Check out Mark Filer and Sorin Tibuleac's IEEE IPC 2013 slides on performance tradeoffs of 120 Gb/s DP-QPSK in ROADM systems employing broadcast-and-select versus route-and-select architectures

1. IPC 2013, Bellevue WA (WG1.2)
Mark Filer and Sorin Tibuleac
ADVA Optical Networking / Atlanta, GA
mfiler@advaoptical.com
Performance Tradeoffs of 120 Gb/s DP-
QPSK in ROADM Systems Employing
Broadcast-and-Select Versus Route-
and-Select Architectures

2. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Introduction
• Increased capacity demands require optical transmission through
spectrally-dense ROADM-enabled networks
• Increasingly challenging due to high bit-rate signals with
bandwidths on the order of the channel spacing (e.g., 100G)
• Passband and isolation characteristics of WSS become critical –
must be accounted for properly in system architecture and design
• ROADM architecture options:
• Broadcast-and-Select (B&S)
• Route-and-Select (R&S)
• Passband narrowing and crosstalk accumulation effects have been
treated separately in prior work
• This study: performance of 120 Gb/s coherent DP-QPSK in a
ROADM-enabled network considering both impairments
simultaneously

3. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
• Broadcast-and-Select:
• passive 1xN splitter followed by
single Nx1 WSS
• signals broadcast (“copied”)
onto all splitter output ports
• signals selectively passed or
blocked at each Nx1 WSS input
port
• Route-and-Select:
• 1xN followed by Nx1 WSSs
• signals selectively routed or
blocked to 1xN WSS output
ports
• signals selectively passed or
blocked at each Nx1 WSS input
port
ROADM architectures
to other
degrees
from other
degrees
broadcast select WSS
drop add
to other
degrees
from other
degrees
route WSS select WSS
drop add

4. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
to other
degrees
from other
degrees
route WSS select WSS
drop add
• Broadcast-and-Select:
 reduced optical/electronic
complexity, cost, power
consumption
 lower passband narrowing
 reduced isolation (higher
crosstalk leakage)
 high IL for large N
• Route-and-Select:
 increased optical/electronic
complexity, cost, power
consumption
 increased passband narrowing
 superior isolation (lower
crosstalk leakage)
 acceptable IL for large N
ROADM architectures (2)
to other
degrees
from other
degrees
broadcast select WSS
drop add

5. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Isolation requirements?
• Total Crosstalk:
isoWSS + 10∙log(N-1) + 10∙log(M),
e.g., isoWSS=-27dB, N=9, M=10
Total Crosstalk = (-27dB) + (9dB) + (10dB)
= -8dB
• requirements on isolation profile of
stopband?
•  “weighted” crosstalk approach*
Nx1 WSS
modulated optical spectrum
port isolation
xM
* Filer and Tibuleac, Optics Express, Vol. 20, pp.17620-17631 (2012)

6. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
AOM
6x
4x
120G co-
herent Rx
demux
DSP
60-80km
NZ-DSF
120G DP-
QPSK Tx
120G DP-
QPSK xtalk
mux
route WSS select WSS
block fcn
2x2
AOM
Experiment
Recirculating loop
emulating system
with 24 cascaded
ROADM nodes
• 120 Gb/s DP-QPSK coherent XPDR
• 4x ROADM nodes with EDFA, VOA, and
1 or 2 N-degree WSSs (configurable to
R&S or B&S architecture)
• 60-80km NZ-DSF*, -6dBm/ch into fiber

7. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
AOM
6x
4x
120G co-
herent Rx
demux
DSP
60-80km
NZ-DSF
120G DP-
QPSK Tx
120G DP-
QPSK xtalk
mux
route WSS select WSS
block fcn
2x2
AOM
Experiment
Recirculating loop
emulating system
with 24 cascaded
ROADM nodes
• 120 Gb/s DP-QPSK coherent XPDR
• 4x ROADM nodes with EDFA, VOA, and
1 or 2 N-degree WSSs (configurable to
R&S or B&S architecture)
• 60-80km NZ-DSF*, -6dBm/ch into fiber
• uncorrelated 120 Gb/s DP-QPSK XPDR
as crosstalk source
120G DP-
QPSK Tx
Fast Polar.
Scrambler
mux
120G DP-QPSK xtalk

8. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
AOM
6x
4x
120G co-
herent Rx
demux
DSP
60-80km
NZ-DSF
120G DP-
QPSK Tx
120G DP-
QPSK xtalk
mux
route WSS select WSS
block fcn
2x2
AOM
Experiment
Recirculating loop
emulating system
with 24 cascaded
ROADM nodes
• 120 Gb/s DP-QPSK coherent XPDR
• 4x ROADM nodes with EDFA, VOA, and
1 or 2 N-degree WSSs (configurable to
R&S or B&S architecture)
• 60-80km NZ-DSF*, -6dBm/ch into fiber
• uncorrelated 120 Gb/s DP-QPSK XPDR
as crosstalk source
• optional block fcn WSS to emulate
blocking function of another degree’s
‘route’ WSS for R&S case

9. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
CW DFB
sources
AOM
6x
4x
120G co-
herent Rx
demux
DSP
60-80km
NZ-DSF
120G DP-
QPSK Tx
120G DP-
QPSK xtalk
mux
route WSS select WSS
block fcn
2x2
AOM
Experiment
Recirculating loop
emulating system
with 24 cascaded
ROADM nodes
• 120 Gb/s DP-QPSK coherent XPDR
• 4x ROADM nodes with EDFA, VOA, and
1 or 2 N-degree WSSs (configurable to
R&S or B&S architecture)
• 60-80km NZ-DSF*, -6dBm/ch into fiber
• uncorrelated 120 Gb/s DP-QPSK XPDR
as crosstalk source
• optional block fcn WSS to emulate
blocking function of another degree’s
‘route’ WSS for R&S case
• additional unmodulated CW sources
coupled in to maintain constant
amplifier gain during loop transitions

10. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Cascaded passband evolution
• R&S – experiences twice the
number of passbands as B&S
• Reflected in 3dB-BW evolution vs
# ROADMs
• BW vs # ROADMs curve shifted
by factor 2x for R&S compared to
B&S
Broadcast-and-Select Route-and-Select

11. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
4 ROADMs8 ROADMs12 ROADMs16 ROADMs20 ROADMs24 ROADMs
• Plot of crosstalk vs # ROADMs
shows great crosstalk
advantage of R&S architecture
• OSNR penalties may be
computed by knowing crosstalk
tolerance of modulation format
Cascaded crosstalk evolution
Broadcast-and-Select Route-and-Select

12. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Cascaded crosstalk evolution

13. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Results
• Expected worse performance for R&S vs B&S due to additional
passband narrowing
• Additional degradations due to crosstalk accumulation as
predicted by weighted crosstalk analysis:
• 0.05 to 0.2 dB for B&S
• 0 dB for R&S
• Overall performance better for B&S than R&S

14. © 2013 ADVA Optical Networking. All rights reserved. Confidential.IPC 2013, Bellevue WA (WG1.2)
Conclusions
• Combined penalties due to passband and isolation characteristics
of 9x1 WSSs were studied for 120 Gb/s DP-QPSK transmission
• Broadcast-and-Select and Route-and-Select ROADM architectures
considered
• Overall system penalties are lower for B&S than for R&S
configurations by up to 0.5dB
• B&S may be preferred architecture for ROADM nodes of N ≤ 9
• For N > 9, R&S architecture is desirable due to the higher
insertion loss inherent to B&S

15. IPC 2013, Bellevue WA (WG1.2)
Thank you.
mfiler@advaoptical.com
contact details: