opt-1101(usa2006) - optical fundamentals
DESCRIPTION
.TRANSCRIPT
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1 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Fundamentals
OPT-1101
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2 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Agenda
Introduction and Terminology
Optical Propagation and Fiber Characteristics
Attenuation and Compensation
Dispersion and Dispersion Compensation
Non Linearity
SM Optical Fiber Types
Simple SPAN Design
Summary
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3 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Introduction
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4 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Modern Lightwave Eras
0
1
10
100
1,000
10,000
1985 1990 1995 2000Year
C
a
p
a
c
i
t
y
(
G
b
/
s
)
FiberizationDigitization
SONET Rings and DWDM Linear Systems
Optical NetworkingWavelength Switching
Research Systems
Commercial Systems
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5 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Spectrum
LightUltraviolet (UV)VisibleInfrared (IR)
Communication wavelengths
850, 1310, 1550 nmLow-loss wavelengths
Specialty wavelengths980, 1480, 1625 nm
UV IR
Visible
850 nm980 nm
1,310 nm1,480 nm
1,550 nm1,625 nm
125 GHz/nm
Wavelength: (Nanometers)Frequency: (Nerahertz)
C = x
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6 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Terminology
Decibels (dB): unit of level (relative measure) X dB is 10X/10
Decibels-milliwatt (dBm): decibel referenced to a milliwatt
dBm used for output power and receive sensitivity (absolute value)dB used for power gain or loss (relative value)X mW is 10log10(X) in dBm, Y dBm is 10Y/10 in mW
Wavelength (Lambda): length of a wave in a particular medium; common unit: nanometers, 109m (nm)
Frequency (): the number of times that a wave is produced within a particular time period
Wavelength x frequency = speed of light x = C
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7 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
TerminologyFiber Impairments
Attenuation = Loss of power in dB/km
Chromatic Dispersion = Spread of light pulse in ps/nm-km
Optical Signal-to-Noise Ratio (OSNR) = Ratio of optical signal power to noise power for the receiver
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8 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
ITU Wavelength Grid
The International Telecommunications Union (ITU) has divided thetelecom wavelengths into a grid; the grid is divided into bands;the C and L bands are typically used for DWDM
ITU Bands
1530.33 nm 1553.86 nm0.80 nm
195.9 THz 193.0 THzChannel Spacing = 100 GHz
O E S C L U (nm)
0 1 n
1
2
6
0
1
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6
0
1
4
6
0
1
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9 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Bit Error Rate (BER)
BER is a key objective of the optical system designBER = P(1)P(0 received for 1 transmitted) + P(0)P(1 received for 0 transmitted)
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 1012
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10 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Eye Diagram
An eye diagram shows a relative performance of the signal The opening of the eye provides valuable information about
the ability of the receiver to detect the signal correctly
Consider All Eight Possible Combination of 3-Bit Sequence
Superimpose All CombinationsEye Pattern
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11 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Eye Diagram
The vertical eye opening shows the ability to distinguish between a 1 and a 0 bit
The horizontal opening gives the time period over which the signal can be sampled without errors
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12 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Eye Diagram
For a good transmission system, the eye opening should be as wide and open as possible
Eye diagram also displays information such as maximum signal voltage, rise and decay time of pulse, etc.
Extinction ratio (ratio of a 1 signal to a 0 signal) is also calculated from eye diagram
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13 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Eye Mask Testing
It is difficult to measure a numeric value that can describe the openness of the eye
A process called eye-mask testing is used
Eye Mask is a collection of polygons that represents where the eye waveform cannot exist
Eye diagram is not allowed to cross or intersect the mask
Minimum acceptable opening is defined by the shape and size of polygon
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14 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Power
Optical Power Measurements: Power is measured in watts; however, a convenient way to
measure optical power is in units of decibels (dB)
The power measured on a particular signal is measured in dBm
The gain/loss measured between two points on a fiber is in dBPower loss is expressed as negative dB
Power gain is expressed as positive dB
Definition: Optical Power Is the Rate at Which
Power Is Delivered in an Optical Beam
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15 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Power Budget
Calculate using minimum transmitter power and minimum receiver sensitivity
Attenuation/loss in the link, greater than the power budget, causes bit errors (dB)
Allow for two to three dBm power loss budget; so if the power budget is 15 dB, design for 12
Design networks with power budgets, not distances
The Optical Power Budget is:Optical Power Budget = Power Sent Receiver Sensitivity
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16 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Power BudgetExample
Transmitter maximum power = 2 dBm Receiver sensitivity = 28 dBm
2 dBm 28 dBmTransmitter Receiver
Power Budget = 26 dB
Common Power Budgets
Short Reach (SR) 6 dB (75% Power Loss)
Intermediate Reach (IR) 13 dB (95% Power Loss
Long Reach (LR) 26 dB (99.75% Power Loss)
Calculate Power Budget = ??
