N-degree ROADM Architecture Comparison: Broadcast-and-Select vs Route-and-Select
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N-degree ROADM Architecture Comparison: Broadcast-and-Select vs Route-and-Select
- 1. OFC 2014, San Francisco CA (Th1I.2) Mark Filer and Sorin Tibuleac ADVA Optical Networking / Atlanta, GA mfiler@advaoptical.com N-degree ROADM Architecture Comparison: Broadcast-and-Select vs Route-and-Select in 120 Gb/s DP-QPSK Transmission Systems
- 2. © 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
- 3. © 2014 ADVA Optical Networking. All rights reserved.33 • 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
- 4. © 2014 ADVA Optical Networking. All rights reserved.44 to other degrees from other degrees route WSS select WSS 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
- 5. © 2014 ADVA Optical Networking. All rights reserved.55 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? 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-degree select WSS
- 6. © 2014 ADVA Optical Networking. All rights reserved.66 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 Recirculating loop emulating system with 24 cascaded ROADM nodes Experimental Configuration • 120 Gb/s DP-QPSK real-time coherent XPDR
- 7. © 2014 ADVA Optical Networking. All rights reserved.77 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 Recirculating loop emulating system with 24 cascaded ROADM nodes Experimental Configuration • 120 Gb/s DP-QPSK real-time coherent XPDR • ROADM nodes with: • EDFA + VOA, and • 1 N-degree WSS (B&S config), or • 2 N-degree WSSs (R&S config)
- 8. © 2014 ADVA Optical Networking. All rights reserved.88 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 Recirculating loop emulating system with 24 cascaded ROADM nodes Experimental Configuration • 120 Gb/s DP-QPSK real-time coherent XPDR • ROADM nodes with: • EDFA + VOA, and • 1 N-degree WSS (B&S config), or • 2 N-degree WSSs (R&S config) • 60-80km NZ-DSF, -6dBm/ch into fiber
- 9. © 2014 ADVA Optical Networking. All rights reserved.99 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 Recirculating loop emulating system with 24 cascaded ROADM nodes Experimental Configuration • 120 Gb/s DP-QPSK real-time coherent XPDR • ROADM nodes with: • EDFA + VOA, and • 1 N-degree WSS (B&S config), or • 2 N-degree WSSs (R&S config) • 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 mux 120G DP-QPSK xtalk
- 10. © 2014 ADVA Optical Networking. All rights reserved.1010 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 Recirculating loop emulating system with 24 cascaded ROADM nodes Experimental Configuration • 120 Gb/s DP-QPSK real-time coherent XPDR • ROADM nodes with: • EDFA + VOA, and • 1 N-degree WSS (B&S config), or • 2 N-degree WSSs (R&S config) • 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
- 11. © 2014 ADVA Optical Networking. All rights reserved.1111 • 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
- 12. © 2014 ADVA Optical Networking. All rights reserved.1212 • 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 Evolution R&SB&S 4x1 9x1 B&S R&S 4x1 9x1
- 13. © 2014 ADVA Optical Networking. All rights reserved.1313 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 4x1 9x1 B&S R&S 9x1 9x1
- 14. © 2014 ADVA Optical Networking. All rights reserved.1414 4x1 9x1 B&S R&S predicted from weighted crosstalk calculations 4x1 9x1 B&S R&S Cascaded Crosstalk Evolution
- 15. © 2014 ADVA Optical Networking. All rights reserved.1515 • 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&S B&S R&S B&S
- 16. © 2014 ADVA Optical Networking. All rights reserved.1616 • 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
- 17. OFC 2014, San Francisco CA (Th1I.2) mfiler@advaoptical.com Thank you. contact details: