ROADM and DWDM

Understanding DWDM and ROADM Networks Networks Optical Bands

PowerspectrumofDFB-Tx

Crosstalk (XT)

Optical Transport Networks

λ1

0.5

   0    2  6    1

   0    3  6    1

   0   4  6    1

   0    5    3    5    5  6    1    1

   5    2   6    1

   5    7   6    1

0.4

λ1-λ3 Crosstalk      X     U     M     E     D

DWDMsignal

WSS

λ2

λ1 λ2

 Tx λ3

 Tx

Crosstalk occurs in devices that lter and separatewavelengths. A proportion of optical power intended for a specic channel is found in an adjacent or dierent channel. Eects: generation ofadditional noiseaecting optical signalto noiseratios(OSNR),leadingto bit errors.

ROADM

ROADM

WXC

    X     U     M

Solutions: useappropriate optical channel spacing,for example0.4nm → 10Gbps.

EDFA

    3     1     1     f

    2     3     1     f

    2     3     3     f     1     3     2     f

    3     2     2     f     3     2     2     f

    2     1     3     f

    1     2     2     f

    1     2     3     f

Raman Amplier

WSS

ROADM

OAM Module FBG

Original channels

    2     1     1     f     1     3     2     f

λ1 λ2

ROADM

λ3

λn

 Tx

Four Wave Mixing (FWM)

WSS

ROADM

λ3

 Tx

    )    m     k     /     B     d     (    n    o     i    t    a    u    n    e    t    t     A

Eectof ch Add/Dropwith ROADM → needsin-band OSNRtesting

PLC

    X     U     M     E     D

Rx

0.1

Rx Rx

0.0

E

1300

S

1400

C

1500

SSMF standard single-modeber O original band E extended band S short band

L

U

1600

1700

AWF all waveber

C conventional band L longband U ultra longband

Rx

Interferenceproducts

Powerspectrumof27 chsystem

    1     3     3     f

D ro ro p A dd MaximumNumberof Channels

f 

Solutions: useofbers with CDand irregular channel spacing.

Glossary Eectof CD comp.with FBGlters

Span Loss and Dispersion Management of a Link   Tx

Chromatic Dispersion (CD)

OAM

OAM

Rx

Raman Amplier

OAM

Power

ManagingCD can reduceFWM crosstalk inlong-distance high-speed networks.Optical ampliers with integrated dispersion compensators (OAM) aredistributed along the link to recover theoptical power and to overcome the positivedispersion ofthe ber.Each amplier will reduce theOSNR dueto theASE noise.

DGD 0

X Positivechromatic dispersion

OSNR =

CDrefers to the phenomenon when dierent wavelengths ofan optical pulsetravel at dierent velocities alonga ber and arriveat dierent times in thereceiver. Eects: decreaseof peak power, pulsebroadening, and bit errors.

O 1200

Pump

 This interferencephenomenon produces unwanted signals from three frequencies (f xyz xyz = f x + f y − f z) known as ghost channels.As threechannels automatically inducea fourth,th eterm four wavemixing is used.FWM is problematic in systems usingdispersion-shifted bers (DSF). Wavelengths travelingat the samespeed at a constantphaseover long periods increasethe eect ofFWM. Eects: power transfer to new signal frequencies (harmonics), channel crosstalk,and bit errors.

AWF 0.2

Wavelength (nm)

λn

EDFA

SSMF 0.3

Solutions: useofbers or modules with reverseCD values (DCF/DCM).

