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Optische netwerkenSNE opleiding - 19 maart 2009

Roeland Nuijts, SURFnet, The Netherlands

roeland.nuijts@surfnet.nl

Outline

- Introduction

- Optical transmission fiber

- Optical transmitters and receivers

- DWDM enabling technologies

EDFA (E bi D d Fib A lifi )- EDFAs (Erbium Doped Fiber Amplifiers)

- Optical multiplex and demultiplex filters

- 10Gb/s transmission and Dispersion compensationp p

- High-speed transmission (40Gb/s and 100Gb/s)

- All optical switching – WSS (Wavelength Selective Switches)

2

Optical fiber - Historical perspective

- Basic principle of internal reflection

known from 19th century (John

Tyndall, 1870)

E l fib ith l ddi t l - Early fibers with cladding extremely

lossy ~1000dB/km (1960)

- Progress in fabrication (MCVD)

leads to low loss fibers (0.2dB/km

at 1550nm wavelength, limited by

fundamental limit of Rayleigh

scattering) around 1979

3

Fiber absorption

- Fiber loss is wavelength dependent, minimum is around 1550nm- Current fiber loss is close to fundamental limit determined by Rayleigh

scattering, proportional to l-4 therefore dominant at short wavelengths- Loss at long wavelengths (l > 1625nm) dominated by infra-red absorption

4

- Peak at 1400nm arises from OH impurities, can be removed (AllWave fiber)

Fiber dispersion - Refractive index varies with wavelength which leads to a wavelength dependence of the group delay, tg, (delay for different gwavelengths) in ps/km

- Dispersion coefficient, D, is the derivative of the group delay, tg , with respect to wavelength per unit length (ps/nm km)tg

(ps)

1 2

1,4 Optical pulse shape at Tx output

λ (nm)0,0

0,2

0,4

0,6

0,8

1,0

1,2

4100 4300 4500 4700 4900 5100 5300 5500

Opt

ical

Pow

er (A

.U.)

D(ps/nm km)

0-30 -20 -10 0 10 20 30

Frequency (G Hz)

4100 4300 4500 4700 4900 5100 5300 5500

Time (ps)

0λ (nm) -5

-10

-15Pow

er(d

B)

Optical spectrumat Tx output

l0

5

-30

-25

-20

15

Optic

alP

• No distortion at zero-dispersion wavelength, l0• Distortion at other wavelengths

Optical fiber Historical perspective “Standard SMF Optical fiber – Historical perspective “Standard SMF (G.652)”

- Initial (80’s) optical components for transmission through single mode fiber operated at the 1.3 mmwavelength, therefore fiber was developed which had zero-dispersion at this wavelength. For this wavelength, therefore fiber was developed which had zero dispersion at this wavelength. For this reason, this type of fiber is often referred to as “standard fiber”, “conventional fiber” or “ITU G.652 fiber”.

- Installed fiber base in the world is mainly comprised of this standard (1.3µm zero-dispersion wavelength) SMF (Single Mode Fiber)

- This embedded base represents an enormous investment, strong incentive to use it

- Development and commercialization of sources and detectors operating in the 1550nm wavelength region, where the minimum fiber loss is achieved, were developed later, more specifically in the 80’s

- Dispersion-Shifted Fiber (zero-dispersion at 1550nm) later developed and deployed, predominantly in Japan

17

6

NZDSF (Non-Zero Dispersion Shifted Fiber) optimizes dispersion in the EDFA region

7

Introduction – Traditional digital point-to-point Introduction Traditional digital point to point optical fiber transmission systems

Transmission fiber

Tx Rx

a (dB/km)

Tx Rx

PT (dBm) PR (dBm)

T itt d l i l “ ” d “ ” b t i li ht “ ” d “ ff” i

Transmission distance = (PT-PR) / a (km)

- Transmitter sends logical “ones” and “zeros” by turning light “on” and “off”, receiver converts received optical power to electrical signal, retrieves clock signal and determines on decision moment whether “one” or “zero” was sent

- Initial, low-speed, optical fiber transmission systems were “loss-limited”, transmission distance was limited by the thermal noise in the optical receiverdistance was limited by the thermal noise in the optical receiver

- Increase in transmission bit rate to high speeds (bit rate ≥ 2.5Gb/s) has made fiber dispersion, D, an important system parameter which limits the achievable transmission distance

