Following a short update on the latest developments for unrepeatered subsea cable systems (150 x 100G on 410 km, 100G on 607 km), this presentation describes the genesis and the development of the industry’s most advanced subsea repeaters, with innovative electrical, optical and mechanical designs. This Raman-based repeaters was deployed by Xtera in May 2015, an industry’s first. This presentation was delivered at WDM & Next Generation Optical Networking EMEA 2015 conference (22-25 June 2015 – Nice, France).

1. © 2015 Xtera Communications, Inc. Proprietary & Confidential 1
Xtera Communications, Inc.
The Why’s and the How’s of
the Most Advanced Repeater
Herve Fevrier
24 June 2015

2. © 2015 Xtera Communications, Inc. Proprietary & Confidential 2
• Quick update on Unrepeatered Subsea
• Repeatered Subsea: the Why’s and How’s of
the most advanced repeater
Outline

3. © 2015 Xtera Communications, Inc. Proprietary & Confidential 3
• Recent Evolution
– Reach and Capacity x Reach
• Key Technologies
– Distributed Raman Amplification
– Remote Optically Pumped Amplifier (ROPA)
– Coherent Technology, DSP, FEC, …
– Ultra Low-Loss Fibers
• Going from 0.175dB/km to 0.155… means 400km goes to 450km!
NOTE: Only subsea applications here
Unrepeatered Subsea Communications
250
300
350
400
450
500
550
600
650
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
Distance
(Km)
Year
0
1
2
3
4
5
6
7
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
Capacity
x
Reach
(Pb/s
-­‐Km)
Year
(a)
(b)

4. © 2015 Xtera Communications, Inc. Proprietary & Confidential 4
• Cabled large Aeff fiber - G.654D fiber (Corning Vascade EX2000)
• Commercial DWDM equipment
• Transmit and Receive ROPAs on one fiber pair
• Advanced ROPA architecture
• 1 x 100G over 556.7 km (90.2dB) and 4 x 100G over 523.2 km (84.8dB)
Long Distance / Low Capacity Unrepeatered
100G MXP λ1
100G MXP λ2
100G MXP λ3
100G MXP λ4
WSS
DCU
EOA 289.3 km
or
255.8 kmROPA (F)
133.7 km
EOA
ROPA (B)
Residual
pump
sharing
WSS
Forward
Raman
Backward
Raman
100G MXP λ1
100G MXP λ2
100G MXP λ3
100G MXP λ4
ROPA (B)
ROPA (F)
p
P’
133.7 km
-50
-45
-40
-35
-30
-25
-20
1558 1560 1562 1564 1566 1568
Power(dBm)
Wavelength (nm)
Input-0.2nm RBW
Output-0.2nm RBW
-50
-45
-40
-35
-30
-25
-20
1557 1559 1561 1563 1565 1567
Power(dBm)
Wavelength (nm)
Input-0.2nm RBW
Output-0.2nm RBW
(a)
(b) (c)
ROPA (F)
ROPA (B)
ROPA (B)
ROPA (F)
Signal
Signal
Residual pump
sharing
Backward Pump
Backward Pump
Forward Pump
Forward Pump

5. © 2015 Xtera Communications, Inc. Proprietary & Confidential 5
• G.654D fiber (Corning Vascade EX2000)
• Wide-band distributed Raman amplification
• Receive ROPA
• 15 Tb/s (150 x 100G) unrepeatered transmission over 409.6 km (68.2
dB) covering 1531-1592nm spectrum
High Capacity Unrepeatered
45 C-Band
(odd) DFBs
30 L-Band
(odd) DFBs
45 C-Band
(even) DFBs
30 L-Band
(even) DFBs
100G
Comb
100G
Comb
100-GHz
PM-AWG
: PM 3dB (50/50) coupler
: 3dB (50/50) coupler
WSS-1
C-100G MXP
C-100G MXP
L-100G MXP
Backward
Raman
Forward
Raman
EX2000 409.6 km (68.2dB)
ROPA
120.9 km288.7 km
LRA-1 LRA-2 LRA-3
WSS-2
C-100G MXP
C-100G MXP
L-100G MXP
1525 1535 1545 1555 1565 1575 1585 1595
Wavelength (nm)
-25
-20
-15
-10
-5
0
5
1525 1535 1545 1555 1565 1575 1585 1595
Power(dBm)
Wavelength (nm)
(a)
(b) (c)
LRA-2 out LRA-3 out
12
14
16
18
20
22
24
1525 1535 1545 1555 1565 1575 1585 1595
OSNR(dB)
Wavelength (nm)
OSNR
for
10CHs
OSNR
for
30CHs
OSNR
for
50CHs
OSNR
for
100CHs
OSNR
for
150CHs
6
7
8
9
10
11
12
1525 1535 1545 1555 1565 1575 1585 1595
Q(dB)beforeFEC
Wavelength (nm)
Q
for
10CHs
Q
for
30CHs
Q
for
50CHs
Q
for
100CHs
Q
for
150CHs
(a)
(b)