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17 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
A Few Words on Optical Safety
Think optical safety at all times
Optical power is invisible to the human eye
Never stare at an optical connector
Keep optical connectors pointed away from yourself and others
Glass (fiber cable) can cut and puncture
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18 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Laser Classifications/Safety IconsClass 1Lasers that are incapable of causing damage when the beam is directed into the eye under normal operating conditions. These include helium-neon lasers operating at less than a few microwatts of radiant power.
Class 2Lasers that can cause harm if viewed directly for second or longer. This includes helium-neon lasers with an output up to 1 mW (milliwatt).
Class 3ALasers that have outputs less than 5 mW. These lasers can cause injury when the eye is exposed to either the beam or its reflections from mirrors or other shiny surfaces. As an example, laser pointers typically fall into this class.
Class 3BLasers that have outputs of 5 to 500 mW. The argon lasers typically used in laser light shows are of this class. Higher power diode lasers (above 5 mW) from optical drives and high performance laser printers also fall into this class.
Class 4Lasers that have outputs exceeding 500 mW. These devices produce a beam that is hazardous directly or from reflection and can produce skin burn. Many ruby, carbon dioxide, and neodymium-glass lasers are class 4.
SR and IR Optics, Some LR
Many LR Optics, CWDM GBICS
Some LR Optics, Amplifier Outputs
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19 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Protective Eyewear Available
Protective goggles or glasses should be worn for all routine use of Class 3B and Class 4 lasers
Remember: eyewear is wavelength specific, a pair of goggles that effectively blocks red laser light affords no protection for greenlaser light
Laser Safety Equipment Can Be Investigated in Greater Detail at the
Following Link:http://www.lasersafety.co.uk/frhome.html
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20 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Some Final Words on Optical Equipment Safety
Remember: Optical cabling is constructed from strands of glass, about the size of a human hair. Never handle exposed fiber strands unless you have the proper training. Fiber fragments that becomeembedded under the skin can be extremely painful, and are very difficult (in some cases impossible) to remove.
Remember: Optical equipment is typically powered from either 120vac or 48vdc. Always remove jewelry such as rings, watches, bracelets, etc. when working with energized equipment. Care should be taken to never come in contact with exposed electrical connections or buswork.
Remember: Be careful not to damage equipment through ESD (Electrostatic Discharge). Ensure that all equipment is properlygrounded, wrist straps are used when removing modules with active components and always handle equipment modules by their edges.
Note: Many Companies Have Documented ESD Guidelines to Their Environment. Please Consult Those Documents for Additional Detail as Appropriate.
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21 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical Propagation in Fibers
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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
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23 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Fiber Geometry
The core carries thelight signals
The cladding keeps the lightin the core
The coating protects the glass
Coating
An Optical Fiber Is Made of Three Sections:
CladdingCore
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24 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Fiber Dimensions
Fiber dimensions are measured in m
1 m = 0.000001 meters (10-6)
1 human hair ~ 50 m
Refractive Index (n)n = c/v
n ~ 1.46
n (core) > n (cladding)
Cladding(125 m)
Core(245 m)
Coating(862.5 m)
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25 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Geometrical Optics
1 = Angle of incidence 1r = Angle of reflection 2 = Angle of refraction 1 1r
2n2n1
cIs the Critical AngleIf Angle of Incidence Is Greater Than Critical Angle, All the Light Will Reflect (Instead of Refract); This Is Called Total Internal Reflection
c
2=90
n2
>
n1
n1 n2
c>
Light Is Reflected/Refracted at an Interface
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26 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Propagation in Fiber
Light propagates by total internal reflectionsat the core-cladding interface
Total internal reflections are lossless
Each allowed ray is a mode
1
n2
n1
Cladding
0 CoreIntensity Profile
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27 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
n2
n1
Cladding
Core
n2
n1
Cladding
Core
Different Types of Fiber
Multimode 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
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28 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Attenuation
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29 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Attenuation in Fiber
Light loss in fiber is caused by two thingsAbsorption by the fiber material
Scattering of the light from the fiber
Light loss causes signal attenuation
Rayleigh Scattering
Scattering
850 nm Highest
1310 nm Lower
1550 nm Lowest
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30 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Other Causes of Attenuation in Fiber
MicrobendsCaused by small distortions of the fiber in manufacturing
MacrobendsCaused by wrapping fiber around a corner with too small a bending radius
Back reflectionsCaused by reflections at fiber ends, like connectors
Fiber splicesCaused by poor alignment or dirt
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31 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
T T
Pi P0
Optical Attenuation
Pulse amplitude reduction limits how far
Attenuation in dB=10xLog(Pi/Po) Power is measured in dBm:
P(dBm)=10xlog(P mW/1 mW)
Examples
10 dBm 10 mW0 dBM 1 mW
3 dBm 500 uW10 dBm 100 uW30 dBm 1 uW
)
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32 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Attenuation Response at Different Wavelengths
850nm Region 1310 nm Region 1550 nm Region
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33 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Attenuation: Compensated by Optical Amplifiers
Erbium-doped fiber amplifiers (EDFA) are the most commonly deployed optical amplifiers
Commercially available since the early 1990sWorks best in the range 1530 to 1565 nmGain up to 30 dB (1000 photons out per photon in)
Optically transparentWavelength transparentBit rate transparent
Input
1480 or 980 nm Pump Laser
Erbium Doped Fiber
Output
IsolatorCoupler
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34 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Energy = h .
Fundamental State
Excited State
Pump Photonat 980 nm
Fundamental State
Transition to a Lower Energy StateMetastable State
Telecom SignalPhoton at 1550 nm
Energy = h .
Einstein Tells Us That the Photon Generated by the Decay of the
Erbuim Ion Back to Its Fundamental State Will Be the Same Phase as the
Signal Photon that Triggered the Stimulated Emission
+ =Amplified Telecom
SignalPhoton at 1550 nm
The Photoelectric Effect in Erbium
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35 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Dispersion
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36 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Types of Dispersion
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
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37 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
A Snapshot on Chromatic Dispersion
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
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38 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
60 Km SMF-28
10 Gbps
t
40 Gbps
t
Limitations from Chromatic Dispersion
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
4 Km SMF-28
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39 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Combating Chromatic Dispersion
Use DSF and NZDSF fibers(G.653 and G.655)
