in Submarine Cables

Cable vendor gets 100% transponder revenue

Closed Cables

Closed cable contracts expire

UpgradesCoherent!

2014→

New cables are designed to be “Open”

Vendor A

Wet Plant +Vendor A

Vendor B...

Vendor Z

Transp

Accelerated Innovation

Spectrum Sharing

• One network operator for the cable

– Possibly different operators per fiber pair

– Possibly different operators on a single fiber pair

• Challenges

– How to “accept” the new cable is RFS?

– How to manage spectrum for multiple tenants

Open Cable Network Architecture

BackhaulTo the Wet Plant

Power Management Controller

ASE and/or Idlers

Vendor A Transponder(s)

Vendor B Transponder(s)

Infinera Transponder(s)

Cable Landing Station

PoP orData Center

“Glass through”

Some or all transponders will be located in PoP/DC

Wet plant monitoring

Submarine CableCapacity Evolution

Poll Question

Submarine Cable Types

+ve -ve +ve -ve +ve

Dispersion Managed Cable (→2010)

Deployed up to 2010

Examples: Hundreds of cable systems worldwide

Uncompensated (2014→)

Deployed 2014-2019

Positive Dispersion

Examples: SeaBRAS-1, MONET, BRUSA, MAREA, AAE-1 etc.

Festoon/Unrepeatered3

No Amp Chain

Examples: Dozens of cable systems worldwide

Space Division Multiplexing (2020→)

RFS 2020 onwards

Examples: Dunant – others in planning

Ultra Long Haul

Relatively Short Distance

Dispersion Managed Cables

+ve -ve +ve -ve +ve

Dispersion Managed Cable (→2010)

Deployed up to 2010

Examples: Hundreds of cable systems worldwide

These cables were designed and deployed before coherent

technology was available

Chromatic dispersion has to be managed by alternating positive

and negative dispersion fibers along the cable

Capacity Evolution over Dispersion Managed Cables

• Example: Transatlantic cable – Dispersion Managed – Transponder Evolution

– Four fiber pairs

– Design capacity: 800 Gb/s per fiber pair (80 waves at 10Gb/s per wave)

2005 2010 2012 2016 2020

3.2Tb/s

10GIM-DD 12.8Tb/s

40GCoherent

32Tb/s

100GCoherent 40Tb/s

200GCoherent 48Tb/s

LC-PCSCoherent

MAREA: A Coherent-Optimized Submarine Cable

The Field Trial ResultsThe Cable System

MAREA Cable System

Virginia Beach, USA to Bilbao, Spain

6,644km

Large Area, +ve dispersion cable

Production Gear – Hero Capacity6,644 km One-Way Results (16QAM)6.21 bit/s/Hz Spectral Efficiency26.2 terabit/s capacity

13,210 km Loopback Results (8QAM)4.46 bit/s/Hz Spectral Efficiency18.6 terabit/s capacity

Commercial Margin Capacity

24.2 Tb/s

6,644 km

Virginia Beach

Bilbao

Where Next for Increasing Cable Capacity?

Submarine Amplifiers and Capacity

←C-Band EDFA→

Amplifier Location

• Submarine cables need amplifiers

• Amplifiers must be powered

Amplifier power is inserted at cable end points

+10-15 kV -10-15 kV

Amplifiers are only about 1.2% efficient

Copper conductor has resistance of about 0.75 Ω/km

Transponder performance depends on high OSNR – so high amp power levels

Let’s look at some key facts

Technology Option: Light C+L Bands

←C-Band EDFA→←C-Band EDFA→

←C-Band EDFA→

XTb/s capacity at the cost of 4 fiber pairs

Amplifier Location

←C-Band EDFA→

←C-Band EDFA→←L-Band EDFA→

←L-Band EDFA→ XTb/s capacity at the cost of 2 fiber pairs

Amplifier Location

C+L doubles fiber pair capacity, but has

no effect on total cable capacity

Limited by ability to power the amp chain

C Band only

C+L Band

What is SDM? → How do we maximize capacity?

←C-Band EDFA→

Amplifier Location

Cable design goalsMaximize capacity

per fiber pairMaximize capacity

per cable

• Shorter amp spacing

• Higher amp power

• Higher order modulation

• Fewer fiber pairs

• Examples:

• MAREA, BRUSA, etc.

• Longer amp spacing

• Lower amp power

• Pump sharing

• LC-PCS

• More fiber pairs

• Example: Dunant

All of these work to limit the number of fiber pairs in the cable

SDM Comparison: MAREA vs Dunant

• 6,600 km cable

• 8 fiber pairs

• 24 Tb/s per fiber pair*

• Total capacity 192 Tb/s

• 6,600 km cable

• 12 fiber pairs

• 25 Tb/s per fiber pair**

• Total capacity 300 Tb/s*In service **Planned

MAREA Dunant

SDM RoadmapFuture transatlantic cable

40 fiber pairs @ 25Tb/sPetabit scale cable

State of the art UNCOMPENSATED cable

State of the art SDM cable

Challenges for Submarine Transponder Design

Poll Question

Cable and Transponder Life Cycles

Submarine cable design lifetime

25 Years

Coherent optical engine technology cycle

4 Years

The cable you lay this year may not be the “ideal cable” for future transponders

Regardless of cable type, each generation of transponder delivers more capacityBUT…

The only real solution…

You need a comprehensive toolkit

ICE6: 5th Generation Coherent Optical Engine

PIC7nm DSP Analog ASIC

• Compact DCO

• 1.6Tb/s Optical Engine

• 2λ x up to 800Gb/s

XTCDRX

Groove (GX)

Ultra High Baud Rate

(32-96 Gbaud)

20% 33%

High Gain SD-FECSubsea Modulations

(ME-8QAM, etc)

LC-PCS

Gain Sharing

SD-FEC Gain SharingShared Wavelocker Lightning Tolerance

1529 1567 1569 1610

C+L Band

Nyquist Subcarriers DBA Super-Gaussian Encryption

TERMINOLOGY: Nyquist Subcarriers: What and Why?