6. © 2015 Xtera Communications, Inc. Proprietary & Confidential 6
• Extra pumping fibers
• Transmit and Receive ROPA
• 1x100G over 607 km (97dB) and 1x10G over 632 km (101dB)
Ultra-Long Unrepeatered
signal-path
pump-path1
Erbium, 20m
a b
c
pump-path2
pump λ1
pump λ2
signal
ab
c
a’
Erbium, 12m Erbium, 12m
signal
-path
pump-path1
pump-path2
(a)
WSS
327.6 km for 100G
352.6 km for 10G transmission
EDFA
DCU
EDFA
128.0 km
128.2 km
128.7 km
151.4 km
154.2 km
151.7 km
Forward
ROPA
Backward
ROPA
DCU
EDFA
DCU
EDFA
100G or
10G line card
For 10G
transmission
pump-path1
pump-path2
pump λ1
pump λ2
signal
signal-path : Total 607.0 km for 100G / 632.0 km for 10G transmission
100G or
10G line card
WSS
(c)
Forward ROPA
Backward ROPA
(b)

7. © 2015 Xtera Communications, Inc. Proprietary & Confidential 7
• Intermediate site can be a ROADM
• 8x100G over 2 spans: SMF 303.5km (59.7dB) and PSCF 342.9km
(60.8dB)
Unrepeatered over a Cascade
of Two Very Long Spans
Fwd Pumps Bkwd Pumps
8 x 120 Gb/s PM-QPSK SMF 303.5Km. 59.7dB
DFB
DFB
DFB
100G
Card
100G
Comb
DCM
PMMUX
EOAEOA Filter for ASE
suppression
Fwd PumpsBkwd Pumps
EOA
PSCF 342.9Km. 60.8dB
SMF 303.5Km PSCF 342.9Km
-35
-30
-25
-20
-15
-10
-5
0
5
1556 1558 1560 1562 1564 1566
Power(dBm)
Wavelength (nm)
Span-1 Input
Span-1 Output
Span-2 Output
(a)
(b)

8. © 2015 Xtera Communications, Inc. Proprietary & Confidential 8
Xtera Submarine Timeline:
Commitment and Innovation
1st repeatered
upgrade
1st unrepeatered
upgrade
1st redeployment
of repeatered cable
1st ROPA
1st turnkey project
1st 100G upgrade
of repeatered system
Xtera
incorporated
Azea
incorporated
NXT
10G LH rep.
Nu-Wave XLS
20G long-haul
repeatered
Xtera + Azea
Nu-Wave Optima
40G long-haul
repeatered
100G SD-FEC
100G long-haul
repeatered
Subsea repeater
• Commitment to the submarine market
• Innovation in technology and business approach
LOI for
9,400 km
system
557 km 100G
unrepeatered
Contract for
1,500 km
system
1st repeater
deployment
1998 2001 2004 2005 2006 2007 20112010 2012 2013 2014 2015
607 km 100G
unrepeatered

