T r ansmission Network Development Advanced Technology Laboratories DWDM Transmission Technology and...

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



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



- 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



- 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


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



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


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


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


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


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


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


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.


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.


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.


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


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


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


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.


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


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.



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



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



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



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


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


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



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


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



CentralNode

OADM OADMOADM

OADM OADMOADM

Metro WDM Network’s Key Issue: Limited Number of OADM Nodes and Small Ring Size



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.



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


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


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


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


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



Error freeError free

Error period

Protection time when 16 channel long haul

WDM fails



Error freeError free

Error period

Protection time when 40 channel long haul

WDM fails


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)


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


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

T r ansmission Network Development Advanced Technology Laboratories DWDM Transmission Technology and...

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