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Optische netwerkenSNE opleiding - 19 maart 2009
Roeland Nuijts, SURFnet, The Netherlands
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
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)