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Basic principlesof fibre optic systems
RIGA 29 sept
Lars RisbyADVA Optical Networking [email protected]
+46702596606
© 2006 ADVA Optical Networking. All rights reserved.2
WDM Services, Bit Rates
iEthernet (10 Mb/s)iIBM Token Ring (16 Mb/s)
iPDH E3 (34 Mb/s)
iDS3 / T-3, Frame Relay (45 Mb/s)iSONET OC-1 (52 Mb/s)
iFDDI, Fast Ethernet (100 Mb/s)
iT-3D, DS3D (135 Mb/s)
iPDH E4 (140 Mb/s)iATM 155, STM-1, OC-3 (155 Mb/s)
iESCON (200 Mb/s)
iDigital Video (266 Mb/s)iPDH E5 (565 Mb/s)
iATM 622, STM-4, OC-12 (622 Mb/s)iFibre Channel, FICON, Coupling Link (1.062 Gb/s), iGigabit Ethernet, OC-24 (1.25 Gb/s)
iSCSI (max. 1.28 Gb/s)
iHDTV (1.485 Gb/s)
i2Gb Fibre Channel (2.124 Gb/s)iATM 2.5G, STM-16, OC-48 (2.5 Gb/s)
i4Gb Fibre Channel (4.248 Gb/s)
iSTM-64, OC-192, 10GbE (10 Gb/s)iSTM-256, OC-768 (40 Gb/s)
© 2006 ADVA Optical Networking. All rights reserved.3
FibersFibers
© 2006 ADVA Optical Networking. All rights reserved.4
Bit-Rate × Length Product
� The Bit-Rate × Length Product (RB × L) is a convenient measure for the maximum capacity of either fibers or transmission techniques
� RB × L can be used for a ranking of fiber types, or transmission techniques – different fiber types and all transmission constraints can be considered
� RB × L is the maximum product of bit-rate RB and regenerator-less link length L
� L depends on RB !!! (or vice versa)
© 2006 ADVA Optical Networking. All rights reserved.5
� Bandwidth vs. Transmission distance
� VDSL may provide up to ~50 Mb/s at 1 km
� Fiber’s theoretical limit is in the 25 Tb/s range,the max. regenerator-less link length is several 1000 km
� Environmental stability
� Copper affected by environment from the moment of installation
� Optical signals not affected by ambient electrical noise (EMI)
� Glass is a dielectric
� Virtually eliminates shorting and lightning hazards
� Security
� Optical signals difficult to “tap” without detection
Fiber vs. Copper
© 2006 ADVA Optical Networking. All rights reserved.6
Fiber Types I
Graded-Index Multi-Mode Fiber� ITU-T G.651
� Improved Multi-Mode fiber
� Reduces Mode Dispersion through graded refractive index
� Still in use for some LAN applications, e.g. GbE
RB × L Indicator
G.651
© 2006 ADVA Optical Networking. All rights reserved.7
Standard Single-Mode Fiber (SMF)� ITU-T G.652
� Optimized for (single-channel transmission at) 1310 nm by eliminating dispersion at 1310 nm
� Dispersion at 1550 nm is much greater than at 1310 nm
� Suitable for DWDM transmission at 1550 nm
� Most common fiber deployed today
Fiber Types II
RB × L Indicator
G.651
G.652
© 2006 ADVA Optical Networking. All rights reserved.8
Dispersion Shifted SM Fiber (DSF, DSSM Fiber)� ITU-T G.653
� Zero dispersion shifted from 1310 nm to 1550 nm
� Great for single channel 1550 transmission at high data rates
� Breeding ground for Four-Wave Mixing –Not suitable for high data rate DWDM over long distances
Fiber Types III
RB × L Indicator
G.651
G.652
G.653
© 2006 ADVA Optical Networking. All rights reserved.9
Non-Zero Dispersion Shifted SM Fiber (NZ-DSF)� ITU-T G.655
� Examples: Corning E-LEAF®, Lucent TrueWave-RS®
� Developed specifically for DWDM
� Compromise between no dispersion for high data rates and enough dispersion to combat FWM
� New fiber or choice for new installations
Fiber Types IV
RB × L Indicator
G.651
G.652
G.653
G.655
© 2006 ADVA Optical Networking. All rights reserved.10
Refractive Index Profile
50 µm
r
n
r
125 µm
9 µm
125 µm
r
5 µm
125 µm
G.651 GI-MM G.652 SMFG.653 looks similar
G.655 NZ-DSF
Core
Cladding
nCO
nCL
Weakly guiding single-mode fibers: nCO ≈ nCL ≈ 1.45
© 2006 ADVA Optical Networking. All rights reserved.11
Transmission Transmission
ConstraintsConstraints
© 2006 ADVA Optical Networking. All rights reserved.12
Linear and non-linear Effects:
� Linear
� Attenuation
� Mode Dispersion, if applicable
� Chromatic Dispersion
� Polarization-Mode Dispersion, PMD
� Non-linear
� Self-Phase Modulation, SPM
� Cross-Phase Modulation, XPM
� Four-Wave Mixing, FWM
� Stimulated Raman-Scattering, SRS
� Stimulated Brillouin-Scattering, SBS
Transmission Constraints
© 2006 ADVA Optical Networking. All rights reserved.13
1300 1400 150012001100 1600900 1000800
0
0.5
1.0
1.5
2.5
2.0 OH absorption
Wavelength (nm)
Attenuation (dB/km)
1st Window
2nd Window 3rd Window
1 nm
DWDM Region
Attenuation
© 2006 ADVA Optical Networking. All rights reserved.14
Attenuation
� Signals are attenuated by
� Rayleigh Scattering (towards shorter wavelengths)
� Infra-Red Absorption (towards longer wavelengths)
� Fiber bends for bend radii < 10 mm
� Micro-Bending, induced by cabling
� (Connectors)
� (Splices)
� Attenuation can be compensated by (optical) amplifiers
� Attenuation leads to bit errors through decreased Signal/Noise Ratio (SNR), where noise sources are either receiver electronics, or optical amplifiers
© 2006 ADVA Optical Networking. All rights reserved.15
Attenuation
• Attenuation of SMF
– a = 0,35...0,50dB/km @ 1300nm
– a = 0,18...0,25dB/km @ 1550nm, industry typical 0.21 dB/km
© 2006 ADVA Optical Networking. All rights reserved.16
Mode Dispersion
Graded-Index Multi-Mode G.651
Light transmission through refraction
Mode Dispersion ~1 ns/km
B × L = 1 GHz ⋅ km
SMF G.652, G.653, G.655
Transmission through wave guidance
No Mode Dispersion
B × L > 100 THz ⋅ km
Cladding Core
Cladding Core
Mode trajectories
© 2006 ADVA Optical Networking. All rights reserved.17
Effect of Dispersion
� All dispersion effects cause pulse spreading
� This leads to pulse overlap and consequently bit errors
� Dispersion (chromatic, PMD) can partly be compensated
Direction of propagation
Env
elop
e
Pulse Center
Bit Duration T Bit Duration T Bit Duration T
© 2006 ADVA Optical Networking. All rights reserved.18
Effect of Dispersion
Time
Rec
eive
Sig
nal
Tra
nsm
it S
igna
l
Decision window:Will this be detected as „0“???
0 01
Pulse Overlap(Inter-Symbol Interference)
11
© 2006 ADVA Optical Networking. All rights reserved.19
Chromatic Dispersion
Dispersion Compensation
Time Time
Dispersion:SMF @1310 nmDSF @ 1550 nm
Dispersion:SMF @ 1550 nmDSF @ 1310 nm
Pow
er le
vel
© 2006 ADVA Optical Networking. All rights reserved.20
D states pulse spreading per link length and per bandwidth
Chromatic Dispersion is described by the Dispersion Parameter D
Chromatic Dispersion
1310 nm 1550 nm
D[p
s/(n
m k
m)]
Standard SMFG.652
DSF G.653
λ [nm]
NZ-DSF G.655
20
10
0
-10
-20
© 2006 ADVA Optical Networking. All rights reserved.21
Polarization-Mode Dispersion
� Two orthogonal Polarization Modes in SMFs, these propagate with different velocities due to non-perfect fiber symmetry
� Causes time spreading of pulses
� Strong increase with bit rate,systems with >2.5 Gb/sper channel affected
Direction of propagation
V H-Polarization
V V-Polarization
PMD Coefficient DPSMF: DP = 0.1-0.5 ps/√km
© 2006 ADVA Optical Networking. All rights reserved.22
Dispersion Compensation
� Dispersion Compensation is necessary for channel bit-rates of >2.5 Gb/s and regenerator-less link lengths of >50 km(e.g. >800 km @ 2.5 Gb/s or >50 km @ 10 Gb/s)
� Chromatic dispersion can easily be compensated by means of compensation fibers (change sign of D parameter or other dispersive components like Bragg grating fibers
� PMD must be considered for systems carrying 10 Gb/s per wavelength or more. Due to its statistical nature it is more difficult to compensate, however compensators based on turnable fiber curls exist…in practise more or less in labs
© 2006 ADVA Optical Networking. All rights reserved.23
Fiber Non-linearity
Non-linearity means that new spectral components– noise signals! – can potentially be generated
Non-linear System
Input:A1 · gI(f) + A2 · gI (f )
Output:B1 · gO(f ) + B2 · gO(f ) + Noise(f)
© 2006 ADVA Optical Networking. All rights reserved.24
Various effects caused by-
-Too high powers
-Not enough dispersion!
Important to realize you cannot do everything in WDM system-and that it is an analogue system!
Non linear effects
© 2006 ADVA Optical Networking. All rights reserved.25
EDFAsEDFAs
© 2006 ADVA Optical Networking. All rights reserved.26
EDFA Principle
� Based on Er+-doped fibers
� Erbium well-suited for 3rd optical window around 1550 nm
� Erbium leads to very efficient amplifier design
� Traveling-Wave Laser amplifier
� Pump Laser needed for energy supply (980 nm, 1480 nm)
Pump Laser Diode
Er+-Fibre
Frequency
Power
Frequency
Power
Input Spectrum Output Spectrum
© 2006 ADVA Optical Networking. All rights reserved.27
EDFA Characteristics
� Ultra-broadband amplification:
� ~1530 – 1570 nm (C-Band, ~5 THz)
� ~1570 – 1610 nm (L-Band, ~5 THz)
� High (small) signal gain, up to 35 dB
� High output power, up to +20 dBm
� Transparent for bit-rate, protocol
� EDFA tilt-important to control ( Different amplification at different wavelengths)
� Can lead to crosstalk between WDM channels
� Power control necessary
� Cost driver
© 2006 ADVA Optical Networking. All rights reserved.28
EDFA Management
� Multi-channel EDFAs need power control
� In-Line EDFAs need supervisory channel
PDPLD
Demux
OSC
Control
Management FunctionsOSC
Er+-Fiber
Frequency
Power
Frequency
Power
OSC: Optical Supervisory Channel PD: Photo Diode PLD: Pump Laser Diode
© 2006 ADVA Optical Networking. All rights reserved.29
Sub-Band EDFAs
� One EDFA per Sub-Band
� In-Line amplifier needs band splitter
� No power level control necessary
� More robust against channel failures
� Flexible link design possible
PL
PL
PL
PL
BandSplitterModule
BandSplitterModule
Band 1
Band 2
Band 3
Band n
© 2006 ADVA Optical Networking. All rights reserved.30
WDMWDM
© 2006 ADVA Optical Networking. All rights reserved.31
What is WDM?
� WDM means Wavelength Domain Multiplexing
� It is Frequency Domain Multiplexing at optical frequencies (~200THz)
� It can be divided into
� Dense WDM (DWDM), 200, 100, 50 GHz grid)
� Coarse WDM (CWDM), channel spacing >> channel bandwidth (e.g. channels at 1470 nm, 14900 nm, …1550 nm,… 1610nm)
� 8 channels with G652 waterpeak fibre-16 ch with lo/no water peak
� Funny tricks-you can do 1310 at same time as you do 1550 CWDM..
© 2006 ADVA Optical Networking. All rights reserved.32
� Early 80’s� AT&T used dual wavelength CWDM in experiments on Trans-Atlantic cable
� Mid 80’s� Dual wavelength CWDM in commercial use
� Field trials Sweden 1987
� 1986� EDFA invented
� Early 90’s� First commercial deployment of DWDM systems-CIENA
� Mid 90’s� Non-Zero Dispersion Shifted Fiber for long-haul multi-channel transmission
� 2000- 320 *10Gb/s (12.5 GHz) demonstrated� ...9/11 killed the real ”macho systems”
� 2003 onwards-much more pragmatic approach to whats commercuially feasible
WDM History
© 2006 ADVA Optical Networking. All rights reserved.33
Glass Prism
White Light
Spectrum
School Physics Lesson
© 2006 ADVA Optical Networking. All rights reserved.34
If we have one at each end...
© 2006 ADVA Optical Networking. All rights reserved.35
Optical Wavelengths
400nm
750nm
850nm
1310nm
1550nm
Visible Range
IR 2nd Window
3rd Window
1st Window
UV
DWDM Range1620nm
© 2006 ADVA Optical Networking. All rights reserved.36
CWDM
Transmitter1310 nm
1310 nm1550 nm
Receiver1310 nm
CWDMFilter
CWDMFilter
Transmitter1550 nm
Receiver1550 nm
CWDM filter can be implementedin fiber-optic technology
© 2006 ADVA Optical Networking. All rights reserved.37
Why is CWDM such great ideaWavelength budget
� Standard CWDM filter bandwidth = 13 nm
� Filter bandwidth is allocated between
� Nominal laser wavelength accuracy
� Laser wavelength drift
Filter Bandwidth: 13 nmFilter Bandwidth: 13 nm
Wavelength Accuracy6.5 nm
Wavelength Accuracy6.5 nm
Wavelength drift 6.5 nm
Wavelength drift 6.5 nm
Wavelength budget has implications for laser costWavelength budget has implications for laser cost
© 2006 ADVA Optical Networking. All rights reserved.38
Wavelength drift due to temperature
� DFB laser wavelength drift: 0.1nm/oC
� Laser operating temperature range: -5 to 60oC
� Total wavelength drift: 6.5 nm
� Lasers do not need temperature control
� Eliminates the need for TEC in laser package
Absence of TEC reduces packaging cost & power consumption
Absence of TEC reduces packaging cost & power consumption
© 2006 ADVA Optical Networking. All rights reserved.39
Cost and power savings on CWDM laserscompared to DWDM devices
� Total cost savings on laser: ~ 50 %
� Power savings
� Power consumed by DWDM laser: ~5W
� Power consumed by CWDM laser: ~0.25W
� Consider an 8 channel system
� Power consumed by DWDM lasers: up to 40W
� Power consumed by CWDM lasers: 2W
� But it really only works below 5 GB/s
© 2006 ADVA Optical Networking. All rights reserved.40
DWDM
Example wavelength grid32 ch in C-Band, 32 ch in L-band-OSC signal to control amplifiers at 1630 nm
100 GHz
1,630 nm1,630 nm
OSC
L-Band32 Lambda
(8 Groups with 4 Lambda each)
C-Band32 Lambdas
(8 Groups with 4 Lambda each)
1,550 nm1,550 nm 1,600 nm1,600 nm
notused
Lambdas
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group 7
Group 8
Group 9
Group 10
Group 11
Group 12
Group 13
Group 14
Group 15
Group 16
Note- C-band is always cheaper than L-band
© 2006 ADVA Optical Networking. All rights reserved.41
Multiple SDH vs. DWDM
TxTrans: Transmit Transponder Mux: DWDM MultiplexerRxTrans: Receive Transponder Demux: DWDM DemultiplexerOLA: Optical Line Amplifier LR: SDH Line-Repeater
SDH
... ...
SDH Tx LR LR Rx SDH
SDH Tx LR LR Rx SDH
SDH Tx LR LR Rx SDH
... ...
SDH over DWDM
...
SDH
SDH
SDH Tx TxTrans λj
SDH Tx TxTrans λk
Mu
x
...
SDHRx
SDHRx
SDHRxRxTrans
SDHRxRxTrans
OLATx λ2
Tx λ1
Dem
ux
© 2006 ADVA Optical Networking. All rights reserved.42
� Conversion to ITU-T G.692 wavelength grid in C- and L-Band
� Accepts input at 850, 1310 & 1550 nm (GaAlAs photo diodes)
� Legacy SDH and even PDH equipment can further be used
� All network protocols over same media!!!
Transponders
...
IP Tx TxTrans λj
ATM Tx TxTrans λk
...
PDHRx
SDHRx
IPRxRxTrans
ATMRxRxTrans
SDH Tx TxTrans λ1
PDH Tx TxTrans λ2
Mu
xD
emu
x
RxTrans
© 2006 ADVA Optical Networking. All rights reserved.43
Transponders
2R / 3R Transmit Transponder
CR: Clock Recovery PG: Pulse GeneratorEOM: External Optical Modulator-DisappearingOBPF1: Wavelength Locker-gone for 100GHzCC: Control Circuit OBPF2: Pulse Shaping
CC
CR
PG OBPF2
EOM
OBPF13R only
© 2006 ADVA Optical Networking. All rights reserved.44
SDH / SONET
transparent (2R)
B1 / J0 monitoring
FEC (Coder)
Very-long-haul
Long-haulNon-SDH
transparent (3R)
Short-haul
Long-haul
Input interface Functionality Output interface
Ultra-long-haul
Interoffice
Transmit Transponders
transparent (2R)
Digital Wrapper
transparent (3R)
FEC (Coder)
transparent, multi-clock
© 2006 ADVA Optical Networking. All rights reserved.45
Receive Transponders
SDH / SONET
transparent (2R)
B1 / J0 monitoring
FEC (Decoder)
Long-haul
Non-SDH
transparent (3R)
Long-haul
Input interface Functionality Output interface
transparent (2R)
Digital (De-) Wrapper
transparent (3R)
Very-long-haul
Ultra-long-haul
Short-haul
Interoffice
FEC (Decoder)
transparent, multi-clock
© 2006 ADVA Optical Networking. All rights reserved.46
Filters
� Bragg gratings
� Can be implemented by fiber optics (piece of fiber becomes Bragg grating through UV Laser treatment)
� Temperature sensitive, need control circuit
� Excellent selectivity
� Thin film
� Discrete optics
� Environmentally stable “prisms”
� Good selectivity
� Arrayed Waveguide grating� Can be integrated
� Thin-film technology
� Moderately environmentally stable
© 2006 ADVA Optical Networking. All rights reserved.47
Filter Types
lowlowlowhighdBPDL
very lowvery lowvery lowlowdBNon-adjacent Channel XT
very lowvery lowlowlowdBAdjacent Channel XT
LowlowhighmoderatedBPassband Ripple
HighhighhighmoderatedBSidelobe Suppression
NarrownarrowbroadbroadNmBandwidth
@ -25 dB
BroadbroadbroadnarrowNmBandwidth
@ -0.5 dB
moderatehighlowmoderatedBInsertion
Loss
200 / 100 / 50200 / 100 / 50400 / 200 / 100200 / 100 / 50GHzChannel Spacing
Hybrid Bragg Grating / Filter
Fiber Bragg Grating
Dielectric FiltersArrayed Waveguide Grating
UnitParameter
© 2006 ADVA Optical Networking. All rights reserved.48
Arrayed Waveguide Filter
• Thin-Film waveguide technology• Multiplexing / Demultiplexing by constructive and destructive interference of phase-shifted signals
λ1, λ2, ..., λm λ1λ2
λm
2
1
...m
Input Fiber
Output Fibersm Waveguides with constantLength (Phase) Difference
Phase Shifter
Coupler 1 Coupler 2
© 2006 ADVA Optical Networking. All rights reserved.49
Arrayed Waveguide Filter
Phase Shifter
Output Fibers
Phase Fronts
Focus Point
λ1 λ2 λ3
Wavelength
Atte
nuat
ion
Spectral Characteristic
Channel Selectivity
© 2006 ADVA Optical Networking. All rights reserved.50
DWDM Single-Span
G.692 DWDM Point-to-Point Applications
Single-Span,
long-haul
Single-Span,
very long-haul
Single-Span,
ultra long-haul
Multi-Span,
long-haul
Multi-Span,
very long-haul
1 x 80 km 1 x 120 km 1 x 160 km max. 8 x 80
km
max. 5 x 120
km
BA: Booster Amplifier PA: PreAmplifier
1
n
L < 160 km
Mu
xD
emu
x
1
n
BA PA
... ...
