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Transmission Network Development
Advanced Technology Laboratories
DWDM Transmission Technology and Photonic Layer Network
Chao-Xiang Shi
SprintSprintTransmission Network Development Group
Advanced Technology Laboratories1 Adrian , Burlingame
CA 94010
Transmission Network Development
Advanced Technology Laboratories
DWDM Technology in terrestrial network
- DWDM capacity and transmission distance: technology review
- DWDM transmission system
- Span design in DWDM transmission
- Optical transmitter in DWDM system: DFB laser with
external modulator
- Wavelength multiplex/de-multiplex technology in DWDM:
AWG, Dielectric filter, and Fiber grating type
- Two-stage optical fiber amplifier
- Optical amplification, bandwidth , and capacity
- Optical fiber nonlinearity: SPM, XPM, SBS, and FWM
- Polarization mode dispersion (PMD) limitation for 10 Gbit/s
and beyond
Outline
Transmission Network Development
Advanced Technology Laboratories
- PMD compensation technology
•DWDM technology in Submarine network - capacity and transmission distance : technology review - uniquely designed LCF fiber and non-zero dispersion shift fiber - chromatic dispersion compensation in Submarine transmission - PMD concern in submarine transmission - one stage Er. Doped fiber amplifier - comparison of WDM transmission between terrestrial and submarine network
• Photonic layer network - Optical network architecture - Protection and restoration mechanism for IP/ATM directly over WDM optical network
Continue
Transmission Network Development
Advanced Technology Laboratories
- Issues of protocols and interfaces requirements for all-optical networks - Key issue in Metro WDM network and possible solutions - Application of Metro WDM equipment in transparent
transport network: Experimental Verification• Emerging Technology of Optical Network
- Optical CDM (CDMA)- Optical Packet Switching Network
Continue
Transmission Network Development
Advanced Technology LaboratoriesDWDM Capacity and transmission:Technology review
Today Technology1530 - 1560 nm window (used to call C-band) 80 ~ 100 channels of 2.5 Gb/s (50 GHz spacing) 32 ~ 40 channels of 10 Gb/s (100 GHz spacing)
70 ~ 90 km span length 4 in-line optical amplifiers and 5 spans total 400 km transmission for 10 Gbit/s total 600 km transmission for 2.5 Gbit/s
Tomorrow Technology1530 - 1600 nm window (used to call L-band) 100 ~ 200 channels of 2.5 Gb/s 64 ~ 100 channels of 10 Gb/s
After…1480 - 1530 nm window by Raman amplification
Transmission Network Development
Advanced Technology Laboratories
OC-48/OC-192
OC-48/OC-192
OC-48/OC-192
OC-48/OC-192
70-90km
DWDM transmission system
70-90km
OSC 1510 nm or 1480 nm
1510 nmor 1480 nm
Tx
Uni-directional transmission
Bi-directional transmission
Transmission Network Development
Advanced Technology LaboratoriesSpan design in DWDM transmission
OC192 (10 Git/s) +6~8 dBm/ch
• 3 span: span distance 90 km, total 270 km• 4 span: span distance 80 km, total 320 km• 5 span: span distance 70 km, total 350 km
OC 48 (2.5 Gbit/s)• 3 span: span distance 120 km, total 360 km • 5 span: span distance 100 km, total 500 km • 8 span: span distance 80 km, total 640 km
Transmission Network Development
Advanced Technology LaboratoriesOptical transmitter in DWDM system: DFB laser with external modulator
DFB laser with External modulation (for backbone long distance)• Wavelength stable, narrow band DFB laser
- DFB laser spectrum width : ~ 20 mHz - wavelength stability: +/- 0.01 nm
•DFB laser integrated with EA modulator- Low chirping effect- polarization stability- low driving power required
•DFB laser with external LN modulator- polarization problem- high driving power required- chirping problem
DFB laser with Direct modulation (for local area short distance)- chirping problem- spectrum broaden- wavelength stability
Transmission Network Development
