Download - Introduction to Dwdm Technology
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Introduction to DWDM Technology
James Tai
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•General Background
•Why DWDM?
•Fundamentals of DWDM Technology
•Future Trend
Outline
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General Background
Year
Optical TransmissionDoubling every 9 Months
Data StorageDoubling every 12 Months
Silicon Processing (Moore’s Law)Doubling every 18 Months
•Bandwidth Explosion
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Why DWDM?
•High Bandwidth Demand:- Bandwidth are doubling every 3 months - Internet traffic increases thousand-fold every 3 years
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How to increase Bandwidth
•SONET& TDM: Increase the bit rate by using high speed electronics
OC-12 OC-48 OC-192 OC-768
622 Mb/s 2.5 Gb/s 10 Gb/s 40 Gb/s
Note: For signal rate <10 Gbps, the cost per bit will drop approximately
40% when the bit rate increases fourfold.
•FDM: Increase the radio frequency channel (BW)
•WDM: Increase the capacity of a single fiber by using a technology of
combining and separating optical signals of different wavelengths
sent along an optical fiber
- e.g. Multiplex multiple TDM signals of OC-N over a single fiber
(multiple OC-N signals each over a single fiber X N fibers)
= NX(OC-N) signal over a single fiber
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What is WDM ?
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Evolution of WDM
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TDM vs WDM
Carry multiple protocols (protocol independent)
Carry synchronous TDM hierarchy
No O-to-E conversion before signals being multiplexed/demuxed
Optical-to-electrical (O-to-E) conversion before signals being multiplexed/demuxed
Optically multiplex individual wavelengths over a single fiber
Electronically multiplex signals to a single higher bit rate at a single wavelength for transmission
WDM (DWDM)SONET TDM
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WDM v.s. DWDM
•DWDM spaces the wavelengths more closely than does WDM,
and therefore has a greater overall capacity
•State-of-the-art technology: 273 wavelengths, 40Gbps/wavelength
10.9Tbps over single fiber (NEC, Mar2001)
this capacity means (1) 1,560M of DS0 or
(2) 167M of MPEG-2 or
(3) 2.5K of CD-ROM (500MB/CD-ROM)
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Fundamentals of DWDM Technology
1. Optical Fiber
2. Optical Light Source and Detector
3. Optical Amplifier
4. DWDM Multiplexer and Demultiplexer
5. Optical Switch (Optical Cross-Connect)
6. Optical Add/Drop Multiplexer
7. Wavelength Router
8. Optical DWDM Transponder
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• Fiber cable: core /cladding layer diameter
Multi-mode fiber (MMF): 50/125 or 62.5/125 µm
Single-mode fiber (SMF): 9/125 µm
SMF core
MMF core
Cladding layerLight path
Optical Fibers
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Fiber Attenuation & DWDM Operating Bandwidth
Note:DWDM BW
(1) S-band: 1485~ 1520 nm
(2) C-band:1530 ~ 1562 nm
(3) L-band: 1570 ~1610 nm
“S”
ban
d
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Transmission Problems in Optical Fibers
•Linear Effects: can be compensated
(1) Attenuation
(2) Dispersion
