1. Enabling Technologies and Challenges in Coherent Transport Networks
David Dahan, Ph.D.
ECI Telecom Ltd.

2. Drivers and Impact for Optical Networking Ecosystem
Other IP Traffic
IP Video
Traffic
90%
Video and more Video….
Internet streaming
IP at 5x 2008 levels with 90% Video
Shifting to the Cloud…
Enterprise and personal IT are moving to the cloud computing
Service Providers become “All Play” providers…
Exponential Traffic Growth
Dynamic Traffic Networks
Slow Revenue Growth
Technology challenges
Need more optical channel capacity : 100G/400G/1T
Reduce cost /bit/switch/transport
Business challenges
Improve service provisioning, time and resource utilization : SDT/ROADM/SDN

3. Optical Network Evolution
History and roadmap
2015-
2012
2011
2008
400G/1T
Superchannel
Bandwidth on Demand
N:M ROADM configuration
Gridless ROADM
400G/1T transceivers
Fully automated network
40G/100G
Coherent
100G Coherent networks support
DCFless networks
Colorless / directionless / contentionless
WSON GMPLS-based
40G
80 Channels
IP over WDM
Mesh topology
ASON GMPLS-based
ODU basednetworks
10G/40G channels, ready for 100G coherent
Plug and play
2006
10G
40 Channels
SDH / Sonet / EoS services support
Ring topology
East/west protection
Reconfigurable OADM
WDM over OTN
10G channels
SDH / Sonet Networks
Increase capacity
Point-to-point
CWDM/DWDM
Up to 40 channels
2.5/10G channels
2.5G
CWDM, DWDM
Continued demand for bandwidth from all applications

4. From Direct Detection to Coherent Detection
Up to 10G (SE = 0.2 b/s/Hz)
40G/100G/200G coherent solution
(SE > 2 b/s/Hz)
Intradyne Coherent detection
Phase and polarization diverse receiver
Frequency Locked Lasers (<+/- 2 GHz)
Digital Signal Processing at TX/RX TX RX
40G non coherent solution (SE = 0.8 b/s/Hz)

5. Current 100G Coherent Transceiver architecture
Modulation format : DP-QPSK
(Symbol Rate is ¼ Bit Rate : 2bit/s symbol x 2pol)
Integrated Coherent receiver
Integrated PDM QPSK MZM LiNBO3 Modulator
40 nm CMOS ASIC
with 4 (8 bit resolution) x63 Gsamples/s ADC
* Nelson et al, “A Robust Real-Time 100G Transceiver With Soft-Decision Forward Error Correction” J. OPT. COMMUN. NETW, vol 4, no. 11,2012

6. Current 100G Coherent Transceiver architectureIx Qx Qy Iy
DSP block
ADCs
Coh. Rx S LO
90°
Hybrid
& Detector j
Frequency & phase recovery
Slicing
Clock recovery &Interpolation
Resampling
Soft Symbol estimation
SD- FEC decoder
120G
OTU4
112G
D>60000 ps/nm
PMD>30 ps
1 bit +reliability bit info
6-8 bits
Gen
Type
Code
FEC Over
head
Pre-FEC BER TH. For post FEC<10-15
Coding gain [dB]
1st HD
BCH (Bose-Chaudhuri-Hocquenghem)
and RS (Reed-Solomon) codes 7%
~10-4
6-7 dB
2nd
Concatenation of RS codes, Viterbi convolutional codes and BCH codes (CBCH)
~1x10-3
(EFEC) dB
3rd SD
BCT (Block Turbo code) or Turbo Product Code (TPC) and LDPC (Low Density Parity Check) codes
15%-20%
~2x10-2 dB

7. 100G submarine Field trial over 4600 km
The 100G trial was carried out over Bezeq International’s live operational submarine fiber, in conjunction with the TeraSanta Consortium : demonstration of advanced capabilities of ECI 100G transmission system and technologies in compensating for non-linear channel impairments and chromatic dispersion utilizing advanced SD-FEC algorithms. 
DMUX
100G
Apollo Platform
100G
MUX

8. Flexgrid tunable laser
Next Generation of Coherent Transceiver : : Software Defined Transceiver (SDT)
Si Photonics IC with Electronic and Optical functionality
28 or 20 nm CMOS ASIC with DAC/ADC and DSP capabilities in both TX/RX
Power reduction
Higher computational strength
Adapt modulation format/Symbol rate
Technol.
Gate
ADC (8bits)
DAC
(8bits) GA
28 nm M
GS/s
1.7W
0.7W
2013
20 nm M
1.2W
0.5W
2014
Client Data Rate
100G/150G/200G/400G/1T
FEC
overhead
0%-30%
Modulation format
BPSK/QPSK/
8-QAM/16QAM TX
DSP
Pulse Shaping
Optical Carrier
Flexgrid tunable laser
(C/L band)

9. Raised Cosine FIR filter
New DSP features
Nyquist spectral shaping at TX : increases of the spectral efficiency by reducing the channel bandwidth to ~ symbol rate
Raised Cosine FIR filter

10. New DSP features Self diagnostic monitoring features :
Accumulated Chromatic Dispersion monitor
PMD monitor
OSNR monitor
ESNR monitor
Still missing : Efficient nonlinear compensation technique
Current state of the art techniques based on digital back propagation or Volterra Series are too complex for real time ASIC implementation
Nonlinear optical impairments are the ultimate limitations in optical network

