This presentation, delivered at Submarine Networks World Singapore 2015 (9-10 September 2015 – Singapore), reviews the recent developments in unrepeatered technologies (the 600 km barrier at 100G is now overcome!) and exposes how advanced single-span transmission technologies can be applied to several applications, including terrestrial backhaul and DCI networks at 100G and 400G channel rates.

1. © 2015 Xtera Communications, Inc. Proprietary & Confidential 1
Unrepeatered Systems:
Farther, Faster Over a Single Span
9 September 2015
Philippe A. Perrier

2. © 2015 Xtera Communications, Inc. Proprietary & Confidential 2
Innovative Unrepeatered Offering Confidential – Xtera Communications, Inc. Proprietary
Example of Driver for Longer Single-Span Systems
PoP
Cable Landing Station
Submarine cable
Terrestrial extension
City A
City B

3. © 2015 Xtera Communications, Inc. Proprietary & Confidential 3
Innovative Unrepeatered Offering Confidential – Xtera Communications, Inc. Proprietary
Example of Driver for Longer Single-Span Systems
(Cont’d)
City A
City B
BMH
BMH
PoP
Submarine cable
Terrestrial extension
• Because unrepeatered systems are loss-limited,
there is a direct link between capacity and reach performance

4. © 2015 Xtera Communications, Inc. Proprietary & Confidential 4
1. Fiber:
– Lower attenuation fiber is always better  Ultra low-loss (G.652B, G.654B)
– Type  Fibers with large effective area tolerant to higher launched power
2. Line rate
Modulation format
Pulse shaping
Channel density
Wavelength of transmission (fiber attenuation lower in L-band)
Detection (direct / coherent)
Forward Error Correction (Hard-Decision FEC / Soft-Decision FEC)
3. Power management
– Launched power; power in the line fiber
– Non-linearities mitigation
Maximizing Reach in Single-Span Systems
Tool Kit
  

5. © 2015 Xtera Communications, Inc. Proprietary & Confidential 5

4. Raman amplification
– Results from the interaction of an optical radiation (“pump”) with molecular
vibrations of the glass
• Maximum gain at a shift of ~ 100 nm in the 1550 nm window
– In any fiber types
– The more pump power the more gain
– Raman gain improves with lower
fiber attenuation (larger Leff)
Thus the NF and OSNR improvements
due to Raman will be larger in lower
attenuation fiber at the same
Raman pump power.
Maximizing Reach in Single Span Systems
Tool Kit (Cont’d)



0
1
3
4
5
6
6 12 18 24 30 36 42
2
0
48
Frequency shift (THz)
Ramangain(a.u.)
Pump
Resulting gain
~ 100 nm


6. © 2015 Xtera Communications, Inc. Proprietary & Confidential 6
Raman Amplification
Power Profile along the Span (Backward Raman)
266 km (61.2 dB); G.652D
Gain from backward
Raman pumping
Fiber attenuation
15x100G

7. © 2015 Xtera Communications, Inc. Proprietary & Confidential 7
Raman Amplification
Power Profile along the Span (BWD & FWD Raman)
288 km (65.5 dB); G.652D
Gain from backward
Raman pumping
Fiber attenuation
15x100G
Gain from
forward
Raman
pumping

8. © 2015 Xtera Communications, Inc. Proprietary & Confidential 8

5. Remote Optically Pumped Amplifier (ROPA)
– Passive sub-system, made up of a few optical components (housed in an
enclosure jointed to the cable) and pumped from one end of the span
(typically, receive end)
– Basically, performs the function of a mid-span EDFA
– More pump power allows ROPA to be located further away from the terminals
Maximizing Reach in Single Span Systems
Tool Kit (Cont’d)



ROPA
Erbium
doped
fibreSignal
in
Signal
out
Optical pump (from the
receive terminal)
~ 100 km



9. © 2015 Xtera Communications, Inc. Proprietary & Confidential 9
ROPA
Power Profile along the Span
373 km (76.1 dB); G.652B
Gain from backward
Raman pumping
Fiber attenuation
15x100G
Gain from
forward
Raman
pumping
Gain
from
ROPA
ROPA
107 km