8

Decibel scale versus li llinear scale

• Power levels and loss scales in optical systems cover a hugh dynamic range• Power levels and loss scales in optical systems cover a hugh dynamic range

• Losses in fibers and filters are multiplication factors in linear domain, additions and subtractions in dB

• Typically power levels and losses on logarithmic scale in decibels, more practical

• Power is mW in linear domain -> dBm in logarithmic domain

• Loss dimensionless in linear domain -> dB in logarithmic domain

P (mw) P (dBm) P (mw) P (dBm)

(mW)] [P Log 10=(dBm) P 10

[L]Log10=(dB)L 10

1000 30 1 0800 29 0.8 -1500 27 0.5 -3400 26 0.4 -4250 24 0.25 -6200 23 0 2 7[L]Log 10(dB)L 10 200 23 0.2 -7100 20 0.1 -1080 19 0.08 -1150 17 0.05 -1340 16 0.04 -1425 14 0 025 -1625 14 0.025 1620 13 0.02 -1710 10 0.01 -208 9 0.008 -215 7 0.005 -234 6 0.004 -24

x 2 ª 3dBx 5 ª 7dBx10 ª 10dB

9

2 3 0.002 -271 0 0.001 -30

0 0d

10Gb/s optical transmitter technologies

{0,1,1,0,1,1,…,0,1,0}

DFB

DM-DFB (Directly Modulated Distributed Feed Back laser)• Cheap, small, low power consumption• Chirped, i.e. different wavelength during “ones” and “zeros” which leads to a wide optical spectrum and associated transmission impairments• Used for short reach transmission

EML (El t Ab ti M d l t L )

{0,1,1,0,1,1,…,0,1,0}

DFB EA

EML (Electro-Absorption Modulator Laser)• Monolithically integrated laser and modulator combination• Potentially cheap, small, medium power consumption• Chirped, i.e. different wavelength during “ones” and “zeros”• Used for intermediate and long reach transmissiong

{0,1,1,0,1,1,…,0,1,0}CW-DFB (Continuous Wave DFB laser) and MZ (Mach-Zehnder) combination

DFB

(Mach Zehnder) combination• External modulator• Expensive, relatively large, high-power drivers (high power consumption)• Low (or deterministic) chirp, excellent

f

10

Mach-ZehnderLiNbO3 modulator

performance• Used for long reach and DWDM (Dense Wavelength Division Multiplexing) transmission

Typical 10Gb/s optical receiver setup

preamp AGCdecisioncircuit

data

CLK

(A)PD

• Photodetector converts optical signal to electrical signal. PIN or APD (Avalanche Photo Detector) for improved receiver sensitivity

P id hi h i l i

BER

• Preamp provides high gain, low noise

• AGC (Automatic Gain Control) amplifies signal at output of preamp to rail-to-rail voltage of decision circuit

• Decision circuit, usually D-flip-flop, signal at input is clocked to the output on rising edge of clocksignal distortion is removed

10-9

10-6

rising edge of clocksignal, distortion is removed

• BER (Bit-Error Rate) performance limited by thermal noise in receiver, receiver performance is usually specified in terms of receiver sensitivity, i.e. the amount of optical power needed to achieve a BER of 10-12

10-12

Psens

11

Prec (dBm)

WDM enabling technologies I: WDM enabling technologies I: EDFAs (Erbium Doped Fiber Amplifiers)

• Fiber doped with Er3+ ions be excited by 980nm or 1480nm photonsp y p• spontaneous emission generates noise• Excited state Erbium ions can be stimulated to decay to ground state via stimulated emission by a 1550nm signal

12

Erbium Doped Fiber Amplifier

Erbium DopedFiber

isolator isolator

1480nmoror

980nm

13

ASE (Amplified Spontaneous Emission)

() = 2 h n sp (G() – 1)

- Amplifiers are used to overcome fiber losses.- Optical Noise is added by each amplifier.