•Non-Linear Effects: will accumulate (not so critical in short-haul network)
(1) Polarization Mode Dispersion (not a problem at speeds < OC-192)
(2) Stimulated Brillouin Scattering
(3) Stimulated Raman Scattering
(4) Self-Phase Modulation
(5) Four-Wave Mixing
(the most critical effect; will limit the channel capacity of DWDM system)
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Dispersion
Output
Concept of Dispersion
Horse Race
Input
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Dispersion
17 ps/(Km*nm) -100 ps/(Km*nm)
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Optical Channels (Optical Frequency, nm)
Pow
er
Optical Fiber
Flat InputTilt Output (After SRS)
Stimulated Raman Scattering
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Four-Wave Mixing
Optical Carriers (@ 50/100GHz Spacings)
f1 f2 f3 f4 Frequency
Four Wave Mixing creates
cross-talk for channel f1
Channels f1, f2, f3 interact to
create a intermodulation product
(sideband) at (f1+f2+f3)
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• Fiber cable attenuation: Depend on core size and operating wavelength
MMF SMF
Core Diamater(µm)
Wavelength(nm)
Loss (dB/Km)
Dispersionps/(nm x Km)
50 62.5 9
1310 1550
0.35 0.22
171
2.7 3.2
850 1300 850 1300
0.8 0.9
BW (MHz) xLength (Km) 400 1000 200 500
Optical Fibers
New Fiber: 10GbpsX40m
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•Limitation on System Performance Using MMF
(1) Insufficient bandwidth and transmission distance
(2) Higher loss than SMF’s
(3) Interference induced modal noise → SNR degradation
Optical Fibers
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Optical Fibers
•Three MajorTypes of Single Mode Fiber (SMF):
(1) Non-dispersion-shifted fiber (NDSF), G.652 (standard SMF)
(a) >95% of deployed plant; has serious fiber dispersion problem
(b) suitable for TDM use in single channel 1310 nm or DWDM use in
1550 nm window (with dispersion compensators)
(2) Dispersion-shifted fiber (DSF), G.653
(a) exhibits serious fiber nonlinearity problem, i.e. FWM
(b) Suitable for TDM use in the 1550 nm window, but not suitable for DWDM
(3) Non-zero dispersion-shifted fiber (NZ-DSF), G.655
(meet the needs of DWDM applications)
As bit rates approach to 10 Gb/s and beyond, the interdependence between system and fiber design will be very important for system planning
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Chromatic Dispersion
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Optical Light Sources and Detectors• Light Source:
(a) Light Emitting Diode (LED)
(b) Laser Diode (LD): VCSEL, Fabry-Perot (FP) Laser, Distributed Feedback Laser (DFB)
BW
Noise
Linearity
Environmental Influence
LED FP DFB
WideNarrow
Application Digital,<1 Gbps
Digital &Analog
LowHigh
Poor
Unstable
Good
~
~
~
~
DWDM Digital (10Gb/s) &
Analog
Stable
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• L-I Response of Light Source:
(a) LED (b) Laser Diode
Opt
ical
Pow
er (
mW
)
Bias (mA)
Distorted Signals
AC Signal
Modulated Optical Signals
AC Signal
Optical Light Sources and Detectors
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Comparison of Key Performance Features for VCSEL, DFB, and FP lasers