Advanced Technology LaboratoriesWavelength multiplex/demultiplex technology in DWDM: AWG, Dielectric filter, Fiber grating
WDM Mux/Demux
• AWG (array waveguide grating) - Insertion loss : 6 ~ 8 dB (insertion loss is almost- channel crosstalk ~ 25 db- application for higher channel number
• Dielectric filter WDM Mux/Demux-insertion loss: increases when channel number increases-channel crosstalk: 25 ~ 30 dB -application for lower channel number WDM Mux/Demux
• Fiber Bragg grating
- need optical circulator - cascade multipile grating to form a WDM Mux/Demux
Transmission Network Development
Advanced Technology LaboratoriesTwo-stage Optical fiber amplifier
DCF
opticalfilterOSC
980 nmpump
EDFA1
1480 nmpump
EDFA2WDM WDM
• 980 nm low noise pump laser for first stage EDFA• 1480 nm high power pump laser for second EDFA• DCF (dispersion compensation fiber) is required for 10 Gbit/s• Attenuater is needed for 2.5 Gbit/s • Optical isolator is used to reduce back ASE noise impact• Optical filter is used for gain equalization • Total gain of fiber amplifier is from 25 dB to 30 dB • N.F. (noise figure): 5 ~ 7dB• Output power : +17 ~ +23 dBm•Flatten gain : +/- 1 dB with 30 nm ~ 40 nm over Er. gain range•Dynamic input range: 15 dB
Transmission Network Development
Advanced Technology LaboratoriesOptical amplification, bandwidth , and capacity
0.25 db
0.4 db
1310 nm 1550 nm
C band: 1530 ~ 1560 nm (100 Ghz channel space for 10 Gbit/s, total 40 channels, 50 Ghz channel space for 2.5 Gbit/s, total 96 channels )
L band: 1560 ~ 1600 nm (40 channel available for 10 Gbit/s, i.e. 40 gbit/s, , and 100 channels available for 2.5 gbit/s)
S band: 1480 ~ 1520 nm (40 channel available for 10 Gbit/s, i.e. 40 gbit/s, , and 100 channels available for 2.5 gbit/s)
Fib
er
los
s
Wavelength ()
•Total 1.2 Tbit/s capacity• S Band: Raman amplification• L Band: EDFFA, Ti-EDFA• C Band: EDFA
Transmission Network Development
Advanced Technology LaboratoriesFiber nonlinearity: SPM, XPM, SBS, and FWM
SPM: Self-phase modulation - Create positive chirping, which cause pulse distortion due to fiber dispersion - Result in the optical spectrum broaden which limits the channel spaceXPM: Cross phase modulation - Phase modulation between two channels due to fiber Kerr effect - Convert phase noise (due to ASE) to intensity noise via fiber dispersion - Limit channel space (for 10 Gbit/s channel space is 100 Ghz , 0.8nm)SBS: Stimulated Brillouin Scattering - Creating a new wave in backward direction through interaction between light wave and acoustic wave - SBS threshold can be reduced by decreasing the power level and increasing optical spectrum. - For 10 Gbit/s, FM modulation (~100 Mhz) of DFB laser can reduce the SBS threshold from +5 dBm to +10 dBm.FWM: Four wave mixing - Optical parametric process through 3 or 4 light wave. - Cause nonlinear channel crosstalk when transmission near zero dispersion wavelength (a critical problem for dispersion-shift fiber) - Standard SMF-28 is good to suppress FWM, but has too much chromatic dispersion - True wave fiber has larger enough dispersion to suppress FWM, and small enough chromatic dispersion, but still has dispersion slope problem.
Transmission Network Development
Advanced Technology LaboratoriesPolarization mode dispersion limitationfor beyond 10 Gbit/s
Y
XX-polarization
Y-polarization Y-polarization
X-polarization
c, (nx-ny) and L
• PMD is caused by differential group delay (DGD) between two - polarization modes• PMD is a statistic process satisfying Maxwellian distribution• PMD becomes serious issue for 10 Gbit/s and beyond• PMD design - Instantaneous PMD should be smaller than 25% pulse width - Assuming fiber PMD is 0.3 ps/km^1/2, 400 km fiber gives mean PMD 6 ps. If we use safety number 4 for Maxwellian distribution, the instantaneous PMD is 24 ps. Which means 0.3 ps/km^1/2 PMD gives 400 km distance limitation for 10 Gbit/s.
