Understanding DWDM and ROADM Networks - · PDF fileUnderstanding DWDM and ROADM Networks...
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To learn more, visit jdsu.com/fibertest Note: Specifications, terms, and conditions are subject to change without notice. 10143228 501 1007 DWDM.PO.FOP.TM.AE Understanding DWDM and ROADM Networks Crosstalk (XT) Four Wave Mixing (FWM) Crosstalk occurs in devices that filter and separate wavelengths. A pro- portion of optical power intended for a specific channel is found in an adjacent or different channel. Effects: generation of additional noise affecting optical signal to noise ratios (OSNR), leading to bit errors. Solutions: use appropriate optical channel spacing, for example 0.4 nm → 10 Gb/s. This interference phenomenon produces unwanted signals from three frequencies (f xyz = f x +f y -f z ) known as ghost channels. As three channels automatically induce a fourth, the term four wave mixing is used. FWM is problematic in systems using dispersion shifted fibers (DSF). Wave- lengths traveling at the same speed at a constant phase over long periods increase the effect of FWM. Effects: power transfer to new signal frequencies (harmonics), channel crosstalk and bit errors. Solutions: use of fibers with CD, irregular channel spacing. Chromatic Dispersion (CD) CD – the phenomenon of the different wavelengths of an optical pulse traveling at different velocities along a fiber and arriving at different times in the receiver. Effects: decrease of peak power, pulse broadening and bit errors. Solutions: use of fibers or modules with reverse CD values (DCF/DCM). Positive chromatic dispersion X Polarization Mode Dispersion (PMD) PMD – the effect of the different polarization modes (fast axis and slow axis) of a signal statistically traveling at different velocities due to fiber imperfections. Time difference is called Differential Group Delay (DGD). Effects: decrease of peak power distortion of pulse shape and bit errors. Solutions: careful fiber laying (no stress), use of new fiber with low PMD values, exact fiber geometry. DWDM signal Crosstalk λ 1 -λ 3 λ 1 λ 2 λ 3 DEMUX 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 fiber AWF All wave fiber O Original band C Conventional band E Extended band L Long band S Short band U Ultra long band CWDM ITU-T G.694.2: λ n = 1271 nm+n max. 18 channels DWDM ITU-T G.694.1: f n = f r ±n f r = 193.10 THz = 1552.12 nm C-band 196.0 - 191.5 THz (1529.54 - 1565.48 nm) L-band 191.5 - 184.5 THz (1565.48 - 1624.88 nm) Attenuation (dB/km) AWF SSMF 0.0 0.1 0.2 0.3 0.4 0.5 1200 1300 1400 1500 1600 1700 Wavelength (nm) 1260 1360 1460 1530 1565 1625 1675 O E S L U C 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/λ 2 } ∆λ NRZ Eye pattern Optical spectrum High CD Low CD High PMD Low PMD CD PMD Complexity/cost Distance 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. A modulation of the phase is used to increase transmission distance affecting complexity and cost of the system. The modulation techniques have direct impact on the optical spectrum and the eye pattern. NRZ Non Return to Zero RZ Return to Zero DB Duo Binary DPSK Differential Phase Shift Keying DQPSK Differential Quadrature Phase Shift Keying Understanding DWDM and ROADM Networks Optical Transport Networks Span Loss and Dispersion Management of a Link Tx Power DGD OSNR 0 OAM OAM OAM Raman Amplifier Rx Chromatic dispersion management is used to reduce FWM crosstalk in high speed long distance networks. Optical amplifiers with integrated dispersion compensators (OAM) are distributed along the link to recover the optical power and to overcome the positive dispersion of the fiber. Each amplifier will reduce the optical signal to noise ratio (OSNR) due to the ASE noise (amplified spontaneous emission noise). OSNR = Optical signal power Optical noise power Glossary ASE Amplified Spontaneous Emission of an optical amplifier CD Chromatic Dispersion CWDM Coarse Wavelength Division Multiplexing DCF Dispersion Compensation Fiber DCM Dispersion Compensation Module Demux Optical Demultiplexer DFB Distributed Feedback laser DGD Differential Group Delay DWDM Dense Wavelength Division Multiplexing EDFA Erbium Doped Fiber Amplifier FBG Fiber Bragg Grating FWM Four Wave Mixing MUX Optical Multiplexer OAM Optical Amplifier Module (incl. dispersion compensation) OSNR Optical Signal to Noise Ratio PLC Planar Lightwave Circuit PMD Polarization Mode Dispersion ROADM Reconfigurable Optical Add Drop Multiplexer WB Wavelength Blocker WSS Wavelength Selective Switch WXC Wavelength Cross Connect XT 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 Wavelength Blocker Combiner Splitter In Out Drop Add DEMUX MUX Add/Drop In Out DEMUX MUX λ 1 λ n In/ Add Out/ Drop 2 DWDM ports (1 In, 1 Out) Dynamic channel equalizer + wavelength blocking Long-haul, ultra long-haul Point to point → 2 degree ROADM Metro/Edge Lowest cost → 2 degree ROADM Metro/Edge Ring structure → ≥2 degree ROADM Not colorless Dynamic Thru & 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 interconnection Mesh 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) � �� Tx Tx Tx Tx λ 1 λ 2 λ 3 λ n MUX EDFA ROADM WXC Power spectrum of DFB-Tx ROADM ROADM ROADM WSS WSS OAM Module ROADM FBG EDFA Effect of ch Add/Drop with ROADM → needs in-band OSNR testing Raman Amplifier DEMUX λ 1 λ 2 λ 3 λ n Rx Rx Rx Rx Pump Drop Add PLC Effect of CD comp. with FBG filters Power spectrum of 27 ch system
Transcript of Understanding DWDM and ROADM Networks - · PDF fileUnderstanding DWDM and ROADM Networks...