14

- Engineering rules usually defined for equal spans (e.g. 20 x 20dB) which is not the case in the real fiber networks

Slide courtesy of Kim Roberts, Nortel

Initial two-stage EDFA configuration, Initial two stage EDFA configuration, example

• High-gain, low-noise first stage followed by high-power second stage

• Current designs state of the art designs are wideband, 1520nm-1560nm (C-band) or 1565nm-1605nm (L-band), can be used for simultaneous amplification of multiple channels at different wavelengths

• Bitrate transparent

15

• Fiber loss no longer limiting factor

WDM enabling technologies II: WDM enabling technologies II: Multiplex/Demultiplex filters

• somewhat analogous to prism• input white beam, seperates it spatially onto output fibers• works both ways, demux and mux• other technologies possible (e.g. thin film filter)

16

g p ( g )

WDM system configuration (one-way)C

MD 1

CM

D

1TxTxTxTx

λ1

RxRxRxRx

Add/drop siteG

MD

CM

D 2

OA OA OA OA

GM

D

CM

D2

Tx Rx

OA

GM

DG

MD

OA

G

CM

D 9

D

CM

D

9TxTxTx

RxRxRx

DG

CMD CMD

Tx = 10Gb/s Optical transmitter(OM5200/OME6500)

Rx = 10Gb/s Optical Receiver (OM5200/OME6500)

λ36

C

DTxTx

RxRxT

xTx

Tx

Tx

Rx

Rx

Rx

Rx

GMD = Group Multiplexer/Demultiplexer

CMD = Channel Multiplexer/Demultiplexer

OA = Optical amplifier

S l bl d fl ibl d i t dd l th • Scalable and flexible design, easy to add wavelengths • Initial release uses 36 channels spaced at 100GHz• Can be upgraded to 72 channels, each operating at 10Gb/s• Optical add and drop for point-to-point optical lightpaths

17

Optical add and drop for point to point optical lightpaths

SURFnet6 Subnetwork 3SURFnet6 – Subnetwork 3Optical spectrum at output of transmit OA in Amsterdam1

(RB=0.5nm)

-20

-15

-10

λ1

-55

-50

-45

-40

-35

-30

-25

Pow

er (d

Bm

)

GM

D

CM

DC

MD

1

2OA OA OA OA

GM

D

CM

DC

MD

1

2

TxTxTxTx

λ1RxRxRxRx

OA

GM

D

GM

D

OA

Add/drop site

-601526 1530 1534 1538 1542 1546 1550 1554 1558 1562 1566

Wavelength (nm)

OSNR (0.1nm) > 40dB

λ36

G

CM

D 9

CM

D9

TxTxTxTx

RxRxRxRx

G

CMD CMD

Tx

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Optical spectrum at output of receive OA in Amsterdam1(RB=0.5nm)

-35

-30

-25

-20

-70

-65

-60

-55

-50

-45

-40

Pow

er (d

Bm

)

• Subnetwork 3 specific• eight spans• total distance 528km• dispersion optimized to allow traffic between any pair of sites

1526 1530 1534 1538 1542 1546 1550 1554 1558 1562 1566

Wavelength (nm)

OSNR (0.1nm) > 28dB

18

Dispersion limited di t Ldistance, LD

1

F r eq u e n c y ( G H z )

DBLD

1 B = 10 Gb/sD = 17 ps/nm km LD = ~50kmΔλ = 0.112 nm*

- 30 - 2 0 -1 0 0 1 0 2 0 3 0

-5

1 0

(dB

)

q y ( )

0 8

1,0

1,2

1,4

er (A

.U.)

- 20

-1 0

- 15

ptic

a lP

ow

er

0,0

0,2

0,4

0,6

0,8

4100 4300 4500 4700 4900 5100 5300 5500

Opt

ical

Pow

e

• Chromatic dispersion places a limit on the maximum transmission distance• L scales with square of the bitrate

- 30

- 25OTime (ps)

• LD scales with square of the bitrate• 50km at 10Gb/s, hence dispersion compensation is needed in case of

transmission beyond 50km• 3km at 40Gb/s, if you would use NRZ

19

• Linear effect, can be compensated by fiber with negative dispersion

* 3dB bandwidth of 7GHz assumed, doublesided spectrum 14GHz ≡ 0.112nm

Example of impact of dispersion on transmission systemExample of impact of dispersion on transmission systemperformance - optical pulse shape of 10Gb/s signal after 120km

120km standard SMF

Tx

D=17.8 ps/nm km

RxOA ƒ

r 10Gb/s

OA

12

1,4

120km-10Gb/s system configuration

rb = 10Gb/slc = 1557nm

0,0

0,2

0,4

0,6

0,8

1,0

1,2

4100 4300 4500 4700 4900 5100 5300 5500

Ti ( )

Opt

ical

Pow

er (A

.U.)