Transmission Network Development
Advanced Technology LaboratoriesPMD compensation technology
Y
XX-polarization
Y-polarization
Transmitter Receiver
Polarizationcontroller (PC)
PM fiber
Electronicprocess
feedbackcontrol signal
Long distanceSM fiber
• PM fiber: with high PMD due to strong fiber birefringence• PMD induced by long distance single mode fiber can be canceled by using a short PM fiber with a greater PMD • Feedback control signal to adjust input polarization of PM fiber, so that the fast polarization axis of single mode fiber matches to the slow axis of PM fiber and vice versa.
Transmission Network Development
Advanced Technology LaboratoriesCapacity and transmission distance
Current Transmission Technology•1530 ~1560 nm window of EDFA - 10 Gbit/s X 16 ch transmission (channel space 0.6 nm) - 45 ~ 50 km span length - ~ 150 in-line optical amplifiers - total 7500 km transmission without electronic regenerter for 10 Gbit/s
Future Transmission Technology - 10 Gbit/s x N (N=32~50) transmission - 20 Gbit/s WDM technologies - 40 Gbit/s WDM technologies
Transmission Network Development
Advanced Technology LaboratoriesUniquely designed LCF fiber and non-zero dispersion shift fiber (NZ-DSF)
EDFA EDFALCF fiber NZ-DSF fiber
25 km 25 km
….….
• LCF (Large core fiber) - chromatic fiber dispersion -2 ps/km.nm - large effective area 75 ~ 80 um^2 - bigger dispersion slope - suppression of nonlinear effect - used in first half span distance for higher channel power • NZ-DSF fiber - chromatic fiber dispersion -2 ps/km.nm - smaller dispersion slope - used in second half span for smaller power - to reduce accumulation of chromatic dispersion
Transmission Network Development
Advanced Technology LaboratoriesChromatic dispersion compensationin Submarine transmission
EDFA EDFALCF fiber NZ-DSF fiber
25 km 25 km
..….EDFA EDFAStandard SMF fiber
50 km
….
10 span 500 km
• Standard single mode fiber (SMF) is used for chromatic dispersion compensation• Dispersion compensation is performed at every 10 span (500 km)• In order to resolve dispersion slope problem, pre-dispersion and post-dispersion compensation are needed at transmitter and receiver ends
Transmission Network Development
Advanced Technology LaboratoriesPMD concern in submarinetransmission
• how is PMD impact for ultra- long distance such as Submarine transmission (7500 km)?
- PMD is accumulated through the long distance transmission by both fiber cable and every optical component. - define a low PMD fiber (PMD as low as 0.008 ps/km^1/2). Over 7500 km, mean fiber PMD =6.9 ps . - define each optical component with a small
PMD, e.g, EDFA with 0.1 ps, WDM with 0.1ps.
Transmission Network Development
Advanced Technology LaboratoriesOne stage Er. Doped fiber amplifier
Er. fiber
980 nm pump laser module
Opt.isolator
ASEfilter
Gain equalizationfilter
• 980 nm low noise pump laser module for first stage EDFA• Optical isolator is used to reduce back ASE impact• Optical filter is used for gain equalization • ASE filter (FBG) is used to get off ASE and its accumulation• Total gain of fiber amplifier is from 10 dB to 12 dB • small N.F. (noise figure): ~4 dB• Output power : ~ +11 dBm
Transmission Network Development
Advanced Technology LaboratoriesComparison of WDM transmission between terrestrial and submarine network
• Why submarine network can transmit over 7500 km with more than 100 span and fiber amplifiers at 10 Gbit/s, but terrestrial network can only handle 5 span over 400 km? 7500 km vs/ 400 km is a big difference!