VCSEL DFB Fabry Perot Emission Type Surface Edge Edge Emission Pattern Circular Elliptical Elliptical Divergence Angle ~ 10 degree ~ 30 degree ~ 30 degree Spectral Width 0.1 nm 0.1 nm 2 ~ 5 nm Peak Modulation Speed 20 Gb/s ~ 10 Gb/s ~ 10 Gb/s Threshold Current 1 ~ 5 mA 10 ~ 15 mA 2 ~ 5 mA Fiber Coupling Efficiency 80% 10% 10% Coupling Optics Not required Aspheric lens Aspheric lens Wavelength Drift ~0.1 nm/deg C ~0.1 nm/deg C ~0.5 nm/deg C Link Distance for 10 GbE Transponder
VSR (850 nm, 300m of new MM fiber)
IR (1310 nm, 2~12Km)
IR (Direct Modulation)
IR
Power Consumption for 10 GbE Transponder
3W ~ 4W 7W ~ 10W 7W ~ 10W
Rel. Price of packaged Laser @ 1Gb/s
1X 25X 4.5X
(Source: 2001, Mar. issue of Fiber Optic Product News)
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Direct Modulation v.s. External Modulation
•Direct Modulation: Chirp can become a limiting factor at high bit rates (> 10 Gb/s)
•External Modulation: help to limit chirp
DFBOptical Output (SMF)RF Input
RF InputVRF
Bias ControlVBIAS
3 dB -Coupler
Phase Modulator
PM fiberin
SMF fiberoutDFB
λ @ ITU -grid
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ITU Defined Wavelengths (100GHz = 0.8 nm)
C h a n n e l N u m b e r
W a v e l e n g t h ( n m )
F r e q u e n c y ( G H z )
C h a n n e l N u m b e r
W a v e l e n g t h ( n m )
F r e q u e n c y ( G H z )
1 5 1 5 6 5 . 4 9 6 1 1 9 1 , 5 0 0 4 4 1 5 4 2 . 1 4 2 5 1 9 4 , 4 0 0
1 6 1 5 6 4 . 6 7 9 0 1 9 1 , 6 0 0 4 5 1 5 4 1 . 3 4 9 6 1 9 4 , 5 0 0
1 7 1 5 6 3 . 8 6 2 8 1 9 1 , 7 0 0 4 6 1 5 4 0 . 5 5 7 6 1 9 4 , 6 0 0
1 8 1 5 6 3 . 0 4 7 5 1 9 1 , 8 0 0 4 7 1 5 3 9 . 7 6 6 3 1 9 4 , 7 0 0
1 9 1 5 6 2 . 2 3 2 9 1 9 1 , 9 0 0 4 8 1 5 3 8 . 9 7 5 9 1 9 4 , 8 0 0
2 0 1 5 6 1 . 4 1 9 3 1 9 2 , 0 0 0 4 9 1 5 3 8 . 1 8 6 3 1 9 4 , 9 0 0
2 1 1 5 6 0 . 6 0 6 5 1 9 2 , 1 0 0 5 0 1 5 3 7 . 3 9 7 4 1 9 5 , 0 0 0
2 2 1 5 5 9 . 7 9 4 5 1 9 2 , 2 0 0 5 1 1 5 3 6 . 6 0 9 4 1 9 5 , 1 0 0
2 3 1 5 5 8 . 9 8 3 4 1 9 2 , 3 0 0 5 2 1 5 3 5 . 8 2 2 2 1 9 5 , 2 0 0
2 4 1 5 5 8 . 1 7 3 1 1 9 2 , 4 0 0 5 3 1 5 3 5 . 0 3 5 8 1 9 5 , 3 0 0
2 5 1 5 5 7 . 3 6 3 6 1 9 2 , 5 0 0 5 4 1 5 3 4 . 2 5 0 3 1 9 5 , 4 0 0
2 6 1 5 5 6 . 5 5 5 0 1 9 2 , 6 0 0 5 5 1 5 3 3 . 4 6 5 5 1 9 5 , 5 0 0
2 7 1 5 5 5 . 7 4 7 3 1 9 2 , 7 0 0 5 6 1 5 3 2 . 6 8 1 5 1 9 5 , 6 0 0
2 8 1 5 5 4 . 9 4 0 4 1 9 2 , 8 0 0 5 7 1 5 3 1 . 8 9 8 3 1 9 5 , 7 0 0
2 9 1 5 5 4 . 1 3 4 3 1 9 2 , 9 0 0 5 8 1 5 3 1 . 1 1 5 9 1 9 5 , 8 0 0
3 0 1 5 5 3 . 3 2 9 0 1 9 3 , 0 0 0 5 9 1 5 3 0 . 3 3 4 4 1 9 5 , 9 0 0
3 1 1 5 5 2 . 5 2 4 6 1 9 3 , 1 0 0 6 0 1 5 2 9 . 5 5 3 6 1 9 6 , 0 0 0
3 2 1 5 5 1 . 7 2 1 0 1 9 3 , 2 0 0 6 1 1 5 2 8 . 7 7 3 6 1 9 6 , 1 0 0
3 3 1 5 5 0 . 9 1 8 3 1 9 3 , 3 0 0 6 2 1 5 2 7 . 9 9 4 4 1 9 6 , 2 0 0
3 4 1 5 5 0 . 1 1 6 3 1 9 3 , 4 0 0 6 3 1 5 2 7 . 2 1 6 0 1 9 6 , 3 0 0
3 5 1 5 4 9 . 3 1 5 3 1 9 3 , 5 0 0 6 4 1 5 2 6 . 4 3 8 4 1 9 6 , 4 0 0
3 6 1 5 4 8 . 5 1 5 0 1 9 3 , 6 0 0 6 5 1 5 2 5 . 6 6 1 6 1 9 6 , 5 0 0
3 7 1 5 4 7 . 7 1 5 5 1 9 3 , 7 0 0 6 6 1 5 2 4 . 8 8 5 6 1 9 6 , 6 0 0
3 8 1 5 4 6 . 9 1 6 9 1 9 3 , 8 0 0 6 7 1 5 2 4 . 1 1 0 3 1 9 6 , 7 0 0
3 9 1 5 4 6 . 1 1 9 1 1 9 3 , 9 0 0 6 8 1 5 2 3 . 3 3 5 9 1 9 6 , 8 0 0
4 0 1 5 4 5 . 3 2 2 2 1 9 4 , 0 0 0 6 9 1 5 2 2 . 5 6 2 2 1 9 6 , 9 0 0
4 1 1 5 4 4 . 5 2 6 0 1 9 4 , 1 0 0 7 0 1 5 2 1 . 7 8 9 3 1 9 7 , 0 0 0
4 2 1 5 4 3 . 7 3 0 7 1 9 4 , 2 0 0 7 1 1 5 2 1 . 0 2 0 0 1 9 7 , 1 0 0
4 3 1 5 4 2 . 9 3 6 2 1 9 4 , 3 0 0 7 2 1 5 2 0 . 2 5 0 0 1 9 7 , 2 0 0