1

Time (ps)

Optical pulse shape at transmitter output

• Pulse shape after 120km transmission completely distorted due to pulse broadening, error-free transmission not possible

20After 120km transmission2

Dispersion Compensating FiberDispersion Compensating Fiber

Standard fiberDispersion compensating fiber

D(ps/nm km)(ps/nm km)

0λ (nm)

l0, SMF

1310nm

lT

1550nm

l0, DCF

• Advantages• Wide band compensation (one DCF compensates for all channels in C-band)

• Feasible for DWDM systems• Easy to use reliable• Easy to use, reliable

• Disadvantages• bulky• DCF loss, requires additional optical amplifier• smaller core area, hence nonlinear effects

21

Measured and calculated optical pulse shape after 120km and after DCF

fTx RxA1 A2 A3

ATT1 ATT2 ATT3120kmSMF DCF

After 120km transmission

1 2 3, 1

• Pulse shape after 120km transmission completely distorted due 2

After compensation, PDCF =+5dBm

to pulse broadening, error-free transmission not possible • Optical pulse shape recovered after passing through DCF with negative dispersion• More residual dispersion if optical power level at the input of the DCF is high due to the (undesirable) 3

After compensation, PDCF = 0dBm

nonlinear effect in the DCF

Linear Dispersion Pre-compensatorcompensator

hr(t) DAC LPF

M-Z

CW sourceData

I

hi(t) DAC

M-Z 90o

QLPF

Filter complexity scales linearly with Dispersion

Slide courtesy of Kim Roberts, Nortel23

EDC (Electrical Dispersion Compensation)

{0 0 0 0}

Total 5000km standard transmission fiberH(f)

DFB+MZ Rx

{0,1,1,0,1,1,…,0,1,0}H(f)

≈h-1 (t) OA OA OA

Optical Power Arb . Units Optical Power Arb Units

DFB+MZ≈h 1 (t) OA OA OA

1 2

1

1.5

2

2.5

1

1.5

2

2.5Optical Power Arb . Units

D=+87500ps/nmEDCoff

2

2.5Optical Power Arb . Units

2.5Optical Power Arb . Units

4400 4600 4800 5000 5200 5400time ps

0.5

4400 4600 4800 5000 5200 5400time ps

0.5

z=0km z=5000km

0.5

1

1.5

2

0.5

1

1.5

2D=-87500ps/nmEDCon

24

4400 4600 4800 5000 5200 5400time ps

4400 4600 4800 5000 5200 5400time ps

z=0km z=5000km

No more need for dispersion compensation via DCFs (Dispersion Compensating Fibers)!!

How to do 40Gb/s on current infra?How to do 40Gb/s on current infra?QPSK (Quadrature Phase Shift Keying) 2 Bits per Symbol

OOK QPSK

Q

OOK(On-Off Keying)

QPSK

I(0) (1)

40Gb/ D l l i ti40Gb/s - Dual-polarization

Vertical Polarization

Horizontal PolarizationPolarization

Dual Polarization

40G Dual Polarization QPSK has the same 40G Dual Polarization QPSK has the same symbol duration as 10G

40G Dual Polarization QPSK40G Dual Polarization QPSK

100 ps

10G Conventional TDM

100 ps

40G Conventional TDM

100 ps

40G Conventional TDM

Time25 ps

Time

40G Dual Polarization QPSK has the same 40G Dual Polarization QPSK has the same bandwidth as 10G

40G Dual Polarization QPSK40G Dual Polarization QPSK50 GHz

10G Conventional TDM

40G Conventional TDM40G Conventional TDM

Frequency

T l Cit 2 A t dTeleCity2, Amsterdam

SURFnet, grensverleggend verbinden30

N t l OME6500 d CPLNortel OME6500 and CPL

DSCM (dispersionCompensation)

10Gb/s WDM transmitter andreceiverOME6500 CPL

GMD

CMDCompensation)receiver

SURFnet, grensverleggend verbinden31

Characteristics of dark fiber for DWDM transmission systemsDWDM transmission systems

Fiber type Average measured Total length (km)yp gtotal loss (dB/km)

g ( )

G.652 0.26 1528 (52%)

TWRS 0 23 1271 (43%)TWRS 0.23 1271 (43%)

LEAF 0.25 156 (5%)

Total 0.25 2955(100%)

12

14

Fiber span length distribution

( )

hi h t b f (12 t f 51) i

4

6

8

10

12 • highest number of spans (12 out of 51) in 80km range, which was the maximum length in the CFP (Call for Proposals) for the dark fiber bidding process. 96% of span lengths a e belo 90km

