ROADM and DWDM
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Transcript of ROADM and DWDM
To learn more, visit jdsu.com/�bertestNote: Speci�cations, terms, and conditions are subject to change without notice.10143228 502 0811 DWDM.PO.FOP.TM.AE
Understanding DWDM and ROADM NetworksCrosstalk (XT)
Four Wave Mixing (FWM)
Crosstalk occurs in devices that �lter and separate wavelengths. A pro-portion of optical power intended for a speci�c channel is found in anadjacent or di�erent channel.
E�ects: generation of additionalnoise a�ecting optical signal tonoise ratios (OSNR), leading tobit errors.
Solutions: use appropriateoptical channel spacing, forexample 0.4 nm → 10 Gbps.
This interference phenomenon produces unwanted signals from threefrequencies (fxyz = fx + fy − fz) known as ghost channels. As three channelsautomatically induce a fourth, the term four wave mixing is used. FWMis problematic in systems using dispersion-shifted �bers (DSF). Wave-lengths traveling at the same speed at a constant phase over long periods increase the e�ect of FWM.
E�ects: power transfer to newsignal frequencies (harmonics),channel crosstalk, and bit errors.
Solutions: use of �berswith CD and irregular channelspacing.
Chromatic Dispersion (CD)
CD refers to the phenomenon when di�erent wavelengths of an optical pulse travel at di�erent velocities along a �ber and arrive at di�erenttimes in the receiver.
E�ects: decrease of peak power,pulse broadening, and bit errors.
Solutions: use of �bers ormodules with reverse CDvalues (DCF/DCM).
Positive chromatic dispersion X
Polarization Mode Dispersion (PMD)
PMD refers to the e�ect when di�erent polarization modes (fast axis and slow axis) of a signal statistically travel at di�erent velocities due to �berimperfections. The time di�erence is called Di�erential Group Delay (DGD).
E�ects: decrease of peak power,distortion of pulse shape, andbit errors.
Solutions: lay �ber carefully (no stress), use new �ber with low PMD values, exact �ber geometry.
DWDM signal
Crosstalk
λ1-λ3
λ1
λ2
λ3
DEM
UX
Original channels
Interference products
f113
f132
f223
f231
f312
f221
f223
f112
f321
f331
f231
f332
f
DGD
Slow
Fast
Optical Bands
40G Modulation Techniques
SSMF standard single-mode �ber AWF all wave �ber
O original band C conventional band E extended band L long band S short band U ultra long band
Att
enua
tion
(dB/
km)
AWF
SSMF
0.0
0.1
0.2
0.3
0.4
0.5
1200 1300 1400 1500 1600 1700
Wavelength (nm)
12601360
14601530
15651625
1675
O E S L UC
C-band 22 45 90 180 360
L-band 35 70 140 280 560
Maximum Number of Channels
Channel Spacing [GHz] 200 100 50 25 12.5
nm 1.6 0.8 0.4 0.2 0.1
Maximum Number of Channels (at 1550 nm)
GHz 200 100 50 25 12.5
δυ = {c/λ2} ∆λ
NRZ Eye pattern
Opt
ical
spe
ctru
m
High CD Low CD
High PMDLow PMD
CD
PMD
Com
plex
ity/c
ost
Dis
tanc
e
NRZ-DPSK RZ-DPSK
NRZ-DQPSK RZ-DQPSK
NRZ-DB
NRZ
NRZ
New modulation techniques are used in high- speed 40G networks to shift dispersion limitations.
NRZ formats are used to overcome large CD.
RZ formats are used to handle high PMD.
Phase modulation is used to increase transmission distances that a�ect the complexity and cost of the system.
Modulation techniques directly impact the optical spectrum and the eye pattern.
NRZ non-return-to-zeroRZ return-to-zeroDB duo-binary
DPSK di�erential phase shift keyingDQPSK di�erential quadrature phase shift keying
Understanding DWDM and ROADM Networks
Optical Transport Networks
Span Loss andDispersion Management of a Link
Tx
Power
DGD
OSNR
0
OAM OAM OAM RamanAmpli�er
RxManaging CD can reduce FWM crosstalk in long-distance high-speed networks. Optical ampli�ers with integrated dispersion compensators (OAM) are distributed along the link to recover the optical power and to overcome the positive dispersion of the �ber. Each ampli�er will reduce the OSNR due to the ASE noise.
OSNR = Optical signal power Optical noise power
Glossary
ASE ampli�ed spontaneous emission (noise) in an optical ampli�erCD chromatic dispersionCWDM coarse wavelength division multiplexingDCF dispersion compensation �berDCM dispersion compensation moduleDemux optical demultiplexerDFB distributed feedback laserDGD di�erential group delayDWDM dense wavelength division multiplexingEDFA erbium-doped �ber ampli�erFBG �ber Bragg gratingFWM four wave mixingMUX optical multiplexerOAM optical ampli�er module (incl. dispersion compensation)OSNR optical signal-to-noise ratioPLC planar lightwave circuitPMD polarization mode dispersionROADM recon�gurable optical add-drop multiplexerWB wavelength blockerWSS wavelength selective switchWXC wavelength cross-connectXT crosstalk
ROADM Types
Wavelength Blocker (WB) Small Switch Array (PLC) Wavelength Selective Switch (WSS) Wavelength Cross Connect (WXC)
Block Diagram
Ports
Network Function
Application
In Out WavelengthBlocker
Combiner Splitter
In Out
Drop Add
DEM
UX
MU
X
Add/Drop
In Out
DEM
UX
MU
X
λ1 λn
In/Add
Out/Drop
2 DWDM ports(1 In, 1 Out)
Dynamic channel equalizer+ wavelength blocking
Long-haul, ultra long-haulPoint to point→ 2 degree ROADM
Metro/EdgeLowest cost→ 2 degree ROADM
Metro/EdgeRing structure→ ≥2 degree ROADM
Not colorlessDynamic 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
Ring interconnectionMesh cross-connect→ ≥3 degree ROADM
2 DWDM ports + N single λ ports (1 In + 1 Out + N Add + N Drop)
N+1 DWDM ports (1 In + 1 Out + N-1 Add/Drop)
2N DWDM ports (N-1 In + N-1 Out + 1 Add + 1 Drop)
TxTxTx
Tx
λ1
λ2
λ3
λn
MU
X
EDFA
ROADM
WXC
Power spectrum of DFB-Tx
ROADM
ROADM ROADM
WSS
WSS
WSS
OAM ModuleROADM
FBG EDFA
E�ect of ch Add/Drop with ROADM→ needs in-band OSNR testing
Raman Ampli�er
DEM
UX
λ1
λ2
λ3
λn
RxRxRx
Rx
Pump
Drop Add
PLC
E�ect of CD comp. with FBG �lters
Power spectrum of 27 ch system
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