9. © 2015 Xtera Communications, Inc. Proprietary & Confidential 9
The Why’s of the Most Advanced Repeater
Capacity Scaling and Flexibility - What Next?
● Dry Plant - Getting close to Shannon limit
○ Minor tweaks in FEC, implementation penalties, some NL
compensation, flexible modulation but no game changers
● Wet Plant (some combination of these to get 4-10x
increase)
○ More spectrum (C+L bands) : Uses existing fiber cabling
infrastructure
○ More fibers : Needs re-engineering of cabling
infrastructure
○ More cores (SDM) : Needs significant maturity of
multicore fiber and component ecosystem
“No ...
(but wGoogle Confi
Capacity Scaling and Flexibility - What Next?
● Dry Plant - Getting close to Shannon limit
○ Minor tweaks in FEC, implementation penalties, some NL
compensation, flexible modulation but no game changers
● Wet Plant (some combination of these to get 4-10x
increase)
○ More spectrum (C+L bands) : Uses existing fiber cabling
infrastructure
○ More fibers : Needs re-engineering of cabling
infrastructure
○ More cores (SDM) : Needs significant maturity of
multicore fiber and component ecosystem
“No ...
(but w

10. © 2015 Xtera Communications, Inc. Proprietary & Confidential 10
Optical Repeater for Subsea
Cable Systems Launched at
Innovations:
Mechanical Marine grade titanium. Compact, light and strong.
Electrical Improved powering enabling Raman amplification.
Optical Modular optical design.
Optical bandwidth increased by 50%.
Manufacturability Flexible and simplified manufacturing process

11. © 2015 Xtera Communications, Inc. Proprietary & Confidential 11
• Down to 8,000m
• Up to 12kV
• Up to 8 fiber pairs
• Titanium alloy has strength comparable to that of steel, yet it is 45%
lighter
• The repeater is extremely compact and light and can pass through a
marine plough
• Optical amplifier modularity – up to 55nm optical bandwidth
• Reliability: < 10 FIT per amplifier pair
Xtera’s Repeater

12. © 2015 Xtera Communications, Inc. Proprietary & Confidential 12
Optical Characteristics
-­‐1
0
1
2
3
4
5
1540 1550 1560 1570 1580 1590 1600 1610
NF
(dB)
Wavelength
(nm)
-­‐4
-­‐3
-­‐2
-­‐1
0
1
2
3
1540 1550 1560 1570 1580 1590 1600 1610
Rel.
Gain
(dB)
Wavelength
(nm)
• Bandwidth > 55 nm
• Tilt of ±2 dB possible
• Noise figure <4dB

13. © 2015 Xtera Communications, Inc. Proprietary & Confidential 13
Repeater Manufacturing 1
!

14. © 2015 Xtera Communications, Inc. Proprietary & Confidential 14
Repeater Manufacturing 2

15. © 2015 Xtera Communications, Inc. Proprietary & Confidential 15
Repeater Transfer

16. © 2015 Xtera Communications, Inc. Proprietary & Confidential 16
Repeater Loading

17. © 2015 Xtera Communications, Inc. Proprietary & Confidential 17
Repeater Deployment (First Raman Repeater)

18. © 2015 Xtera Communications, Inc. Proprietary & Confidential 18
HUGO: Cable Re-lay for New Unrepeatered System
… later “upgraded” to a repeatered system!
Porthcurno
Guernsey
Lannion
282 km
189 km
A cable repair with a repeater
instead of a joint box!

19. © 2015 Xtera Communications, Inc. Proprietary & Confidential 19
• Long repeater spacing
• Completion planned in 2H 2015
US Department of Defense
New 1,500 km Repeatered Subsea Cable System

20. © 2015 Xtera Communications, Inc. Proprietary & Confidential 20
• Dry plant: More to come in 2015
– Flex-Rate card: 100 / 150 / 200G per optical carrier
– Improved performance: coherent technology, DSP, FEC, …
• Unrepeatered: Stay tuned 100G at 100dB soon…
(x2 each year for 10 years)
• Wet plant:
– Branching unit: first release this year
– Repeater: 70nm bandwidth (2017 deployment)
More capacity, More flexibility
Conclusion
Where are we going from here??

21. Maximizing Network Capacity, Reach and Value
Over land, under sea, worldwide
© 2015 Xtera Communications, Inc. Proprietary & Confidential 21