To learn more, visit jdsu.com/fibertestNote: Specifications, terms, and conditions are subject to change without notice.10143228 501 1007 DWDM.PO.FOP.TM.AE
Understanding DWDM and ROADM NetworksCrosstalk (XT)
Four Wave Mixing (FWM)
Crosstalk occurs in devices that filter and separate wavelengths. A pro-portion of optical power intended for a specific channel is found in anadjacent or different channel.
Effects: generation of additionalnoise affecting optical signal tonoise ratios (OSNR), leading tobit errors.
Solutions: use appropriateoptical channel spacing, forexample 0.4 nm → 10 Gb/s.
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 fibers (DSF). Wave-lengths traveling at the same speed at a constant phase over long periods increase the effect of FWM.
Effects: power transfer to newsignal frequencies (harmonics),channel crosstalk and bit errors.
Solutions: use of fibers withCD, irregular channel spacing.
Chromatic Dispersion (CD)
CD – the phenomenon of the different wavelengths of an optical pulsetraveling at different velocities along a fiber and arriving at differenttimes in the receiver.
Effects: decrease of peak power,pulse broadening and bit errors.
Solutions: use of fibers ormodules with reverse CDvalues (DCF/DCM).
Positive chromatic dispersion X
Polarization Mode Dispersion (PMD)
PMD – the effect of the different polarization modes (fast axis and slowaxis) of a signal statistically traveling at different velocities due to fiberimperfections. Time difference is called Differential Group Delay (DGD).
Effects: decrease of peak powerdistortion of pulse shape andbit errors.
Solutions: careful fiber laying (no stress), use of newfiber with low PMD values,exact fiber 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 fiber AWF All wave fiber
O Original band C Conventional band E Extended band L Long band S Short band U Ultra long band
CWDM ITU-T G.694.2: λn = 1271 nm+n max. 18 channels
DWDM ITU-T G.694.1: fn = fr±n fr = 193.10 THz = 1552.12 nm
C-band 196.0 - 191.5 THz (1529.54 - 1565.48 nm) L-band 191.5 - 184.5 THz (1565.48 - 1624.88 nm)
Att
enu
atio
n (d
B/k
m)
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
Op
tica
l sp
ectr
um
High CD Low CD
High PMDLow PMD
CD
PMD
Co
mp
lexi
ty/c
ost
Dis
tan
ce
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.
A modulation of the phase is used to increase transmission distance affecting complexity and cost of the system.
The modulation techniques have direct impact on the optical spectrum and the eye pattern.
NRZ Non Return to ZeroRZ Return to ZeroDB Duo Binary
DPSK Differential Phase Shift KeyingDQPSK Differential 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 RamanAmplifier
RxChromatic dispersion management is used to reduce FWM crosstalk in high speed long distance networks. Optical amplifiers with integrated dispersion compensators (OAM) are distributed along the link to recover the optical power and to overcome the positive dispersion of the fiber. Each amplifier will reduce the optical signal to noise ratio (OSNR) due to the ASE noise (amplified spontaneous emission noise).
OSNR =Optical signal power
Optical noise power
Glossary
ASE Amplified Spontaneous Emission of an optical amplifierCD Chromatic DispersionCWDM Coarse Wavelength Division MultiplexingDCF Dispersion Compensation FiberDCM Dispersion Compensation ModuleDemux Optical DemultiplexerDFB Distributed Feedback laserDGD Differential Group DelayDWDM Dense Wavelength Division MultiplexingEDFA Erbium Doped Fiber AmplifierFBG Fiber Bragg GratingFWM Four Wave MixingMUX Optical MultiplexerOAM Optical Amplifier Module (incl. dispersion compensation)OSNR Optical Signal to Noise RatioPLC Planar Lightwave CircuitPMD Polarization Mode DispersionROADM Reconfigurable 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 & 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)
� � �Tx
Tx
Tx
Tx
λ1
λ2
λ3
λn
MU
X
EDFA
ROADM
WXC
Power spectrum of DFB-Tx
ROADM
ROADM ROADM
WSS
WSS
OAM ModuleROADM
FBG EDFA
Effect of ch Add/Drop with ROADM→ needs in-band OSNR testing
Raman Amplifier
DEM
UX
λ1
λ2
λ3
λn
Rx
Rx
Rx
Rx
Pump
Drop Add
PLC
Effect of CD comp. with FBG filters
Power spectrum of 27 ch system