Carrier 1 Carrier 2

Subcarriers Subcarriers

Carrier 1 Carrier 2

1st Gen: No shaping 2nd Gen: Nyquist shaping

• Higher spectral efficiency

• Driven by FlexGrid

ICE4: Nyquist subcarriers

• Higher spectral efficiency

• Enhanced clock recovery

• Linear tolerance

• Non-linear tolerance

ICE6: Nyquist subcarriers

• Add subcarriers

• High Baud rate carrier

• Low Baud rate subcarriers

Carrier 1 Carrier 2

Subcarriers Subcarriers

Two options for increasing capacity*

*For both per-wavelength and total fiber capacity

4 Bits/symbol2 Bits/symbol

QPSK 16QAM

Increase the modulation order

(ie. bits per symbol)

TimeTime

Symbols per Second

Increase the Baud rate

(ie. symbols per second)

Baud Rate Dependencies: Chromatic Dispersion

Baud Rate

nChromatic Dispersion is a function of Square of the Baud Rate

(2xBaud Rate = 4xCD)

CD can be a big problem for trans-oceanic (14,000km+)

Coherent Transceiver

CD Compensation NOISE

Compensating CD creates noise inside

the transceiver (lower modem SNR)

Uncompensated cables rely on high CD to mitigate nonlinear effects

Baud Rate (Gbaud)

4 8 16 33 66

FWM SPM

Single carrier32 Gbaud → 66 Gbaud

Most DWDM vendors

Nyquist Sub-carrierOptimized PerformanceWhile maintaining economic

advantage of higher Baud rate

200Gb/s @ 16QAM4 x 8 GBaud

800Gb/s @ 64QAM8 x 12 GBaud

Baud Rate Dependency: Nonlinear Effects

Higher Order Modulation

PM-QPSK PM-8QAM PM-16QAM PM-32QAM PM-64QAM

Spectral EfficiencyX1 X3

X1X30 Optical Reach

Why do we lose so much reach at higher orders?

PM-64QAM

PM-QPSK

PM-QPSK PM-64QAM

Let’s draw the symbols that a receiver would see

Maybe we could increase the distance between constellation points…

The closest other symbols for QPSK are a

long way away

The closest other symbols for 64QAM are really close!

But the further from the constellation origin, the higher

the power of the symbol –which triggers non-linear effects

Optical Reach

The challenge with “hard” modulations

Shannon Limit

Imagine if we could “smooth out” the sawtooth

QPSKImagine if we could “move the curve” closer to the Shannon Limit

These are two aspects of Probabilistic Constellation Shaping

Probabilistic Constellation Shaping (PCS)

Start with a 64QAM

constellation

We know the outer symbols are a

problemMore bits per symbol,

shorter reach

Fewer bits per symbol, longer reach

So we use a clever Distribution Matcher to

manipulate the probabilities of using certain symbols

Remember the “sawtooth” curve?Fi

Optical Reach

Shannon Limit

By adjusting the probability distribution we can smooth out the sawtooth edges

More bits per symbol, shorter reach

Fewer bits per symbol, longer reach

The capacity-reach performance is moved closer to the Shannon Limit

100 100 100 100 100 100 100 10085 90 110 115 115 110 90 85DBA →

ICE6 : 800Gb/s waves, 8x12GBd subcarriers

Goal: Team to carry 800 lbsas far as they can in 1 hour

Option 1: 100 lbs per person

Weaker members slow the team down

Option 2: The strongest members carry a little more than the weaker members

Result: The whole team goes further

PCS and Subcarriers: Dynamic Bandwidth Allocation

100 100 100 100 100 100 100 100

Impairments

DBA Enables:Higher data rate over a given distance

Go further at a given data rate

100 100 100 100 100 100 100 100100 100 100 100 100 100 100 10085 90 110 115 115 110 90 85

But there is a theoretical limit

C = B log2( )1 +S

Current options revolve around the two different parts of the Shannon Equation

The “bandwidth term” The “log term”

This is why SDM is so interesting for the near future

Bandwidth term

Log term

Capability

The Future of Submarine Networks

A Situation Report

Submarine network demand continues to grow

C = B log2( )1 +S

PCS brings us close to the Shannon Limit

1: Maximize ROI from existing cables 2: More to extract from new cables

What do we know? What does that mean?

←C-Band EDFA→

←C-Band EDFA→←L-Band EDFA→

←L-Band EDFA→

Amplifier Location

3: C+L delivers more capacity per fiber pair, not per cable

←C-Band EDFA→

Amplifier Location

4: SDM points the way to a Petabit transatlantic cable

What does a future transponder look like?

Imagine a future Petabit transatlantic cable

40 fiber pairs

25 Tb/s per FP

400 Gb/s per

Somehow you must deal with…

…transponders*

*At each end

What can we do to help?

C = B log2( )1 +S

There may be a Shannon Limit on fiber capacity…

…but not on power or volume

Imagine a 400G QSFP28 module that can span the Atlantic

Large Scale Photonic Integration

Implement many wavelengths on a single chip and mux them

Instead of one wavelength per transponder and then muxing them…

Mux or ROADM

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