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•Optical channel numbers can be increased by spacing the wavelengths more
closely, at 50 GHz, to double the number of channels.
However, spacing at 50 GHz limits the maximum data rate per λ to 10 Gb/s
•The closer the wavelength spacings, the more optical channel crosstalk results
•Nonlinear interactions among different DWDM channels creates intermodulation
products (FWM) that can induce interchannel interference, resulting in crosstalk
and SNR degradation.
The closer the spacings, the more FWM interference results
ITU-Grid (ITU-G.692) Wavelengths
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Op
tica
l Lin
e R
ate
Distance (Km)1 10 100
0.01
0.1
1
10
100
Short Reach Intermediate Reach
Short Reach1300 nm
Long Reach1550 nm
VCSEL
Optical Transceiver Evolution (using SMF)
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Si Ge InGaAs
Spectral Response for Photodiode
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Optical Receiver Design Issue
p
n
i
p-InGaAs or
p-InP
n-InGaAs
n-InP
CONTACT METALIZATION
hν
RL
V
carrier drift
electrondiffusion
holediffusionSUBSTRATE
DEPLETIONLAYERWd
Tuning + Matching
CircuitPhoto-diode
To 50 Ohm Load
- Two Important Design Issues for “impedance matched receiver”:
(1) Low Noise
(2) Wide Bandwidth
•PIN Photodiode:
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PIN Photodiode Avalanche Photodiode (APD)
Photon-Electron Conversion
1:1 1:N (N=10)
Receiver Sensitivity Medium High Cost Low High Reliability High Moderate Temperature Sensitivity Low High
Photodiode
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Optical Amplifiers- DWDM Enabler -
Tx Repeater Rx
3R Functions: - Retiming- Reshaping- Retransmission
TxOptical
Amplifier Rx
(1) Conventional Design
(2) New Design (can save 60 to 80% regenerator costs)
1R Function: -Retransmission orReamplification
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Optical Amplifiers
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DWDM Bandwidth
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Optical Amplifiers
•Optical Fiber Amplifier- Pr-Doped Fiber Amplifier (PDFA; 1310nm region)- Th-Doped Fiber Amplifier (TDFA; S Band in 1500 nm region, 20 dB gain, 35 nm gain BW)
- Er-Doped Fiber Amplifier (EDFA; C or L Band in1550nm region, 30~ 40 dB gain)
•EDWA: Er-Doped Waveguide Amplifier (14dB gain)
•Semiconductor Optical Amplifier (SOA)- can operate in 1310 nm or 1550 nm region, 30 nm gain BW- not suitable for DWDM transmission
•Raman Amplifier - can provide gain from 1300 to 1550 nm or wider, 20 dB gain
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•Single Channel EDFA
•DWDM EDFA
Erbium-Doped Fiber Amplifier
Gain Flattening Filter
980-nm pumps 1480-nm pumps
EDF, pre-amp stage EDF, booster stage
DispersionCompensation Unit
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EDFA Flattened Gain Response
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Erbium-Doped Waveguide Amplifier
Gain @3~5dB/cm;Total length: 5~ 10 cm
Note: Pump Mux, Tap Coupler, and Mode Adapter can be integrated on to a single chip. (Drawback: absence of integrated isolators)
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Performance Comparison among Optical Amplifiers
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(A) Discrete Raman Amplifier