- Submarine transmission network is a pre-defined system, which is more like a well controlled experimental system in Lab.
- In terrestrial network, the characteristic of fiber in underground is unknown. The system designer should build equipment to cover a lot of statistic cases.
Transmission Network Development
Advanced Technology Laboratories
R Router
Non-IP Data Source
ATM Switch
SONET DCS or ADM
Optical XC or ADM
Optical line System
R
R
R
R
R
R
R
RR
IP/SONET
IP/WDM
Next Generation Network
IP/ATM
Transmission Network Development
Advanced Technology Laboratories
WDM Long Haul
WDM MetroBackbone ring
WDM localcollecting ring
WDM localcollecting ring
Hub
Central Node
2
3
4
5
6
Hub
1
All Optical Network: WDM Long Haul, Metro Backbone, and Local Collecting Ring
Transmission Network Development
Advanced Technology Laboratories
The ring size of metro backbone WDM network is defined to be from 100 km to 200 km, and WDM local collecting ring is defined from 20 km to 50 km.In order to have a transparent (protocol independent) transport optical network also for the low cost reason, no electronic regenerators should be allowed in Metro WDM rings.Optical amplifiers might be needed in WDM metro backbone ring network, but not in WDM local collecting ring. Metro WDM ring should be self-healing optical ring. network protection and restoration should be at photonic layer .
Description of Metro WDM Ring
Transmission Network Development
Advanced Technology Laboratories
Same interconnections between routers requires1 protection wavelength with OSPRING
Interconnections between routers requires 4protection wavelengths with path switch
Optical Protection EfficiencyOptical Protection Efficiency
1+1 OSNCP (Path Switch) vs. OSPRING (Optical Line)
5
5
5
5
OSPRING
55
55
1+1 OSNCP
Transmission Network Development
Advanced Technology Laboratories2-Fiber OMS/SPRING 2-Fiber OMS/SPRING (conventional switching)(conventional switching)
D
Ring SwitchA
B
CAC
CAACCA
fiber 1fiber 2
Working Protection
fiber 1
i - N/2 N/2 - N
(i) (k)
WorkingProtection
fiber 2
i - N/2 N/2 - N
(i) (k)
No Wavelength ConversionRequired
fiber cut
Transmission Network Development
Advanced Technology Laboratories2-Fiber OMS/SPRING 2-Fiber OMS/SPRING
(w/G.841 undersea protocol)(w/G.841 undersea protocol)
D
Ring SwitchAAC
CAACCA
fiber 1fiber 2
Working Protection
fiber 1
i - N/2 N/2 - N
(i) (k)
WorkingProtection
fiber 2
i - N/2 N/2 - N
(i) (k)
No Wavelength ConversionRequired
C
Bfiber cut
Transmission Network Development
Advanced Technology Laboratories
How to transport large pipes (OC-48c & above) reliably? Should OC-192 be deployed in an existing OC-48 based network?
Should SONET be bypassed for ATM, FR, and IP transport over wavelengths?
No standards on optical data interface, multi-vendor interoperability What survivability architecture best balances performance, cost, and
flexibility? Is synchronization required for optical network? Mechanisms for providing OCH trail trace, mechanisms to discover fiber
topology, performance monitor and management across administrative boundaries.
Meeting latency requirements in detecting, reporting, localizing, and reacting to faults (e.g. protection switching).
