This document discusses technologies for flexible, high-capacity optical networks, including ROADMs. It describes how ROADMs are used to manage traffic through optical network intersections. It then summarizes technologies like coherent Nyquist filtering, superchannels, flexible grid WSS, hybrid Raman-EDFA amplifiers, and multi-port flexgrid optical channel monitors that enable increased network capacity, reduced costs, and transparent wavelength management for 400Gb/s and 1Tb/s transmission. These improved ROADM subsystems will enable more future-proof ROADM architectures.

1. © 2014 Finisar Corporation
ROADM Technologies for Flexible, Tbit/sec Optical
Networks
Simon Poole
Director, New Business Ventures

2. © 2014 Finisar Corporation 2
ROADM Proliferation
 ROADMs are used to manage transparent traffic
through the intersections of a WDM network;
 3 prime functions:
 Wavelength Switching
 Amplification
 Signal Integrity Monitoring
2
Switching Cost Relative to OSI Layer

3. © 2014 Finisar Corporation 3
Problem: How to reduce cost of transmission
Increase Capacity
Coherent Nyquist Filtering
Superchannels Flexible Grid
Amplifiers Monitoring
Defragmentation etc
Dual WSS
Amplifiers
Reduce Capex
Route & Select
CD/CDC
Size
Power
Reduce Opex
Cost of Transmission
($/Gb/sec/km)

4. © 2014 Finisar Corporation 4
Increasing Capacity: Nyquist & Superchannels
 Third generation coherent
transmitters add a filtering
(digital/analog) at transmitter to
minimise optical bandwidth of
signal (Nyquist output)
 A superchannel is a multi-
carrier group of channels that
is operationally managed as a
single channel and which can
be presented to higher
networking layers as a single
higher data rate channel. (May
or may not be Nyquist filtered).
QPSK
RelativePower(dB)
Normalized Freq (GHz)
16QAM
RelativePower(dB)
Normalized Freq (GHz)

5. © 2014 Finisar Corporation 5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
-25 -20 -15 -10 -5 0 5 10 15 20 25
Rel Freq (GHz)
RelIL(dB)
-3.0
-2.5
-2.0
-22 -21 -20 -19 -18 -17
Rel Freq (GHz)
RelIL(dB)
Flexible Grid WSS
 First generation WSS allocated a
single channel to a single pixel
 LCoS-based WSS use a flexible
matrix-based wavelength switching
platform with megapixel matrices
which allows programmable
channel bandwidth

6. © 2014 Finisar Corporation 6
From Fixed-grid to Flexgrid
 LCoS technology allows arbitrary channel bandwidth
 Trade-off between flexibility and OSS requirements
 12.5GHz slices as per ITU G 694.1 (Feb 2012) supports legacy
fixed-grid as well as Flexgrid

7. © 2014 Finisar Corporation 7
Flexgrid & Superchannels
Flexgrid™ + superchannels with
Nyquist Filtering for maximum
Spectral Efficiency
Fixed Grid WSS require
interchannel guard-bands
35 GHz Pass Bands
15 GHz “Dead Zones”
Flexgrid™ WSS +
superchannels allow denser
channel packing by eliminating
inter-channel guard-bands
Up to 5 THz Pass Band, 15 GHz “Dead Zone”

8. © 2014 Finisar Corporation 8
Advanced Flexgrid Functionality
 No Limit to Superchannel spectral width
 37.5 GHz – 5 THz in 6.25 GHz increments
 Intra-channel attenuation control
 Attenuation range: 0 to 20 dB
 Intra-channel attenuation control of each 6.25 GHz section of a channel
 Enables equalization across super channels
 Dynamic and scalable channel width
 Hitlessly widen, narrow or migrate a channel with 6.25 GHz resolution
 Established traffic unaffected
 Simplifies defragmentation

9. © 2014 Finisar Corporation 9
Flexgrid WSS: a proven technology
 Finisar has deep experience in LCoS WSS since 2004
 More than half of Finisar’s shipped WSS feature flexible grid
functionality
 Common LCoS Platform
Single WSS: 1x4 – 1x20 Dual WSS: 2x1x20, 2xMxN

10. © 2014 Finisar Corporation 10
Example ROADM Configurations
 ROADM design depends on many factors
 Network Design
 Node Degree(s)
 Electronic vs Optical switching
 Expandability vs Initial Cost
 etc
 Traditional Broadcast and Select
 Colourless, Directionless (CD)
 Colourless, Directionless, Contentionless (CDC)

11. © 2014 Finisar Corporation 11
Broadcast and Select ROADM
 Passive split on Drop-side
 WSS on Add-side
 AWG for wavelength
mux/demux
 Fixed Grid
 Coloured Add/Drop
 100% Add/Drop of 88
channels
 2x100 GHz AWGs on
add side for lost cost
 Fixed-grid OCM
Classic (B&S) ROADMOCM
44 ch AWG
88 ch AWG44 ch AWG
1x9WSS
8x8 Span
Crossconnect
8x8 Span
Crossconnect
1x8splitter
88 ADD 88 DROP

12. © 2014 Finisar Corporation 12
Colourless, Directionless (CD) ROADM
 Typical Requirements
 8 degrees with 100% Add/Drop of 96
channels
 Flexgrid
 NB Limited drop-side filtering – only
works for coherent systems
 Typical Modularity
 Per degree
• 2x1x16 (Dual) WSS
• Flexgrid OCM
• Pre-amp and booster
 Per directional switch
• 2x6x8 per 96 channels
 Per 16 channel Add/Drop
• 2x1x16 splitter/couplers
• EDFA per splitter/coupler
CD ROADM
16x1 coupler
OCM
1x16WSS
8x8 Span
Crossconnect
8x8 Span
Crossconnect
1x16WSS
To
Directions 2-8
From
Directions 2-8
Drop Port 1
16 ADD 16 DROP
6x8 WSS 8x6 WSS
Drop Ports 2-8
AMP
x6 x6
Add 1
Add Ports 2 - 8
1x16 splitter
8x6 WSS
AMP

13. © 2014 Finisar Corporation 13
Colourless, Directionless, Contentionless, (CDC) ROADM
 Typical Requirements
 Scalable to 8 degrees with ~30%
Add/Drop of 96 channel systems
 Flexgrid
 NB No drop-side filtering – only
works for coherent systems
 Example Modularity
 Per degree
• 2x1x23 (Dual) WSS
• Flexgrid OCM
• Pre-amp and booster
 Per 16 channel Add/Drop
• 2x8x16 multicast switch
• Quad low-gain EDFA (2 per
multicast switch)
CDC ROADM
OCM
1x23WSS
8x8 Optical
Crossconnect
8x8 Optical
Crossconnect
1x23WSS
To
Directions 2 - 8
From
Directions 2-8
Drop Port 1
Drop Ports 2-16
16 ADD 16 DROP
AMP
AMP
Add Port 1
Add Ports 2-16
8x16 MCS8x16 MCS

14. © 2014 Finisar Corporation 14
8 Degree ROADM Comparison

15. © 2014 Finisar Corporation 15
CDC ROADM , 100% Add Drop
100% capacity on each Add/Drop
requires:
 1 x 4 splitter
 Higher gain amplifiers
 Additional MCS on Add/Drop
CDC ROADM
OCM
1x23WSS
8x8 Optical
Crossconnect
8x8 Optical
Crossconnect
1x23WSS
Drop Port 1
Drop Ports 2-16
Add Port 1
Add Ports 2-16
1x4 splitter
From
Directions 2-8
16 DROP
8x16 MCS
From
Directions 2-8
16 DROP
8x16 MCS
From
Directions 2-8
16 DROP
8x16 MCS
AMP

16. © 2014 Finisar Corporation
Optical Amplifiers: Size, Power, SNR

17. © 2014 Finisar Corporation 17
Honey, I shrunk the EDFA…
XFP: 1.5W power
consumption
APPROXIMATE LIFETIME EXPECTATIONS*
Coil diameter
(mm)
10 12 14 18
125µm – 3%
proof tested fiber
<1 year <1 year ~3.17 years >50 years
80µm – 2% proof
tested fiber
<1 year 0-3.17 years >40 years >50 years
80µm – 3% proof
tested fiber
>40 years >50 years >50 years >50 years
*Cost 218 Model, 4m of fibre

18. © 2014 Finisar Corporation 18
EDFA Arrays for ROADMs
 Shared electronics – reduces cost, power, size
 Uncooled pumps - lower power consumption
Dual EDFA (70x90 mm)
PreAmp and Booster in one box
8 EDFA
(183 x 150 x 18.5 mm)

19. © 2014 Finisar Corporation 19
Hybrid Raman-EDFA
 A combination of a counter-propagating Raman pump unit and a
variable gain EDFA
 Mesh networks
 ULH inline amplification
 Hut skipping (for high gain range units)
Overall Gain
Electronics for
AGC Control and Eye Safety
EDFA
980 Pump
Raman
14XX
pump(s)
2 or 3-Pump Hybrid Raman EDFA

20. © 2014 Finisar Corporation 20
Amplifier Trends
 Availability of up to 130 channels (37.5 GHz-spaced Nyquist
channels within larger superchannels) in the C-band drives
higher amplifier output powers.
 Mesh topology will drive lower NF (Hybrid Raman-EDFA)
and superior dynamics (fast electronics) to allow flexibility in
network re-configuration.
 Raman and Hybrid Raman-EDFAs will proliferate in long
haul systems.
 To simplify ROADM control loops, gain uniformity <0.5 dB.
 To reduce types of EDFAs used, either gain switched
platforms will proliferate or pluggable EDFAs will take off -
provided there is no cost penalty

21. © 2014 Finisar Corporation
Optical Channel Monitors:
Flexgrid, Superchannels and SDN

22. © 2014 Finisar Corporation 22
OCM Requirements
 Spectral power information with high resolution
 Intra-channel attenuation in 6.25 GHz spectral slices
 Power monitoring of superchannel carriers
 Location of center wavelengths of superchannel carriers
 Eliminate power differential between adjacent channels
 Fast scanning and response time
 Superchannel Add/Drop requires OCM, not just a photodiode, to monitor traffic through
Add/Drop paths
 Loss of Signal (LoS) and fault detection to support protection and restoration switching
 Staring mode - monitoring a fixed frequency
 Applications utilizing in-band modulation signals, i.e. wavelength tracking
• Possibly demodulate within the OCM
 Some proprietary OSNR measurement techniques

23. © 2014 Finisar Corporation 23
Multi-port Flexgrid Optical Channel Monitor
 Grating spectrally disperses light from up to four fibers.
 2D MEMS mirror is used to scan the optical spectrum onto an
array of photodiodes.

24. © 2014 Finisar Corporation 24
Example: Multiport Flexgrid OCM
 Small size: 100x50x15 mm, Low power: <5 W
 Parallel scanning of all ports in 500 ms; no need for dedicated switch
 Requires deconvolution of measured signal to provide 6.25 GHz slices
required for attenuation control on Flexgrid WSS
2-4 port OCM

25. © 2014 Finisar Corporation 25
To Summarise…
Improved ROADM subsystems
(Dual WSS, Hybrid amplifiers, Flexgrid OCM, etc) will
enable future-proof ROADM Architectures
to provide transparent Wavelength Management
Capability for future 400 Gb/sec and 1 Tb/sec