(using specialty fiber)
(B) Distributed (Lumped) Raman Amplifier
(using transmission fiber)
- pump @ 1450 nm,
- remote & back inject into 100Km fiber
- distributed gain over 40 Km
- pumping efficiency ~ 1/5* EDFA’s
Optical Raman Amplifier
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Why use Raman Amplifier?
• Improve system signal-to-noise ratio (SNR)
•Permit higher-speed (40Gbps) transmission by reducing
fiber nonlinearity
• Extend repeater span
• Raman gain from 1300 to 1500 nm or wider
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•80 Km for each span•DWDM terminal spacing ~ 400~600 Km (followed by a regenerator)
DWDM Transmission Span
•Concerned Factors:
(1) Fiber type
(2) Transmission distance
(3) Channel count and bit rate
DW
DM
DW
DM
80 Km (span)
Cascaded Optical Amplifiers
400 ~ 600Km (link)
(4) Amplifier spacing
(5) Amplifier noise
(6) Amplifier power
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DWDM Multiplexer/Demultiplexer
Technologies include:
•Thin film coating filters
•Fiber Bragg gratings
•Diffraction gratings
•Arrayed waveguide gratings
•Fused biconic tapered devices
• Inter-leaver devices
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Channel Spacing
Crosstalk
FilterBandwidth
Device Aspects of WDM Filter
- Figure of merit, -0.5 dB bandwidth/ -30 dB bandwidth
- Low loss
- Low Polarization sensitivity
- Flat top
- Steep roll-off
- Stable & Manufacturable
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DWDM Multiplexer/Demultiplexer Advantages Disadvantages Thin Film Coating Filters (1) Flexible in channel count and
irregular wavelength plan (2) Totally passive/temperature stable (3) Good optical performance in
isolation, insertion loss, PDL, and PMD
(4) wideband application (up to 16 Chs)
(1) Takes longer time to develop and accumulate filters with dense channel spacing
(2) Cost is proportional to channel count
Fiber Bragg Gratings (1) Excellent filter shape (2) Good optical performance in
isolation, insertion loss(when used as a notch filter)
(3) Short development time (4) Fused coupler + FBG, achieve 50
GHz spacing
(1) Not suitable for wideband applications
(2) Need temperature stabilization (3) Cost is proportional to channel
count
Arrayed Waveguide Gratings (1) Cost is not proportional to channel Count (cost effective for DWDM )
(2) Short development time to dense channel spacings
(5) Relative low insertion loss for high channel count
(6) Compact size (7) Potential to integrate with other
functions
(1) Poor filter shape (2) High nonadjacent channel
noise (3) Need temperature stabilization (4) High PDL and PMD
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DWDM Multiplexer/Demultiplexer
Interleaver
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Optical Switch
•MEMS(micro-electromechnical system)-Based Photonic Switch:
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Performance for 1X2/2X2 MEMS-Based Latching Optical Switch (using 2-D MEMS)
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•2-D Design MEMS
•3-D Design
MEMS Crossconnects
Plan 2
Plan 1 Plan 1 Plan 1
Plan 2 Plan 2 Plan 2
Plan 3 Plan 3
Plan 4
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Optical Add/Drop Multiplexer
•Current OADM (Add/Drop fixed wavelengths)