0

2

4 • 96% of span lengths are below 90km, system engineering rules allow multiple span losses of at about 23dB

32

Fiberdatabase with SRLG (Shared Risk Link Groups)

34

SURFnet6 DWDM on d k fibdark fiber

Hamburg

Münster

35

Aachen

>8800km dark fiber pairs (2955km for DWDM)

WSS Principle of operation

i t

collimatinglenses

F

inputinputoutputinputinput

common

F

36

MEMS mirror array(1 pixel per channel)

DAS-3 (Distributed ASCI S t 3)Supercomputer-3)

DRAC

HilversumDAS-3 Switch

DAS-3 Switch

- Full wavelengths in the network

HilversumDAS-3 Switch

DAS-3 Switch

DRAC

Amsterdam 1

6

346 5 3 12

controlled by users / applications Amsterdam 1

6

346 5 3 12

Leiden Delft6

4

3

1

2

6

4

2

1

1

3

2

7

DAS-3 Switch

DAS-3 Switch

3 55 5

- Allow massive bandwidth changes

Leiden Delft6

4

3

1

2

6

4

2

1

1

3

2

7

DAS-3 Switch

DAS-3 Switch

3 55 5

1

7 between two sites

Network service:

1

7

Amsterdam VU7531

DAS-3 Switch

2- Network service:

similar control as ‘standard’ dynamic

Amsterdam VU7531

DAS-3 Switch

2

37

Switch ylightpaths

Switch

ASCI = Advance School for Computing and Imaging

DAS-3 – system configurationconfiguration

WSS WSS

DelftLeiden

WSS Branching

Node

WSS Branching

NodeCluster

OM

ECM

D

Cluster

OM

ECM

D

OMECMD

OMECMDCMD

Cluster

CMD

Cluster University ofAmsterdam

AMS-VU DAS-3 Equipment

38

Nortel/SURFnet Equipment

Network topologies

Star network Ring networkMesh networkTUD

1,7

85

TUD VU

35

7TUD VU

3

5

7

UvA

2, 34,61 1

3

4

8 2

U A LU

1 1

4

8 2

VULU 1 UvA LU4 UvA LU4

6

TUD

DAS-3 optical channel1 2 3 4 5 6 7 8

UvA

Leiden

VU

39

DRAC (Dynamic ResourceAllocation Controller)Allocation Controller)

Web GUI Web GUI screenshot

40

F t lFuture plans

- Further introduce eDCO and eROADM- Further introduce eDCO and eROADM- Introduce 40Gb/s transmission on existing

infrastructure- Multi-domain control plane interworking (DRAC)- Test new technology, e.g. PBT (Provider Backbone

T anspo t) Transport) - Further enhance monitoring and reporting

41

Thanks for your attention!Thanks for your attention!

Questions?Questions?

roeland.nuijts@surfnet.nl

42

SURFnet6O ti l M d lOptical Modeler

43

FOM (Figure of Merit) f fib for fiber spans

L

N

j

L j

FOM1

1010Lj, span losses in dBN, number of spans

120km 120km 120km 80km 80km 80km

Total 600km

A

B80km 80km 80km 120km 120km 120km

100km 100km 100km100km100km 100kmC

FOMA 5504B 5504

flEasy-to-use formula that accurately quantifies transmission system performance

4444

B 5504C 1897

quantifies transmission system performancefl FOM requirement used in Call for Proposals for 1600km Amsterdam – Geneva fiber link

For more information contact Roeland Nuijts, SURFnet

OSNR (Optical Signal-to-Noise Ratio) - Simple formula( p g ) p

SMFDCF

repeater

DCFSMFSMF

Tx RxOA OA OA OA OA

P P P P P

NF1

NF2 NF3 NFN-1 NFN

ƒ

OSNR

N

jspNRh ,21

Pin,1 Pin,2 Pin,3 Pin,N-1 Pin,N OSNR

R l ti b d idth 0 149

j jinPOSNR 1 ,

Resolution bandwidth = 0.1nm

35373941434547

ated

OS

NR (d

B)Parameter Description

h Planck's constant (J•s)

c speed of light (m/s)

2527293133

0 40 80 120 160 200 240 280 320 360 400

Distance (km)

Calc

ul

c speed of light (m/s)

R OSA resolution BW (Hz)

Pin Input power (W)

Distance (km)

Simple formula, accurate to within a few tenths of a dB

45

Nsp Noise Figure (linear)