ROADM Network Design Issues

ROADM Network Design Issues March 23, 2009 NFOEC 2009, Tutorial

Sorin Tibuleac ADVA Optical Networking, Atlanta, GA [email protected]

Acknowledgments

Mark Filer, ADVA Optical Networking Sethumadhavan Chandrasekhar, Alcatel-Lucent Bell Labs Brandon Collings, JDSU Fred Heismann, JDSU Tom Strasser, Nistica Ross Saunders, Opnext Simon Poole, Finisar

2

Outline

Definition, features, benefits Node architecture ROADM Technologies and key optical parameters Transmission impairments Channel power control 100Gb transmission ROADM evolution

3

Definition ROADM = Reconfigurable Optical Add/Drop Multiplexer An optical subsystem capable of selective and automatic removal or addition of individual wavelengths from an optical fiber

ROADM

ROADM can also denote a network node 1x9 WSS

9:1 coupler

Transponders

4

Typical ROADM Features Typically associated with other features Switching with no impact on other wavelengths Wavelength monitoring (mostly power) Wavelength power equalization Network management SW for end-to-end automated provisioning Support for all data rates, modulation formats, protocols Supports external wavelengths 5

Benefits Demux

Mux

Transponders

ROADM

Transponders

Reduction of OpEx

Simpler network planning Simpler installation and turn-up of initial system Faster provisioning and turn-up of new channels Increased network availability - avoid manual operations

Reduction of CapEx Less OEO regeneration due to power equalization Optical switching with MD-ROADMs vs. OEO switching

Dynamic provisioning of services Mesh network protection options 6

ROADM Node Configurations

2-Deg. ROADM Node – Fixed λ per port “Degree” = Number of network interfaces

Transponders

iPLC implementation Built-in VOAs & OPM 100GHz/40λ

1:2 splitter

2x1 WSS

Lowest pass-through loss 100GHz/40λ and 50GHz/80λ Transponders 8

2-Deg. ROADM node - Colorless 1x9 WSS

9:1 coupler

Currently limited to 8 drop ports Transponders

Higher loss (mainly from coupler) Higher cost compared to 2x1 WSS

1x9 WSS

9:1 coupler

Expansion with additional Nx1 WSS’s

Transponders 9

Multi-degree ROADM Splitter Add/Drop

Network Interface 1 (Degree 1)

XPDR XPDR

WSS

10

XPDR XPDR


ROADM Scalability (deg-3) Splitter Add/Drop Network Interface 1 (Degree 1)

XPDR XPDR

WSS


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Add/Drop XPDR XPDR

XPDR XPDR


ROADM Scalability (deg-4) Splitter Add/Drop Network Interface 1 (Degree 1)

XPDR XPDR

WSS


XPDR XPDR

XPDR XPDR

XPDR XPDR

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Directionless Multi-Deg. ROADM Node Additional 9x1 WSS for directionless Fixed wavelength per transponder Tx/Rx ports Network Interface 1

Network Interface 2

1:N splitter

Nx1 WSS

Routing to/from any network interface

Transponders 13

Colorless and Directionless MD-ROADM Network Interface 2

Network Interface 1

1:N splitter

Nx1 WSS

Additional 1xN for colorless Wavelength blocking Non-blocking options using

Add/drop any λ on any tunable transponder

NxM WSS Optical cross-connect with filters, splitters, or 1xN WSS Transponders

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ROADM Module Technologies and Optical Performance

ROADM Technologies

2-degree MEMS – one axis for switching, other for attenuation Liquid crystals – stacked for Nx1 WSS Liquid crystal + 1-degree MEMS – MEMS attenuation, LC switching Liquid crystal on Silicon (LCOS) – multiple LC elements per λ Digital MEMS (DLP array) – multiple mirrors per λ Integrated planar lightwave circuits (iPLC) – silica or polymer Tunable filters (free-space optics, fiber gratings, PLC)

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Key Optical Parameters for WSS Multiple technologies and vendors, temperature variations & ageing Actual loss can be much lower BW Shape is important; det. by ratio of 3dB/0.5dB

3dB Bandwidth 0.5dB Bandwidth

5.5 - 7.0 dB 50 GHz

32-40

100 GHz

75-85

50 GHz

25-26

100 GHz

40-60

Determines crosstalk, BW is key

Extinction Ratio

35 – 40 dB

Required for power equalization

Attenuation

0 - 15 dB

PDL

0.3 – 1.5 dB

PMD

0.5 – 1 ps

Switch Time

~10ms – 1s

GDR

1-4 ps

Increases with attenuation Important for 40G/100G OPM, attenuation time & accuracy important 17

Loss

System Performance Implications

Transmission Impairments Insertion loss Metro networks Long-haul networks Polarization-dependent loss (PDL) Bandpass width, shape, ripple, and offset 10G locked lasers (metro core & long-haul) 10G unlocked lasers (metro-access) 40G Isolation and crosstalk Others Dispersion and dispersion map Phase ripple Dynamic crosstalk Power setting accuracy 19

ROADM Node Loss ROADM loss on express path includes WSS – across wavelengths, temperature, polarization Splitter/Coupler Power ripple from upstream fiber spans/network nodes Monitoring taps, ageing margin, equalization tolerances… 1x9 WSS

9:1 coupler

2 Deg. Colorless 1:9 splitter

Similar Loss

9x1 WSS

8 Deg. Colored 1:2 splitter 2x1 WSS

2 Deg. Colored 20

ROADM Loss in Long-Haul Networks ROADM node loss impact link distance for 20 and 25dB spans

ROADM

30 28

ROADM 12dB

26

ROADM 20dB

20dB Span

OSNR [dB]

24 22 20

25dB Span

18 16 14

OSNR threshold required by Receiver

12 10 0

2

4

6

8

10

12

14

16

Number of Spans 21

18

20

22

24

ROADM Loss in Metro Networks Span loss: 10dB

ROADM

Lower Loss = Lower cost by eliminating post-amp 30 28

ROADM 12dB - 1 amp

26

OSNR [dB]

24

ROADM 20dB - 2 amps

22 20 18 16 14 12 10 0

2

4

6

8

10

12

14

16

Number of Spans 22

18

20

22

24

Impact of ROADM PDL Power variations caused by PDL reduces transmission distance through reduction in OSNR, increase in nonlinear effects, and Rx noise or saturation 30.00

ROADM

PDL

28.00

0 ps 0.5 ps 1 ps

20dB Span

26.00

Assume ROADM node loss = 12 dB Increase in PDL 0.5 to 1.0dB = 3 spans

OSNR (dB)

24.00 22.00

PDL Impact

20.00 18.00

25dB Span

16.00 14.00 12.00 10.00 0

2

4

6

8

10

12

14

16

Number of Spans 23

18

20

22

24

Passband Narrowing and Ripple ROADM

Passband narrowing and accumulated ripple in recirculating loop with 80λ ROADMs Tx Individual passbands of 50GHz interleavers and 100GHz PLC ROADMs

Rx

Passband shape after 24 ROADMs (8 loops x3 ROADMs per loop 8x cascade of 6 interleavers (even) and 3 eROADMs

Individual passbands of all devices (even)

0 -2

-2

-4

-4

-6

-6

-10

PLC PLC ROADM ROADM

-8 IL [dB]

IL [dB]

-8

interleaver interleaver

-12 -14

-12 -14

-16

-16

-18

-18

-20 1530

-20 1530.5

1531 [nm]

24

-10

1531.5

1530

1530.5

1531 [nm]

1531.5

10G NRZ – 24 ROADMs 10G NRZ (locked) with PiN Rx and variable decision threshold No impact from passband narrowing and accumulated ripple in recirculating loop tests

Q_eff [dB] (measured)

17 With ROADMs Without ROADMs Back-to-back

16

15

14

13

12 1525

1530

1535

1540

1545

1550

Wavelength [nm] 25

1555

1560

1565

4.0

OSNR Penalty [dB]

2.0

Locked

Unlocked 2.5

16 ROADMs 12 ROADMs 8 ROADMs 4 ROADMs

0

-6

-20 ROADM 1

-7

-40

ROADM 2

-8

-60

ROADM 3

-9

[ps/nm]

-5

[ps/nm]

20

-80

ROADM 4

-100 -0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Wider, higher-order Gaussian shaped passband required for unlocked lasers

0.5 0.0 0.00

Wavelength [nm]

26

40

-4

Penalties enhanced by propagation through same devices in recirculating loop

1.0

-0.05

60

-3

[nm]

1.5

-0.10

80

-2

-10 -0.4

3.5 3.0

100

Dispersion

Wavelength drift of unlocked lasers can generate higher penalties

Transmittance [dB]

10G unlocked lasers used in metro/access

0 -1

[dB]

Wavelength Drift and Passband Effects

0.05

0.10

Tunable-filter ROADMs