© 2006 ADVA Optical Networking. All rights reserved.51
DWDM Multi-Span
BA: Booster Amplifier OLA: Optical Line Amplifier PA: PreAmplifier
G.692 DWDM Point-to-Point Applications
Single-Span,
long-haul
Single-Span,
very long-haul
Single-Span,
ultra long-haul
Multi-Span,
long-haul
Multi-Span,
very long-haul
1 x 80 km 1 x 120 km 1 x 160 km max. 8 x 80
km
max. 5 x 120
km
1
n
L < 120 km
Mu
xD
emu
x
1
n
BA PAL < 120 kmL < 120 km
OLA OLA
... ...
© 2006 ADVA Optical Networking. All rights reserved.52
DWDM Single-Fiber Working
BA: Booster Amplifier BLA: Bidirectional Line Amplifier PA: PreAmplifier
DWDM Single-Fiber Working can further reduce fiber costs
1
n Mu
x/D
emu
x Mu
x/Dem
ux
1
n
BA PAL < 120 kmL < 120 km
BLA
Fiber Coupler / Band Splitter
... ...
© 2006 ADVA Optical Networking. All rights reserved.53
OADM: Principle
OADM: Optical Add / Drop Multiplexer• Provides Mid-Span access to up to 50% of all wavelengths• Avoids expensive Back-to-Back coupling of optical terminal multiplexers • Currently, wavelengths are selected by fixed-wavelength filters• Next-Generation Flexible OADMs will provide for transparent wavelengths routing
1
n
Mu
xD
emu
x
1
n
BA PA
OLA
OADM
Mu
xD
emu
x
OLA
...
...
© 2006 ADVA Optical Networking. All rights reserved.54
OADM: Fiber Bragg Gratings
Circulator
In Out
λX
λX,Y,ZDrop λX,Y,Z
Add
λY λZ
Fiber Bragg Gratings
• Fiber Bragg Gratings produced by UV Laser radiation
• Circulator is non-reciprocal 3-port
• Alternative: Mach-ZehnderInterferometer (MZI)
• All Add/Drop channels in 1 common fiber
In Out
λXλXDrop λX
Add
λX
MZI
© 2006 ADVA Optical Networking. All rights reserved.55
Substrate
Thin-Film Area
OADM: Thin-Film Technology
• Multiple reflections inside substrate
• Reflection or transmission at thin-film areas
• Add/Drop locations depend on wavelength
• All Add/Drop channels in different fibers
λXDropλX
Add
Out
λZDropλZ
AddIn
λVAdd λV
Drop λYDropλY
Add
© 2006 ADVA Optical Networking. All rights reserved.56
Two-Stage OADM
BS
M
BS
M
Mu
x
Dem
ux
• Split into Band Splitters / Combiners (BSM) and Mux / Demux
• Can decrease insertion loss of OADMs significantly