Optical signal power Optical noisepower

OSNR

ASE CD CWDM DCF DCM Demux DFB D GD GD DWDM EDFA FBG F WM MUX OAM OSNR P LC PMD ROADM WB WSS WXC WX C XT

amplied i ed spontaneous emission(noise) in an optical amplier i er c hr hr om om at ic d is is pe pe rs rs io n coarsewavelengthdivision multiplexing dispersion compensation ber disper persio sion n compen compensat sation module optical demultiplexer distributedfeedback las laser er d i er er en en titi al al g r o up d e la y densewavelength division multiplexing erbium-doped ber amplier ber Bragggrating f ou r wa wa ve m ix in in g optical multiplexer optical ampliermodule(incl.dispers e (incl.dispersion compensation) optical signal-to-noiseratio p la na na r li g ht wa wa ve ve c i rc rc ui ui t polari a rizat z ation modedisp edispers ersion ion recongurableoptical e opticaladd-dropmultiplexer p lexer w av el el en en gt gt h b lo ck ck er er wavelength selectiveswitch wavele elength ngthcro crossss-connect c onnect crosstalk 

Channel Spacing[GHz]

20 0

1 00

50

25

12.5

C-band

22

45

90

1 80

360

L-band

35

70

140

28 0

560

MaximumNumberof Channels(at1550 nm) GHz

20 0

1 00

50

25

12.5

nm

1.6

0.8

0.4

0.2

0.1

40G Modulation Techniques CD

High CD

RZ-DPSK 

RZ-DQPSK 

NRZ-DQPSK     e    c    n    a    t    s     i     D

   t    s    o    c     /    y    t     i    x    e     l    p    m    o     C

NRZ-DB NRZ

NRZ

Smal l Sw Switch Ar Array (P (PLC)

Wavelength Blocker(WB)

Wavelength Se Selective Sw Switch (W (WSS)

Wavelength Cr Cross Co Connec t (W (WXC) Low PMD

Block Diagram

In

Wavelength Blocker

Splitter

Out

Combiner

In

Out

    X     U     M     E     D

In

    X     U     M

    X     U     M

N RZ

In/ Add

Drop

Fast

λ1

Ad d

λn Add/Drop

Ports

2DWDMports (1In,1Out)

2DWDMports + Nsingleλports (1In + 1 Out + NAdd + NDrop)

N+1DWDMports (1In + 1Out + N-1Add/Drop)

2NDWDMports (N-1In + N-1Out + 1 Add + 1Drop)

PMDrefers to the eect when dierent polarization modes (fast axis and slow axis) ofa signal statistically travel at dierent velocities dueto ber imperfections.Thetime dierenceiscalled DierentialGroupDelay (DGD).

Network Function

Dynamic channel equalizer + wavelength blocking

Not colorless Dynamic Thru and Add channel balancing

Colorless → switches λs from In to Out/Drop and Add to Out

Colorless → switches λs from In or Add to Out or Drop

Eects: decreaseof peak power, distortion ofpulse shape,and bit errors.

Application

Long-haul,ultra long-haul Point to point → 2degreeROADM

Metro/Edge Lowest cost → 2degreeROADM

Metro/Edge Ringstructure → ≥2degreeROADM

Ring interconnection Mesh cross-connect → ≥3degreeROADM

To learn more, visit jdsu.com/bertest

PMD

High PMD

Out

    X     U     M     E     D

Slow

Solutions: lay ber carefully (no stress),use new ber with low PMDvalues,exact ber geometry.

Lo w CD

NRZ-DPSK 

ROADM Types

Polarization Mode Dispersion (PMD) DGD

δυ= {c/λ 2} ∆λ

Out/ Drop

E ye p at e t rn

   m    u    r    t    c    e    p    s     l    a    c     i    t    p     O

New modulation techniques areused in highspeed 40G networks to shift dispersion limitations. NRZ formats areused to overcomelargeCD. RZ formats areused to handleh igh PMD.

Phasemodulation is used to increase transmission distances thataect thecomplexity and cost ofthe system. Modulationtechn a tiontechniquesdirectlyimpacttheopticalspectrumandtheeyepattern. NRZ RZ DB

non-return-to-zero return-to-zero du oo- bi na nar y

DPSK dierential phaseshift keying DQPSK dierential quadraturephase shift keying

Understanding DWDM and ROADM Networks

 n g  t i i n  c T e s t  O p t i c T  r O  b e r  F i b  2  e 2  e  V o l u m

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