Dispersion compensating fiber
Transmitters with narrow spectral width
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40 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Industry StandardNot Cisco Specific
Transmission Over SM FiberWithout Compensation
Transmission Rate Distance
2.5 Gb/s 980 km
10 Gb/s 60 km
40 Gb/s 4 km
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41 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
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 SM 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
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42 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Dispersion Compensation
Dispersion Shifted Fiber Cable
+1000
100200300400500
Distance from Transmitter (km)
No CompensationWith Compensation
Transmitter
Dispersion Compensators
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Total Dispersion Controlled
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43 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Polarization Mode Dispersion
Caused by ovality of core due to:Manufacturing process Internal stress (cabling) External stress (trucks)
Only discovered in the 90s Most older fiber not characterized for PMD
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44 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
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 some relevance at bit rates of 10Gb/s or more
nx
nyEx
Ey
Pulse as It Enters the Fiber Spreaded Pulse as It Leaves the Fiber
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45 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Combating Polarization Mode Dispersion
Factors contributing to PMDBit rateFiber core symmetryEnvironmental factorsBends/stress in fiberImperfections in fiber
Solutions for PMDImproved fibers RegenerationFollow manufacturers recommended installation techniques for the fiber cable
PMD does not need compensation up to 10G in systems up to about 1600km optical transmission, while compensation is required for longer systems or 40G
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46 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Nonlinearity
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47 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
From Linear to Non-Linear Propagation
As long as optical power within an optical fiber is small, the fiber can be treated as a linear medium
Loss and refractive index are independent of the signal power
When optical power levels gets fairly high, the fiber becomes a nonlinear medium
Loss and refractive index depend on the optical power
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48 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Effects of Nonlinearity Self-Phased Modulation (SPM) and Cross Phase Modulation (XPM)
Interference
Interference
Multiple Channels Interact as They Travel (XPM)
A Single Channels Pulses Are Self-Distorted as They Travel (SPM)
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49 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Out of Fiber1 221-2 22-11 2
Into Fiber
Four-Wave Mixing (FWM)
Channels beat against each other to form intermodulation products
Creates in-band crosstalk that cannot be filtered (optically or electrically)
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50 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Four-Wave Mixing (FWM)
If you have dispersion the beat signal will not fall on a real signal
Hence some dispersion is really good
Dispersion (some) helps to prevent FWM
Out of Fiber1 2 22-11 2
Into Fiber21-2
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51 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Channel Spacing (nm)
0.0 0.5 1.0 1.5 2.0 2.550
30
10
0
20
40
D=0
D=17
D=2
D=0.2
FWM and Dispersion
F
W
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f
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d
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Dispersion Washes Out FWM Effects
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52 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Re-Shape DCU
The Three Rs of Optical Networking
Pulse as It Enters the Fiber Pulse as It Exits the Fiber
Re-Gen to Boost the Power
tts Optimum Sampling Time
tts Optimum Sampling Time
Phase Variation
Re-TimeO-E-O
Re-gen, Re-Shape, andRemove Optical Noise
tts Optimum Sampling Time
Phase Re-Alignment*
*Simplification
The Options to Recover the Signal from Attenuation/Dispersion/Jitter Degradation Are:
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53 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
SM Optical Fiber Types
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54 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Types of Single-Mode Fiber
SMF (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)LS
For WDM operation in the 1550 nm region onlyTrueWave, FreeLight, LEAF, TeraLight, etc.
Latest generation fibers developed in mid 90sFor better performance with high capacity DWDM systems
MetroCor, WideLight
Low PMD ultra long haul fibers
TrueWave Is a Trademark of Lucent; TeraLight Is a Trademark of Alcatel; FreeLight and WideLight Are Trademarks of Pirelli; MetroCor Is a Trademark of Corning