11. Transmission Technology options for 400 Gb/s
Modulation
Gbit/s
OSNR min [dB]
DP-QPSK
120
12.5
DP-16QAM
240
18.5
480
21.5
DP-256QAM
>30 f
4x120G
4 bands with DP-QPSK (30Gbaud)
No spectral efficiency improvement over 100G
Suitable for long haul (>2000 km)
Symbol Rate
Limitations of DACs/ADC and electronics
90 Gbaud
60 Gbaud
1x480G
1 bands with DP-16 QAM (60 Gbaud)
High spectral efficiency
Reach Limited to Metro (~700 km)
30 Gbaud
2 bands with DP-16 QAM (30 Gbaud)
High spectral efficiency
Reach Metro /Long Haul distances f
2x240G
1 bands with DP-256 QAM (30 Gbaud)
Extremely high spectral efficiency
Reach Limited (~100 km) f
1x480G
QPSK
8-QAM
16-QAM
32-QAM
64-QAM
256-QAM
Constellation size 1
Reach Limited <<100km 2 3 4
Subcarriers/band

12. Hybrid Raman Amplifiers
Improving transmission reach
Complex Coherent modulation formats like 200G DP-16QAM require for 6-8 dB OSNR improvement with respect with current 100G DP-QPSK modulation format
The use of hybrid Raman-EDFA amplification schemes is required to improve the received OSNR or mitigate the nonlinear penalties by lowering the launched power into the fiber : can improve the transmission reach by 100%
Non linear impairments
Low OSNR
With Hybrid Raman –EDFA amplification
Non linear impairments
Low OSNR
Non linear impairments
Low OSNR

13. Improving spectral efficiency beyond 100G
Superchannels
Improving spectral efficiency beyond 100G
Future services of 400Gb/s and 1T will be packed into super channels, in order to provide optimum flexibility and reach performance tradeoffs :
400G : 2 channels spaced by 37.5 GHz
1T : 5 channels spaced by 37.5 GHz
For optimized spectral efficiency, Super channels use Nyquist spectral shaping and Flexgrid WSS ROADMs

14. Flexgrid Networks
To increase spectral efficiency, we move from a fixed channel grid (50GHz/100GHz) to flexible channel grid management :
6.25 GHz grid
12.5 GHz bandwidth granularity
The channel spectral slot is adapted on a per channel basis using :
10G/ 40G on 25 GHz slot
100G and 200G on 37.5 GHz slot
400G on 75 GHz slot
1T on GHz slot
400G 1T
100G
50 GHz f
Fixed 50GHz grid
10G
40G
50 GHz
400G 1T
100G f
Flex grid
40G
10G
Increase by 25 % the available useable fiber bandwidth

15. Flex Grid Technology enablers
Very stable tunable lasers compatible with 6.25 GHz grid resolution
Flexgrid ROADMs :
First generation of WSS allocated a channel on a single MEM based pixel
Flexible WSS based on LCoS technology use a flexible matrix based wavelength switching platform with megapixel matrices allowing programmable channel bandwidth
* EXFO Webinar : “400G Technologies: the new challenges that lie ahead”,04/02/2014

16. Optical Network Node with Full Flexibility
Network node capabilities are enhanced with new features allowing full flexibility :
Flexgrid : any channel/ superchannel can be directed towards any other node
Colorless
Directionless
Contentionless
Flexgrid WSS

17. Optical Network Node with Full Flexibility
Network node capabilities are enhanced with new features allowing full flexibility :
Flexgrid
Colorless : any wavelength can be added or dropped at any port
Directionless
Contentionless

18. Optical Network Node with Full Flexibility
Network node capabilities are enhanced with new features allowing full flexibility :
Flexgrid
Colorless
Directionless : any wavelength can be directed at any direction an reach a given port
Contentionless

19. Optical Network Node with Full Flexibility
Network node capabilities are enhanced with new features allowing full flexibility :
Flexgrid
Colorless
Directionless
Contentionless : Multiple channels of the same wavelength can be dropped or added by a single module

20. Optimum management of the optical spectrum resources
Optimized routing and resource allocation algorithms for flexible optical networking
Conventional Routing and Wavelength Assignment (RWA) algorithms can be used only for rigid grid networking
New paradigms based on Routing and Spectral allocation Assignment (RSA) algorithms should be developed for flexible grid networking
Physical Impairment awareness and optimal combination of Software Defined Transceiver parameters (modulation format/symbol rate, FEC overhead) will be required
Need to find optimum strategies for spectrum defragmentation
Rigid grid network
Flex grid network

21. Software Defined Networking : Why ?
Flexible Multi-layer Networking
Bandwidth hungry services (video, mobile data, cloud services) lead to new traffic characteristics :
Rapidly changing traffic patterns
High Pic to average traffic ratio
Large Data chunk transfers
Asymmetric traffic between nodes
SDN will turn the networks into programmable virtualized resource for better efficiency and automation

22. Software Defined Networking
Flexible Multi-layer Networking
Application requirements
Dynamic connectivity
Bandwidth
QoS
Resiliency
User I/Fs
Network Apps
Open APIs
SND Control Plane
Hardware Abstraction
& Virtualization
SDN Control Plane
Aware of Application requirement
Optimized resource and configuration
OpenFlow
Multi layer Network Elements
Ethernet switch/MPLS router
OTN switch
ROADM, SDT
Fiber switch
Multi layer network elements

23. Conclusion The future optical transport networking will provide better
Capacity : coherent modulation formats, superchannel, better SE
Flexibility : software defined transceivers, flexible grid, flexible CDC ROADMs nodes
Resource utilization : impairment aware- RSA algorithms, SDN
The future optical transport networking needs to provide :
Efficient nonlinear optical impairment compensation techniques
Strategies for pro-active and re-active spectrum defragmentation and fragmentation awareness in service expansion and contraction policies
Energy efficient strategies
Capex and Opex reductions