N-degree ROADM Architecture Comparison: Broadcast-and-Select vs Route-and-Select

OFC 2014, San Francisco CA (Th1I.2)

Mark Filer and Sorin Tibuleac

ADVA Optical Networking / Atlanta, GA

[email protected]

N-degree ROADM Architecture Comparison:Broadcast-and-Select vs Route-and-Select in 120 Gb/s DP-QPSK Transmission Systems

mailto:[email protected]

© 2014 ADVA Optical Networking. All rights reserved.22

• Increasing bandwidth demands high-capacity, spectrally-dense architectures in metro, regional, and long-haul systems

• Advent of: advanced modulation formats + all-optical switching fabric utilizing ROADMs

• Passband + isolation characteristics of ROADM WSSs critical

• Prior works: cascaded passband narrowing and crosstalk accumulation effects treated individually

• This work: addressing N-degree ROADM architectures• Broadcast-and-Select (B&S)

• Route-and-Select (R&S)

for N = {4,9} in 120 Gb/s coherent DP-QPSK systems considering passband and crosstalk effect simultaneously

Introduction


• Broadcast-and-Select:• broadcast passive 1xN splitter

followed by select Nx1 WSS• signals broadcast (i.e., copied)

onto all splitter output ports• signals selectively passed or

blocked at each select Nx1 WSS input port

• Route-and-Select:• route 1xN followed by select

Nx1 WSSs• signals selectively routed or

blocked to 1xN WSS output ports• signals selectively passed or

blocked at each select 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


to other degrees

from other degrees


drop add

• Broadcast-and-Select: reduced cost, power consump-

tion, and optical and electronic complexity

smaller BW-narrowing effect reduced isolation (higher

crosstalk leakage) IL scales with N

• Route-and-Select: increased cost, power consump-

tion, and optical and electronic complexity

larger BW-narrowing effect superior isolation (lower

crosstalk leakage) IL fixed regardless of N

ROADM Architectures – Pros/Cons

to other degrees

from other degrees

broadcast select WSS

drop add


-8dB

Back-of-envelope crosstalk calculation: isoWSS + 10∙log(N-1) + 10∙log(M ) example: isoWSS=-27dB, N=9, M=10

xtalk = -27dB + 9dB + 10dB = -8dB

• what are true requirements on isolation profile of stopband?

weighted crosstalk approach*

The Real Isolation Requirements?

-3dB

-27dB

modulated optical spectrum

port isolation

xM

* Filer and Tibuleac, Optics Express, Vol. 20, pp.17620-17631 (2012)

worst-case isolation

max # interferers

# cascaded ROADMs

N-d

egre

eselect WSS

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-16-17620


AOM

6x4x

120G co-herent Rx

demux

DSP

60-80kmNZ-DSF

120G DP-QPSK Tx

120G DP-QPSK xtalk

mux


block fcn

2x2

AO

M

Recirculating loop emulating system with 24 cascaded ROADM nodes

Experimental Configuration

• 120 Gb/s DP-QPSK real-time coherent XPDR


AOM

6x4x

120G co-herent Rx

demux

DSP

60-80kmNZ-DSF

120G DP-QPSK Tx

120G DP-QPSK xtalk

mux


block fcn

2x2

AO

M




• ROADM nodes with:• EDFA + VOA, and • 1 N-degree WSS (B&S config), or• 2 N-degree WSSs (R&S config)


AOM

6x4x

120G co-herent Rx

demux

DSP

60-80kmNZ-DSF

120G DP-QPSK Tx

120G DP-QPSK xtalk

mux


block fcn

2x2

AO

M





• 60-80km NZ-DSF, -6dBm/ch into fiber


AOM

6x4x

120G co-herent Rx

demux

DSP

60-80kmNZ-DSF

120G DP-QPSK Tx

120G DP-QPSK xtalk

mux


block fcn

2x2

AO

M





• 60-80km NZ-DSF, -6dBm/ch into fiber• uncorrelated 120 Gb/s DP-QPSK signal

as crosstalk source 120G DP-QPSK Tx

Fast Polar. Scrambler m

ux

120G DP-QPSK xtalk


AOM

6x4x

120G co-herent Rx

demux

DSP

60-80kmNZ-DSF

120G DP-QPSK Tx

120G DP-QPSK xtalk

mux


block fcn

2x2

AO

M





• 60-80km NZ-DSF, -6dBm/ch into fiber• uncorrelated 120 Gb/s DP-QPSK signal

as crosstalk source• optional ‘block fcn’ WSS to emulate

blocking functionality of another degree’s route WSS for R&S case

‘block fcn’ isolation profile


• passband: slightly larger bandwidth on 4x1 higher expected passband penalty for 9x1

• isolation: slightly better on 9x1 higher expected crosstalk penalty for 4x1

Experimental Configuration - WSS Profiles


• R&S experiences twice the number of passbands as B&S• evident in 3dB BW evolution vs

number of ROADMs

• BW curves translated roughly by factor 2x for R&S vs B&S

Cascaded Passband EvolutionR&S

B&S

4x1 9x1

B&S

R&S

4x19x1


after 24 ROADMs

• Plot of crosstalk vs number of ROADMs shows significant advantage of R&S architecture

• As expected, 4x1 slightly worse

• OSNR penalties may be computed by knowing crosstalk tolerance of modulation format

Cascaded Crosstalk Evolution

Broadcast-and-Select Route-and-Select

4x19x1

B&S

R&S

9x1 9x1


4x19x1

B&S

R&S

predicted from weighted crosstalk calculations

4x19x1

B&S

R&S

Cascaded Crosstalk Evolution


• Passband-only (solid): expected worse performance for R&S vs B&S due to twice the amount of passband narrowing

• As predicted, slightly higher penalty for 9x1 due to tighter passband

• Passband + crosstalk (dotted): additional degradations due to crosstalk accumulation as predicted by weighted crosstalk analysis:

• additional 0.05 to 0.2 dB penalty for B&S

• no additional penalty for R&S

• Overall performance better for B&S than R&S

Experimental Results

R&SB&S

R&SB&S


• Studied combined effects of passband and isolation characteristics of Nx1 WSSs for 120 Gb/s DP-QPSK transmission

• Both Broadcast-and-Select (B&S) and Route-and-Select (R&S) ROADM architectures were considered

• System OSNR penalties dominated by passband narrowing; overall penalties lower for B&S than for R&S by up to:

• 0.2 dB for 4x1• 0.5 dB for 9x1

• B&S preferred architecture for ROADM nodes of N≤9 in 120 Gb/s DP-QPSK systems

• For N>9, R&S architecture desirable due to:• fixed insertion loss inherent to R&S (doesn’t scale with N)• enhanced isolation over the larger number of potential interferers

• Further work to be done to understand complexities and tradeoffs for, e.g., Nyquist pulse shaping, ~baud-rate channel spacing

Conclusions

OFC 2014, San Francisco CA (Th1I.2)

[email protected]

Thank you.

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Technology

N-degree ROADM Architecture Comparison: Broadcast-and-Select vs Route-and-Select