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