optical fiber communications optical fiber communications dr. tb. maulana kusuma...
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Optical Fiber CommunicationsOptical Fiber Communications
Dr. Tb. Maulana [email protected]
http://staffsite.gunadarma.ac.id/mkusuma
Magister Teknik Elektro 2006Magister Teknik Elektro 2006
2
Outline
• Introduction
• Optical Fundamentals
• Dense Wavelength Division Multiplexing (DWDM)
Optical Fundamentals
4
• Decibels (dB): unit of level (relative measure) X dB is 10-X/10 in linear dimension e.g. 3 dB Attenuation = 10-.3 = 0.501
Standard logarithmic unit for the ratio of two quantities. In optical fibers, the ratio is power and represents loss or gain.
• Decibels-milliwatt (dBm) : Decibel referenced to a milliwatt X mW is 10log10(X) in dBm, Y dBm is 10Y/10 in mW. 0dBm=1mW, 17dBm = 50mW
• Wavelength (): length of a wave in a particular medium. Common unit: nanometers, 10-9m (nm)
300nm (blue) to 700nm (red) is visible. In fiber optics primarily use 850, 1310, & 1550nm
• Frequency (f): the number of times that a wave is produced within a particular time period. Common unit: TeraHertz, 1012 cycles per second (Thz)
Wavelength x frequency = Speed of light x f = C
Some terminology
5
• Attenuation = loss of power in dB/km The extent to which lighting intensity from the source is diminished as it passes through a given length of fiber-optic (FO) cable, tubing or light pipe. This specification determines how well a product transmits light and how much cable can be properly illuminated by a given light source.
• Chromatic Dispersion = spread of light pulse in ps/nm-km
The separation of light into its different coloured rays.
• ITU Grid = Standard set of wavelengths to be used in optical fiber communications. Unit Ghz, e.g. 400Ghz, 200Ghz, 100Ghz
• Optical Signal to Noise Ration (OSNR) = ratio of optical signal power to noise power for the receiver
• Lambda = name of Greek letter used as wavelength symbol ()
• Optical Supervisory Channel (OSC) = management channel
Some more terminology
6
dB versus dBm
• dBm used for output power and receive sensitivity (Absolute Value)
• dB used for power gain or loss (Relative Value)
7
Bit Error Rate (BER)
• BER is a key objective of the optical system design
• Goal is to get from Tx to Rx with a BER < BER threshold of the Rx
• BER thresholds are on data sheets
• Typical minimum acceptable rate is 10 -12
8
Optical Budget
Optical Budget is affected by: Fiber attenuation
Splices
Patch Panels/Connectors
Optical components (filters, amplifiers, etc)
Bends in fiber
Contamination (dirt/oil on connectors)
Basic Optical Budget = Output Power – Input Sensitivity
Pout = +6 dBm R = -30 dBm
Budget = 36 dB
9
Glass Purity
Propagation Distance Need to Reduce theTransmitted Light Power by 50% (3 dB)
Window Glass 1 inch (~3 cm)
Optical Quality Glass 10 feet (~3 m)
Fiber Optics 9 miles (~14 km)
Fiber Optics Requires Very High Purity Glass
10
AttenuationDispersion
Nonlinearity
Waveform After 1000 KmTransmitted Data Waveform
Distortion
It May Be a Digital Signal, but It’s Analog Transmission
Fiber Fundamentals
11
Attenuation: Reduces power level with distance
Dispersion and Nonlinearities: Erodes clarity with distance and speed
Signal detection and recovery is an analog problem
Analog Transmission Effects
12
CladdingCore
Coating
Fiber Geometry
• An optical fiber is made ofthree sections:
The core carries thelight signals
The cladding keeps the lightin the core
The coating protects the glass
13
n2
n1
Cladding
Core
Intensity Profile
Propagation in Fiber
• Light propagates by total internal reflectionsat the core-cladding interface
• Total internal reflections are lossless
• Each allowed ray is a mode
14
n2
n1
Cladding
Core
n2
n1
Cladding
Core
Different Types of Fiber
• Multi-mode fiberCore diameter varies
50 mm for step index
62.5 mm for graded index
Bit rate-distance product>500 MHz-km
• Single-mode fiberCore diameter is about 9 mm
Bit rate-distance product>100 THz-km
15
• Light
Ultraviolet (UV)
Visible
Infrared (IR)
• Communication wavelengths
850, 1310, 1550 nm
Low-loss wavelengths
• Specialty wavelengths
980, 1480, 1625 nm
UV IR
Visible
850 nm
980 nm1310 nm
1480 nm
1550 nm1625 nm
125 GHz/nm
Wavelength: (nanometers)
Frequency: (terahertz)
C =x
Optical Spectrum
16
Optical Attenuation
• Specified in loss per kilometer (dB/km)
0.40 dB/km at 1310 nm
0.25 dB/km at 1550 nm
• Loss due to absorptionby impurities
1400 nm peak due to OH ions
• EDFA optical amplifiers available in 1550 window
1310Window
1550Window
17T T
P i P0
Optical Attenuation
• Pulse amplitude reduction limits “how far”
• Attenuation in dB
• Power is measured in dBm:
ExamplesExamples
10dBm10dBm 10 mW10 mW
0 dBM0 dBM 1 mW1 mW
-3 dBm-3 dBm 500 uW500 uW
-10 dBm-10 dBm 100 uW100 uW
-30 dBm-30 dBm 1 uW1 uW
)
18
• Polarization Mode Dispersion (PMD) Single-mode fiber supports two polarization
states
Fast and slow axes have different group velocities
Causes spreading of the light pulse
• Chromatic Dispersion Different wavelengths travel at different speeds
Causes spreading of the light pulse
Types of Dispersion
19
• Affects single channel and DWDM systems
• A pulse spreads as it travels down the fiber
• Inter-symbol Interference (ISI) leads to performance impairments
• Degradation depends on:
laser used (spectral width)
bit-rate (temporal pulse separation)
Different SM types
Interference
A Snapshot on Chromatic Dispersion
20
60 Km SMF-28
4 Km SMF-28
10 Gbps
40 Gbps
Limitations From Chromatic Dispersion
t
t
• Dispersion causes pulse distortion, pulse "smearing" effects
• Higher bit-rates and shorter pulses are less robust to Chromatic Dispersion
• Limits "how fast“ and “how far”
21
Combating Chromatic Dispersion
• Use DSF and NZDSF fibers
(G.653 & G.655)
• Dispersion Compensating Fiber
• Transmitters with narrow spectral width
22
Dispersion Compensating Fiber
• Dispersion Compensating Fiber:
By joining fibers with CD of opposite signs (polarity) and suitable lengths an average dispersion close to zero can be obtained; the compensating fiber can be several kilometers and the reel can be inserted at any point in the link, at the receiver or at the transmitter
23
Dispersion Compensation
Transmitter
Dispersion Compensators
Dispersion Shifted Fiber Cable
+1000
-100-200-300-400-500
Cu
mu
lati
ve D
isp
ersi
on
(p
s/n
m)
Total Dispersion Controlled
Distance fromTransmitter (km)
No CompensationWith Compensation
24
How Far Can I Go Without Dispersion?
Distance (Km) =Specification of Transponder (ps/nm)
Coefficient of Dispersion of Fiber (ps/nm*km)
A laser signal with dispersion tolerance of 3400 ps/nm
is sent across a standard SMF fiber which has a Coefficient of Dispersion of 17 ps/nm*km.
It will reach 200 Km at maximum bandwidth.Note that lower speeds will travel farther.
25
Polarization Mode Dispersion
• Caused by ovality of core due to:
Manufacturing process
Internal stress (cabling)
External stress (trucks)
• Only discovered inthe 90s
• Most older fiber not characterized for PMD
26
Polarization Mode Dispersion (PMD)
• The optical pulse tends to broaden as it travels down the fiber; this is a much weaker phenomenon than chromatic dispersion and it is of little relevance at bit rates of 10Gb/s or less
nx
nyEx
Ey
Pulse As It Enters the Fiber Spreaded Pulse As It Leaves the Fiber
27
Combating Polarization Mode Dispersion
• Factors contributing to PMDBit Rate
Fiber core symmetry
Environmental factors
Bends/stress in fiber
Imperfections in fiber
• Solutions for PMDImproved fibers
Regeneration
Follow manufacturer’s recommended installation techniques for the fiber cable
28
• SMF-28(e) (standard, 1310 nm optimized, G.652)
Most widely deployed so far, introduced in 1986, cheapest
• DSF (Dispersion Shifted, G.653)
Intended for single channel operation at 1550 nm
• NZDSF (Non-Zero Dispersion Shifted, G.655)
For WDM operation, optimized for 1550 nm region
– TrueWave, FreeLight, LEAF, TeraLight…
Latest generation fibers developed in mid 90’s
For better performance with high capacity DWDM systems
– MetroCor, WideLight…
– Low PMD ULH fibers
Types of Single-Mode Fiber
29The primary Difference is in the Chromatic Dispersion Characteristics
Different Solutions for Different Fiber Types
SMF
(G.652)
•Good for TDM at 1310 nm
•OK for TDM at 1550
•OK for DWDM (With Dispersion Mgmt)
DSF
(G.653)
•OK for TDM at 1310 nm
•Good for TDM at 1550 nm
•Bad for DWDM (C-Band)
NZDSF
(G.655)
•OK for TDM at 1310 nm
•Good for TDM at 1550 nm
•Good for DWDM (C + L Bands)
Extended Band
(G.652.C)
(suppressed attenuation in the traditional water peak region)
•Good for TDM at 1310 nm
•OK for TDM at 1550 nm
•OK for DWDM (With Dispersion Mgmt
•Good for CWDM (>8 wavelengths)
DWDM
31
Outline
• Introduction
• Components
• Forward Error Correction
• DWDM Design
• Summary
32
Increasing Network Capacity Options
Faster Electronics(TDM)
Higher bit rate, same fiberElectronics more expensive
More Fibers(SDM)
Same bit rate, more fibersSlow Time to MarketExpensive EngineeringLimited Rights of WayDuct Exhaust
WDM
Same fiber & bit rate, more sFiber CompatibilityFiber Capacity ReleaseFast Time to MarketLower Cost of OwnershipUtilizes existing TDM Equipment
33
Single Single Fiber (One Fiber (One
Wavelength)Wavelength)
Channel 1
Channel n
Single FiberSingle Fiber(Multiple (Multiple
Wavelengths)Wavelengths)
l1l1
l2l2
lnln
Fiber Networks
• Time division multiplexingSingle wavelength per fiber
Multiple channels per fiber
4 OC-3 channels in OC-12
4 OC-12 channels in OC-48
16 OC-3 channels in OC-48
• Wave division multiplexingMultiple wavelengths per fiber
4, 16, 32, 64 channels per system
Multiple channels per fiber
34
Types of WDM
• Coarse WDM (CWDM)Uses 3000GHz (20 nm) spacing.
Up to 18 channels.
Distance of 50 km on a single mode fiber.
• Dense WDM (DWDM)Uses 200, 100, 50, or 25 GHz spacing.
Up to 128 or more channels.
Distance of several thousand kilometres with amplification and regeneration.
35
DS-1DS-1DS-3DS-3OC-1OC-1OC-3OC-3
OC-12OC-12OC-48OC-48
OC-12cOC-12cOC-48cOC-48c
OC-192cOC-192c
FiberFiber
DWDMDWDMOADMOADM
SONETSONETADMADM
FiberFiber
TDM and DWDM Comparison
• TDM (SONET/SDH)
Takes sync and async signals and multiplexes them to a single higher optical bit rate
E/O or O/E/O conversion
• (D)WDM
Takes multiple optical signals and multiplexes onto a single fiber
No signal format conversion
36
DWDM History
• Early WDM (late 80s)Two widely separated wavelengths (1310, 1550nm)
• “Second generation” WDM (early 90s)Two to eight channels in 1550 nm window
400+ GHz spacing
• DWDM systems (mid 90s)16 to 40 channels in 1550 nm window
100 to 200 GHz spacing
• Next generation DWDM systems64 to 160 channels in 1550 nm window
50 and 25 GHz spacing
37
TERMTERM
TERM
Conventional TDM Transmission—10 Gbps
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
TERM
40km
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
TERM1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
TERM1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
TERM
120 km
OC-48
OA OAOA OA120 km 120 km
OC-48OC-48
OC-48
OC-48OC-48
OC-48OC-48
DWDM Transmission—10 Gbps
1 Fiber Pair4 Optical Amplifiers
Why DWDM—The Business Case
TERM
4 Fibers Pairs 32 Regenerators
40km 40km 40km 40km 40km 40km 40km 40km
38
Drivers of WDM Economics
• Fiber underground/undersea
Existing fiber
• Conduit rights-of-way
Lease or purchase
• Digging
Time-consuming, labor intensive, license
$15,000 to $90,000 per Km
• 3R regenerators
Space, power, OPS in POP
Re-shape, re-time and re-amplify
• Simpler network management
Delayering, less complexity, less elements
39
• Transparency
Can carry multiple protocols on same fiber
Monitoring can be aware of multiple protocols
• Wavelength spacing 50GHz, 100GHz, 200GHz
Defines how many and which wavelengths can be used
• Wavelength capacity Example: 1.25Gb/s, 2.5Gb/s, 10Gb/s
0 50 100 150 200 250 300 350 400
Characteristics of a WDM NetworkWavelength Characteristics
40
Optical Transmission Bands
Band Wavelength (nm)
820 - 900
1260 – 1360
“New Band” 1360 – 1460
S-Band 1460 – 1530
C-Band 1530 – 1565
L-Band 1565 – 1625
U-Band 1625 – 1675
41
ITU Wavelength Grid
• ITU-T grid is based on 191.7 THz + 100 GHz
• It is a standard for laser in DWDM systems
1530.33 nm 1553.86 nm
0.80 nm
195.9 THz 193.0 THz100 GHz
Freq (THz) ITU Ch Wave (nm) 15201/252 15216 15800 15540 15454192.90 29 1554.13 x x x x x192.85 1554.54192.80 28 1554.94 x x x x x192.75 1555.34192.70 27 1555.75 x x x x x192.65 1556.15192.60 26 1556.55 x x x x x
42
800 900 1000 1100 1200 1300 1400 1500 1600
Wavelength in Nanometers (nm)
0.2 dB/Km
0.5 dB/Km
2.0 dB/Km
Attenuation vs. WavelengthAttenuation vs. Wavelength S-Band:1460–1530nm
L-Band:1565–1625nm
C-Band:1530–1565nm
Fiber Attenuation Characteristics
Fibre Attenuation Curve
43
Ability to put multiple services onto a single wavelength
Characteristics of a WDM NetworkSub-wavelength Multiplexing or MuxPonding
44
Why DWDM?The Technical Argument
• DWDM provides enormous amounts of scaleable transmission capacity
Unconstrained by speed ofavailable electronics
Subject to relaxed dispersion and nonlinearity tolerances
Capable of graceful capacity growth
45
Outline
• Introduction
• Components
• Forward Error Correction
• DWDM Design
46
Optical Multiplexer
Optical De-multiplexer
Optical Add/Drop Multiplexer(OADM)
Transponder(Transmitter-responder)
DWDM Components
1
2
3
1
2
3
15xx
1
2
3
1...n
1...n
47
Transponders
• Converts broadband optical signals to a specific wavelength via optical to electrical to optical conversion (O-E-O)
• Used when Optical LTE (Line Termination Equipment) does not have tight tolerance ITU optics
• Performs 2R or 3R regeneration function
• Receive Transponders perform reverse function
Low Cost IR/SR Optics
Wavelengths Converted
1
From Optical OLTE
To DWDM MuxOEO
OEO
OEO
2
n
48
Optical Amplifier(EDFA)
Optical AttenuatorVariable Optical Attenuator
Dispersion Compensator (DCM / DCU)
More DWDM Components
49
VOA EDFA DCM
VOAEDFADCM
Service Mux(Muxponder)
Service Mux(Muxponder)
DWDM SYSTEM DWDM SYSTEM
Typical DWDM Network Architecture
50
Performance Monitoring
• Performance monitoring performed on a per wavelength basis through transponder
• No modification of overhead
Data transparency is preserved
51
Laser Characteristics
cPower
Power c
DWDM Laser Distributed Feedback (DFB)
Active medium
MirrorPartially transmitting
Mirror
Amplified light
Non DWDM Laser Fabry Perot
• Spectrally broad
• Unstable center/peak wavelength
• Dominant single laser line
• Tighter wavelength control
52
DWDM Receiver Requirements
• Receivers Common to all Transponders
• Not Specific to wavelength (Broadband)
I
53
Optical Amplifier
Pout = GPinPin
• EDFA amplifiers
• Separate amplifiers for C-band and L-band
• Source of optical noise
• Simple
• Co-directional (pumping) and Counter-directional
GG
54
OA Gain
TypicalFiber Loss
4 THz
25 THz
OA Gain and Fiber Loss
• OA gain is centered in 1550 window
• OA bandwidth is less than fiber bandwidth
55
Erbium Doped Fiber Amplifier
“Simple” device consisting of four parts:
• Erbium-doped fiber
• An optical pump (to invert the population).
• A coupler
• An isolator to cut off backpropagating noise
Isolator Coupler IsolatorCoupler
Erbium-DopedFiber (10–50m)
PumpLaserPumpLaser
PumpLaserPumpLaser
56
Optical Signal-to Noise Ratio (OSNR)
• Depends on :
Optical Amplifier Noise Figure:
(OSNR)in = (OSNR)outNF
• Target : Large Value for X
Signal Level
Noise Level
X dB
EDFA SchematicEDFA Schematic
(OSNR)out(OSNR)in
NFPin
57
Loss Management: LimitationsErbium Doped Fiber Amplifier
• Each amplifier adds noise, thus the optical SNR decreases gradually along the chain; we can only have a finite number of amplifiers and spans and eventually electrical regeneration will be necessary
• Gain flatness is another key parameter mainly for long amplifier chains
Each EDFA at the Output Cuts at Least in a Half (3dB) the OSNR Received at the Input
Noise Figure > 3 dBTypically between 4 and 6
Noise Figure > 3 dBTypically between 4 and 6
58
n
n
Dielectric Filter
• Well established technology, up to 200 layers
Optical Filter Technology
59
Multiplexer / Demultiplexer
Wavelengths Converted via Transponders
Wavelength Multiplexed Signals
DWDMMux DWDM
Demux
Wavelength Multiplexed Signals
Wavelengths separated into individual ITU Specific lambdas
Loss of power for each Lambda
60
Optical Add/Drop Filters (OADMs)
OADMs allow flexible add/drop of channels
Drop Channel
Add Channel
Drop & Insert
Pass Through loss and Add/Drop loss
61
Optical Multiplexing Filter
• Thin-film filters.
• Bragg gratings.
• Arrayed waveguide gratings (AWGs).
• Periodic filters, frequency slicers, interleavers.
62
Thin-film Filter
• The thin-film filter (TFF) is a device used in some optical networks to multiplex and demultiplex optical signals.
• Use many ultra-thin layers of dielectric material coating deposited on a glass or polymer substrate.
• This substrate can be made to let only photons of a specific wavelength pass through, while all others are reflected.
• By integrating a number of these components, several wavelengths can be demultiplexed.
63
Bragg Gratings
• A Bragg Grating is made of a small section of fiber that has been modified by exposure to ultraviolet radiation to create periodic changes in the refractive index of the fiber.
• Light travelling through the Bragg Grating is refracted and then reflected back slightly, usually occurring at one particular wavelength.
• The reflected wavelength, known as the Bragg resonance wavelength, depends on the amount of refractive index change that has been applied to the Bragg grating fiber and this also depends on how distantly spaced these changes to refraction are.
64
Arrayed Waveguides
• In the transmit direction, the AWG mixes individual wavelengths, also called lambdas (λ) from different lines etched into the AWG substrate (the base material that supports the waveguides) into one etched line called the output waveguide, thereby acting as a multiplexer.
• In the opposite direction, the AWG can demultiplex the composite λs onto individual etched lines.
• Usually one AWG is for transmit and a second one is for receive.
65
Periodic Filters, Frequency Slicers, Interleavers
• Periodic filters, frequency slicers, and interleavers are devices that can share the same functions and are usually used together.
• Stage 1 is a kind of periodic filter, an AWG.
• Stage 2 is representative of a frequency slicer on its input, in this instance, another AWG; and an interleaver function on the output, provided by six Bragg gratings.
• Six λs are received at the input to the AWG, which then breaks the signal down into odd λ and even λ.
• The odd λs and even λs go to their respective stage 2 frequency slicers and then are delivered by the interleaver in the form of six discrete interference-free optical channels for end customer use.
66
Outline
• Introduction
• Components
• Forward Error Correction
• DWDM Design
• Summary
67
Transmission Errors
• Errors happen!
• An old problem of our era (PCs, wireless…)
• Bursty appearance rather than distributed
• Noisy medium (ASE, distortion, PMD…)
• TX/RX instability (spikes, current surges…)
• Detect is good, correct is better
Transmitter ReceiverTransmission
Channel
Information InformationNoise
68
Error Correction
• Error correcting codes both detect errors and correct them
• Forward Error Correction (FEC) is a system
adds additional information to the data stream
corrects eventual errors that are caused by the transmission system.
• Low BER achievable on noisy medium
69
FEC Performance, Theoretical
Received Opticalpower (dBm)
Bit Error Rate
10-30
10-10
-46 -44 -42 -40 -38
1
10-20
-36 -34 -32
BER without FEC
BER with FEC
Coding Gain
BER floor
FEC gain 6.3 dB @ 10-15 BER
70
FEC in DWDM Systems
• FEC implemented on transponders (TX, RX, 3R)
• No change on the rest of the system
IP
SDH
ATM
.
.
FEC
FEC
FEC
2.48 G 2.66 G
9.58 G 10.66 G
IP
SDH
ATM
.
.
FEC
FEC
FEC
2.66 G 2.48 G
10.66 G 9.58 G
71
Outline
• Introduction
• Components
• Forward Error Correction
• DWDM Design
• Summary
72
DWDM Design Topics
• DWDM Challenges
• Unidirectional vs. Bidirectional
• Protection
• Capacity
• Distance
73
Transmission Effects
• Attenuation:
Reduces power level with distance
• Dispersion and nonlinear effects:
Erodes clarity with distance and speed
• Noise and Jitter:
Leading to a blurred image
74
OA
Solution for Attenuation
LossLossOptical
AmplificationOptical
Amplification
75
Solution For Chromatic Dispersion
Length
Dispersion
+D -D
DispersionDispersion Saw ToothCompensationSaw ToothCompensation
Total dispersion averages to ~ zero
Fiber spool Fiber spoolDCU DCU
76
Uni Versus Bi-directional DWDM
DWDM systems can be implemented in two different ways
Bi -directional
Fiber
Uni -directional
Fiber
Fiber
• Uni-directional:
wavelengths for one direction travel within one fiber
two fibers needed for
full-duplex system
• Bi-directional:
a group of wavelengths for each direction
single fiber operation for full-duplex system
77
Uni Versus Bi-directional DWDM (cont.)
32
32
Full band
Full band
ChannelSpacing100 GHz
16
16
Blue-band
Red-band
ChannelSpacing100 GHz
16
16
• Uni-directional 32 channels system
• Bi-directional 32 channels system
32 chfull
duplex
16 chfull
duplex
78
DWDM Protection Review
Y-Cable and Line CardProtected
Client ProtectedUnprotected
Splitter Protected
79
1 Transponder
1 ClientInterface
• 1 client & 1 trunk laser (one transponder) needed, only 1 path available
• No protection in case of fiber cut, transponder failure, client failure, etc..
Unprotected
80
2 Transponders
2 Clientinterfaces
• 2 client & 2 trunk lasers (two transponders) needed, two optically unprotected paths
• Protection via higher layer protocol
Client Protected Mode
81
• Only 1 client & 1 trunk laser (single transponder) needed
• Protects against Fiber Breaks
Optical Splitter Switch
Workinglambda
protectedlambda
Optical Splitter Protection
82
• 2 client & 2 trunk lasers (two transponders) needed
• Increased cost & availability
2 Transponders
Only oneTX active
workinglambda
protectedlambda
“Y” cable
Line Card / Y- Cable Protection
83
Wavelengths
Bit
Ra
te
Distance
SolutionSpace
Designing for Capacity
• Goal is to maximize transmission capacity and system reach
Figure of merit is Gbps • Km
Long-haul systems push the envelope
Metro systems are considerably simpler
84
Designing for Distance
Amplifier Spacing
G = Gain of AmplifierS
Pout
Pnoise
Pin
D = Link Distance
L = Fiber Loss in a Span
• Link distance (D) is limited by the minimum acceptable electrical SNR at the receiverDispersion, Jitter, or optical SNR can be limit
• Amplifier spacing (S) is set by span loss (L)Closer spacing maximizes link distance (D)
Economics dictates maximum hut spacing
85
Link Distance vs. OA Spacing
2.5
5
10
20
2000 4000 6000 80000
Total System Length (km)
Wav
elen
gth
Cap
acit
y (G
b/s
) Amp Spacing60 km
80 km
100 km
120 km
140 km
• System cost and and link distance both depend strongly on OA spacing
86
OEO Regeneration in DWDM Networks
Long Haul
• OA noise and fiber dispersion limit total distance before regenerationOptical-Electrical-Optical conversionFull 3R functionality: Reamplify, Reshape, Retime
• Longer spans can be supported using back to back systems
87
• Express channels must be regenerated
• Two complete DWDM terminals needed
• Provides drop-and- continue functionality
• Express channels only amplified, not regenerated
• Reduces size, powerand cost
Back-to-back DWDM
Optical add/drop multiplexer
7
1234
N
OADM
7
1234
N
7
1234
N7
1234
N
3R with Optical Multiplexer and OADM
88
Outline
• Introduction
• Components
• Forward Error Correction
• DWDM Design
• Summary
89
DWDM Benefits
• DWDM provides hundreds of Gbps of scalable transmission capacity today
Provides capacity beyondTDM’s capability
Supports incremental, modular growth
Transport foundation for nextgeneration networks
90
Metro DWDM
• Metro DWDM is an emerging market for next generation DWDM equipment
• The value proposition is very different from the long haul
Rapid-service provisioning
Protocol/bitrate transparency
Carrier Class Optical Protection
• Metro DWDM is not yet as widely deployed