•Emerging OADM (Add/Drop any selection of wavelengths)
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Characteristics of Optical Add/Drop Multiplexer
•Has one or more optical fiber inputs and corresponding outputs, with multiple wavelengths multiplexed on each fiber
•Demultiplexes some or all of the wavelengths on the coming fiber and drops these wavelengths, one wavelength per fiber, to subscribers and directly or via electronicdemultiplexing to lower data rates
•Add signals from subscribers, one wavelength per fiber, multiplexes theseon outgoing fiber
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Optical Add/Drop Multiplexer
• Current Throughput: 8 ~ 16 X 2.5 Gb/s = 20 ~ 40 Gb/s
R: ReceiverT: Transmitter @ fixed λ
DW
DMλ1 ~ λ8
Optical Amplifier
DW
DM
R R
Fiber to Subscriber
TT
Fiber from Subscriber
Electronic Add/Drop
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Optical Add/Drop Multiplexer
•Estimated Throughput in 2008: 128 X10Gb/s = 1.28 Tb/s
DW
DMλ1 ~ λ128
Optical Amplifier
Optical Crossconnect
(128X256)
DW
DM
R R
Fiber to Subscriber
TT
Fiber from Subscriber
Electronic Add/Drop
R: ReceiverT: Tunable Transmitter
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Wavelength Router (Dynamic WDM Crossconnect)
Tunable laser inside(1) Tuning speed < 2 ns, (2) Tuning throughout the C-band <15ns(3) Synchronization time < 40 ns
(Source: 2001, Mar issue of Lightwave)
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Optical Transponder / Wavelength Adapter
λ @850/1310/1550nm)
DWDM Optical Transponder
DW
DM
(1) Embeded DWDM Operation (2) Open DWDM Operation
Optical Transponder
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Operation of DWDM-Based System
DW
DM
DW
DM
Pre-
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Optical Bandwidth
Channel Spacing Channel Bit Rate Fiber Bandwidth
Current benchmark 50 GHz 10 Gb/s @ 50GHz spacing C band
State-of-the-art technology 25 GHz 40Gb/s @ 100GHz spacing S and L band
Improvement gain X2 X2 X3
Challenge (1) Laser stabilization (2) Mux/DeMux tolerance (3) Filter technology (4) Fiber nonlinear effects
(1) PMD mitigation (2) Dispersion
compensation (3) High speed SONET
Mux/DeMux
(1) Optical Amplifier (2) Band Splitters &
Combiners (3) Gain tilt due to
stimulated Raman scattering
•Optical bandwidth can be increased by increased by improving DWDM system in three areas:
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Current Networking Status
DWDM Terminal
Migrating the SONET Ring to DWDM
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Optical Transport
SONET / SDH
ATM
IP / MPLS
Current IP / ATM / SONETLayering
SONET / SDH
IP / MPLS
IP / MPLS
Packet-over-SONETLayering
Direct IP-over-DWDMLayering
Time
Future Trend
Eliminating Protocol layers
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Key requirements in the MAN for DWDM systems
•Multiprotocol support
•Scalability
•Reliability and availability
•Openness (interface, network management, stand fiber types,
electromagnetic compatibility)
•Ease of installation and management
•Size and power consumption
•Cost effectiveness
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Metropolitan Area Networks
•Metro Core
•Metro Access
•Enterprise
Metro DWDM Systems
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Optical Networking Applications in MAN