October 1, 2012
Sheldon Walklin
CTO, Optelian

Contents
• Introduction
• Wavelength Selective Switch
• Colorless, Directionless and Contentionless
• Flexible Bandwidth ROADMs and Transmission
Beyond 100 Gb/s
• ROADM Control, OpenFlow and SDN
• Conclusion
2
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Wavelength Selective Switch Functionality
Nx1 WSS
SW 1
VOA 1
Port 1
Common
SW M
VOA M
Port N
3
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Colorless, Directionless and Contentionless (CDC)
Colorless
Any wavelength can be dynamically added/dropped without having to re-fiber a transceiver.
Directionless
A wavelength can be dynamically added/dropped from any direction without having to re-fiber a transceiver.
Contentionless
A wavelength can be re-used on all directions without any restrictions.
4
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4-Degree ROADM (Colored)
Com
In
B
Com
Out
WSS
Com
In
A
Com
Out
Com
In
Com
Out
C
•
In general, can build an N-degree
ROADM using
Nx1 WSSs and
1xN splitters.
• The color and direction are fixed by fiber connections.
A B
. . .
C D
. . .
. . .
. . .
Colored add ports
Com
In
D
WSS
Com
Out
A
. . .
B
. . .
C
. . .
Colored drop ports
D
. . .
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Transceiver
Rx
Tx

4-Degree ROADM (Colorless)
Com
In
A
Com
Out
Com
In
B
Com
Out
WSS
Com
In
Com
Out
C
A B C D
. . .
. . .
. . .
Colorless add ports
. . .
Com
In
D
WSS
Com
Out
© 2011 Optelian. All rights reserved.
A
WSS
. . .
WSS
. . .
B C
WSS
. . .
D
WSS
. . .
Colorless drop ports
Transceiver
Rx
Tx
6
•
Any transceiver wavelength
(color) can be remotely configured
• The direction is fixed by fiber connections.
•
Reduced number of access ports compared to colored.

Colorless and Directionless
Drop directions
A B C D
Add directions
A B C D
4x1 WSS
1xN WSS
. . .
Colorless drop ports
Wavelength
Contention
Passive combiner
. . .
Colorless add ports
•
Structure for cross connecting between degrees remains the same as shown for the 4-degree
ROADM on earlier slide.
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7

Colorless, Directionless and Contentionless
(using NxM WSSs) drop directions
A B C D
4xN WSS
. . .
add directions
A B C D
Nx4 WSS
. . .
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Colorless, Directionless and Contentionless
(using Broadcast-and-Select with Tunable Filters)
Drop directions
A B C D
Add directions
A B C D
4x1
SW
4x1
SW
TF TF
CDC drop ports
4x1
SW
TF
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4x1
SW
4x1
SW
CDC add ports
4x1
SW

Colorless, Directionless and Contentionless
(using Adjunct NxM Photonic Switches)
B
Com
In
Com
Out
WSS
•
Use NxM photonic switches to upgrade existing colored
ROADMs to full CDC functionality
Com
In
A
Com
Out
Com
In
Com
Out
C
A
. . .
B
. . .
C
. . .
D
. . .
Com
In
Colorless add ports
D
WSS
Com
Out
A
. . .
B
. . .
C
. . .
D
. . .
Colorless drop ports
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Transceiver
Rx
Tx

Ideal CDC WSS
A
Directions
B C
CDC drop ports
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CDC ROADM
(module)
D
•
Concept module
•
Non-blocking wavelength switching between any set of ports.
• Per wavelength attenuation control at line egress ports.
• Low insertion loss (up to a few dB)
• Very high reliability.
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CDC add ports

The Benefit of CDC Functionality s1
R1 s3
R2 s2 s4
R3 s5 s10
R5
R4 s7 s11 s6 R6
R7 s8 s12 s9
R8
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12
•
Without CDC, cannot automatically restore optical circuit for failure on Span S1 or
S6, or power failure at Node R2 or R4.
• CDC allows more flexibility to remotely reroute optical circuit when optimizing network utilization.
•
Consideration: OTN and/or
Layer 2+ protection and switching capabilities may reduce need for optical circuit dynamic routing.

Flexible Bandwidth ROADMs
 1  2  3  4  5  6
Ch1 Ch2 Ch3 Ch4 Ch5
• Flexible bandwidth (FB) ROADMs (aka gridless ROADMs) allow the passband center and/or width to be dynamically adjusted.
•
Many people advocate that FB ROADMs will be required to support bit rates beyond 100G.
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Considerations for Transmission
Beyond 100 Gb/s
• For 40G and 100G transmission, the client interface has transitioned to parallel optics, while the line interface has retained single-carrier optics for improved transmission capacity. Parallel optics will likely be required on the line interface for bit rates approaching 1 Tb/s and beyond.
• Multi-carrier channels or superchannels are likely to be used for longhaul transmission beyond 100 Gb/s, with PDM-QPSK used for each constituent carrier. PDM-xQAM may be used in Metro (shorter distance) applications.
• Although FB ROADMs may provide improved spectral efficiency, they are not required for transmission beyond 100 Gb/s.
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ROADM Control
Automated Optical Layer
• Controls the power level of each wavelength at ROADM ports to a set target (Automatic Power Balancing)
• Span or link gain control
Automated Wavelength Circuit Provisioning
• Impairment-aware path computation (wavelength routing)
• ROADM switch configuration
15
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Automated Wavelength Circuit Provisioning
5 done
1 wavelength circuit request
Connection
Controller
4 signaling
2
A-to-Z circuit request with routing constraints viable route(s) and required regen location(s)
3
Path
Computation
Element impairment-aware
Optical
Network
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16

OpenFlow and SDN
App
OpenFlow
Controller s1
R1 s3
R2 s2 s4
R3 s5 s10
R5
R4 s7 s11 s6 R6
R7 s8 s12 s9
R8
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App
App
17
• Centralized dynamic control
•
Simple flow table entry at each ROADM for wavelength connection
•
Smart Apps
– must be aware of topology, resource availability and state, fiber properties, impairment modeling, etc.
•
Opportunity for OpenFlow applications to have multilayer control and visibility
•
Apps can evolve independently of physical network

Conclusion
• Current generation ROADMs use WSS modules and have colored or colorless access ports.
• CDC functionality generally has a higher capital cost and lower access port density, but may provide lower operational costs.
• FB ROADMs may provide improved spectral efficiency, but are not required to achieve transmission beyond 100 Gb/s
• Multi-carrier channels or superchannels will likely be used for long-haul transmission beyond 100 Gb/s, with PDM-QPSK used for each constituent carrier. PDM-xQAM may see application in the Metro
• Automated ROADM networks are well-suited to centralized control, making OpenFlow a good match. This could also facilitate multi-layer control.
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© 2011 Optelian. All rights reserved.