10. © 2015 Xtera Communications, Inc. Proprietary & Confidential 10
• Corning® Vascade® EX2000 (G.654B), Aeff=112 mm2
• Span loss = 90.2 dB (cable attenuation = 0.162 dB/km)
Unrepeatered 1x100G Transmission over 557km
Field Trial with Verizon Business
ROPA
Forward
Raman
pumping
Backward
Raman
pumping
Gain from
forward
Raman
pumping
Gain from
backward
Raman
pumping
Fiber attenuation
Gain
from
ROPA
Direction of
transmission
291 km 133 km
1 wavelength
ROPA
133 km
Gain
from
ROPA
Perchannelpower(dBm)
Transmission distance (km)
EDFA

11. © 2015 Xtera Communications, Inc. Proprietary & Confidential 11
• EDFA only at transmit and receive sides
SD-FEC (15%; 6.4 dBQ threshold); target OSNR = 13.5 dB
Contribution of Key Techniques to
Transmission Performance – Baseline
340 km (55.5 dB)
Launched power = 14.8dBm
OSNR
Signal
ASE

12. © 2015 Xtera Communications, Inc. Proprietary & Confidential 12
 +56 km / +9 dB with respect to the baseline
Contribution of
Backward Raman Amplification
396 km (64.5 dB)
Launched power = 14.8dBm

13. © 2015 Xtera Communications, Inc. Proprietary & Confidential 13
 Extra +63 km / +10.3 dB
Contribution of
Forward Raman Amplification
459 km (74.8 dB)
DCM
Launched power = -4.4dBm

14. © 2015 Xtera Communications, Inc. Proprietary & Confidential 14
 Extra +67 km / +10.8 dB
Contribution of
Backward ROPA
526 km (85.6 dB)
Launched power = -4.4dBm
DCM
ROPA

15. © 2015 Xtera Communications, Inc. Proprietary & Confidential 15
 Extra +31 km / +4.6 dB
Contribution of
Forward ROPA
Launched power = -4.9dBm
DCM
ROPAROPA
557 km (90.2 dB)

16. © 2015 Xtera Communications, Inc. Proprietary & Confidential 16
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Power(dBm)
Wavelength (nm)
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Power(dBm)
Wavelength (nm)
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Power(dBm)
Wavelength (nm)
410 km (68.2 dB), 150 x 100G Unrepeatered
Transmission over G.654B Fiber
289 km
ROPA
121 km
Gain from
forward
Raman
pumping
Gain from
backward
Raman
pumping
Fiber attenuation
150 wavelengths
Gain
from
ROPA
Perchannelpower(dBm)
Transmission distance (km)
LRA (Discrete Raman amplifier) LRA
<Pout> = -2.8 dBm/ch <OSNR> = 14.2 dB

17. © 2015 Xtera Communications, Inc. Proprietary & Confidential 17
Innovative Unrepeatered Offering Confidential – Xtera Communications, Inc. Proprietary
Conclusion
PoP
Cable Landing Station
Submarine cable
Terrestrial cable
ROPA
ILA
• Not limited to single-span systems

18. © 2015 Xtera Communications, Inc. Proprietary & Confidential 18
• Span 1: G.654C fiber; 330 km (59 dB)
• Span 2: G.652D fiber; 300 km (59 dB)
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Power(dBm)
Wavelength (nm)
150 x 100G Transmission over Cascade of 2
Unrepeatered Spans (630 km, 118 dB)
ROPA
LRA LRALRA
Span 1
ROPA
Span 2
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Power(dBm)
Wavelength (nm)
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Power(dBm)
Wavelength (nm)
100 km110 km
<Q> = 7.0dB

19. © 2015 Xtera Communications, Inc. Proprietary & Confidential 19
Innovative Unrepeatered Offering Confidential – Xtera Communications, Inc. Proprietary
Conclusion
PoP
Cable Landing Station
Submarine cable
Terrestrial cable
ROPA
• Not limited to single-span systems
• Not limited to submarine space (e.g., terrestrial, DCI)

20. Maximizing Network Capacity, Reach and Value
Over land, under sea, worldwide
© 2015 Xtera Communications, Inc. Proprietary & Confidential 20