Optical Network Evolution IssuesOptical Network Evolution Issues
Transmission Network Development
Advanced Technology LaboratoriesSurvivability Alternative TradeoffsSurvivability Alternative Tradeoffs
DistributedMesh
Facility Cost [Restoration Overbuild]
SNCPMSP
Max
imu
m O
uta
ge
MS/SPRING
CentralizedMesh
Good Good
Goo
dG
ood
Service Layer Mesh
Physical Layer (SONET & Optical) Schemes
Every survivability mechanism makes tradeoffs:Speed vs. Facility Cost (Overbuild) is most fundamental
Every survivability mechanism makes tradeoffs:Speed vs. Facility Cost (Overbuild) is most fundamental
Transmission Network Development
Advanced Technology Laboratories
CentralNode
OADM OADMOADM
OADM OADMOADM
Metro WDM Network’s Key Issue: Limited Number of OADM Nodes and Small Ring Size
Transmission Network Development
Advanced Technology Laboratories
CentralNode
OADM OADMOADM
OADM OADMOADM
OADM
OADM
1
8
1 2 3 4
5678
Boost-Amp
Pre-Amp
Metro WDM Network’s solution: Boost and Pre-Amplifiers
Att.
Transmission Network Development
Advanced Technology Laboratories
CentralOffice
OADM OADM OADMOADM
OADM OADM OADM OADM
1 2 43
1234
8
..
8 7 6 5
...
12 8
32815 7
4
3 815 7
ATT.ATT
4
EDFA Input (beforeTx ATT)
EDFA Input (after ATT control)
EDFA
EDFA Output
Metro WDM Network’s solution: One Line-amplifier
Transmission Network Development
Advanced Technology LaboratoriesMetro WDM Network’s solution: Line-Amplifier with Gain Slope
CentralOffice
OADM OADM OADMOADM
OADM OADM OADM OADM
1 2 43
4328
1234
8
..
EDFA Input
8 7 6 5
...
4 3 8
Gain curve
15 7
EDFA
EDFA Output
Transmission Network Development
Advanced Technology LaboratoriesMetro WDM Network: Experimental Set-up
A
B
C
DTX
RX
LR
Splitter
A
B
B
A
A
D
C
B
7dB7dB
7dB
TXTX
RX
SR
Client
Combiner
7dBRX
Switch
OADMfilter
Transmission Network Development
Advanced Technology LaboratoriesTransparent WDM Network: SONET-Less , Photonic Layer Restoration By Metro WDM Equipment
Metro WDMNetwork 1
A D
Hub Hub
OADM
WDM Long Haul Network
OADM
OADMOADM
Metro WDM
Network 2
Hub
Metro WDM
Network 3
c
B
Transmission Network Development
Advanced Technology Laboratories Hybrid WDM Metro and Long Haul: Experimental Set Up
LA2Erroroutput
Fiber cut
16 ch. Long Haul WDM Transmission 500 km
Tektronix ST2400 SONET testset
Transponder
Metro WDM Network 1
DA
C
B
:
’
..
.
E
F
G
:
’
:
’
A E
Fiber
40 ch. Long Haul WDM Transmission 500km
EA
C
C
F
FH
HP DigitalScope
:
’
LA1
LA3
LA4
TA RA
Transmission Network Development
Advanced Technology Laboratories
Error freeError free
Error period
Protection time when 16 channel long haul
WDM fails
Transmission Network Development
Advanced Technology Laboratories
Error freeError free
Error period
Protection time when 40 channel long haul
WDM fails
Transmission Network Development
Advanced Technology LaboratoriesBER results for working and protection path
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
-34 -33.5 -33 -32.5 -32 -31.5 -31 -30.5
Receiving power (dBm)
BE
R
working pathprotection path with other Metrio traffics (working path)
Transmission Network Development
Advanced Technology LaboratoriesEmerging Technology: Optical CDM (CDMA) using Fiber Brag Gratings
FBG n...
Optical circuit
“1”
1 2 n
d
t
“1 0 1 0 0 1 ”
FBG n...
1 2 n
d
t
“1 0 1 0 0 1 ”
“1”
Output
Input
Dispersion Compensation
Fiber
EDFA
Transmission Network Development
Advanced Technology LaboratoriesOptical Packet Switching NetworkOptical Packet Switching Network
Node
2
Node
1
Node
100
Node
4
Node
5
Node
3
IP/ATM
Network
IP/ATM
Network
IP/ATM
Network
IP/ATM
Network
IP/ATM
Network
IP/ATM
Network
Optical packet switching ring network
….
100
1
2
5
4