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55 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Fiber Dispersion Characteristics
Normal fiber Non-Dispersion Shifted Fiber (NDSF) G.652 > 90% of deployed plant
20
15
10
5
0
5
10
15
20
25
1350 1370 1390 1410 1430 1450 1470 1490 1510 1530 1550 1570 1590 1610 1630 1650
DS NZDS+NZDS- SMF
Wavelength (in nm)
D
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DSF G.653NZDSF G.655
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56 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
The 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 (> Eight wavelengths)
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57 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
SPAN Design
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Span Design LimitsAttenuation
Source and receiver characteristicsTx: 0dBmRx sensitivity: 28dBm Dispersion tolerance: 1600ps/nmOSNR requirements: 21dB
Span characteristicsDistance: 120kmSpan loss: .25dB/km (30dB total)Dispersion: 18ps/nm*km
Tx
Rx
Time Do
main 0dBm
Wavelen
gth
Domain
20km
5dBm
25dBm
100km
30dBm
120km
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59 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Span Design LimitsAmplification
Source and receiver characteristicsTx: 0dBmRx sensitivity: 28dBm Dispersion tolerance: 1600ps/nmOSNR requirements: 21dB
Span characteristicsDistance: 120kmSpan loss: .25dB/km (30dB total)Dispersion: 18ps/nm*km
Tx
Rx
Time Do
main
+12dBm
20km
8dBm
100km
Wavelen
gth
Domain
13dBm
120km
EDFA
-6dBm0dBm 6dB
+17dBm EDFA characteristics
Gain: 23dB (max = 17dBmNoise figure: < 6dBMax input: 6dBm
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60 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Span Design LimitsDispersion
Source and receiver characteristicsTx: 0dBmRx sensitivity: 28dBm Dispersion tolerance: 1600ps/nmOSNR requirements: 21dB
Span characteristicsDistance: 120kmSpan loss: .25dB/km (30dB total)Dispersion: 18ps/nm*km
Tx
Rx
Time Do
main 0ps/nm
Wavelen
gth
Domain
20km
360ps/nm
100km
1800ps/nm
120km
2160ps/nm
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61 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Span Design LimitsDispersion Compensation
Source and receiver characteristicsTx: 0dBmRx sensitivity: 28dBm Dispersion tolerance: 1600ps/nmOSNR requirements: 21dB
Span characteristicsDistance: 120kmSpan loss: .25dB/km (30dB total)Dispersion: 18ps/nm*km
EDFA characteristicsGain: 23dB (Max +17dBm)Noise figure: < 6dBMax input: 6dBm
DCF characteristicsDispersion: 600ps/nmLoss: 10dB
Tx
Rx
Time Do
main
+12dBm 360ps/nm
20km
8dBm 1800ps/nm
100km
Wavelen
gth
Domain
EDFA
6dBm0dBm 6dB
+17dBm0ps/nm
DCF
(10dB)
13dBm 2160ps/nm
120km
23dBm 1560ps/nm
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62 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Span Design Limits of Amplification (OSNR)
Source and receiver characteristicsTx: 0dBmRx sensitivity: 28dBm Dispersion tolerance: 1600ps/nmOSNR requirements: 21dB
Span characteristicsDistance: 60km x 4 SpansSpan loss: .25dB/km (15dB/span)Dispersion: 18ps/nm*km
EDFA characteristicsGain: 23dB (Max +17dBm)
Noise figure: < 6dB
Max input: 6dBm
Tx
Rx
Time Do
main
60km
Wavelen
gth
Domain
EDFA
0dBm 6dB
EDFA
EDFA
EDFA
EDFA
+17dBmOSNR 39dB
Noise
Noise
+17dBm OSNR 21dB
Noise
Noise
+17dBm OSNR 27dB
Noise
Noise
+17dBm OSNR 15dB
Noise
Noise
DCF
DCF
60km
60km
60km
Noise
Noise
+17dBm OSNR 33dB
DCF
DCF
Too Low
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63 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Real Network Design Challenges
Complicated multi-ring designs
Multiple wavelengths
Any to any demand
Nonlinearities
Advanced modulation
Simulation and Network Design Software Is Used
to Simplify Design
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Rack diagrams
Step-by-step interconnect
Smooth transition from design to implementation
Any-to-any demand
Comprehensive analysis = first-time success
GUI-based network design entry
Bill of materials
Network Design Tools?Concept to Creation Easier
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Summary
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Summary
AttenuationCompensated by amplifiers
Dispersioncompensated by DCUs
OSNRLimits of amplification
Multi-channel considerations
Non-linear effects
Use design software for advanced designs
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67 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Q and A
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70 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicOPT-110112512_04_2006_c2
Optical FundamentalsAgendaModern Lightwave ErasOptical SpectrumTerminologyTerminologyFiber ImpairmentsITU Wavelength GridBit Error Rate (BER)Eye DiagramEye DiagramEye DiagramEye Mask TestingOptical PowerOptical Power BudgetOptical Power BudgetExampleA Few Words on Optical SafetyLaser Classifications/Safety IconsProtective Eyewear AvailableSome Final Words on Optical Equipment SafetyAnalog Transmission EffectsFiber GeometryFiber DimensionsGeometrical OpticsPropagation in Fiber Different Types of FiberAttenuation in FiberOther Causes of Attenuation in FiberOptical Attenuation Attenuation Response at Different WavelengthsAttenuation: Compensated by Optical AmplifiersThe Photoelectric Effect in ErbiumTypes of Dispersion A Snapshot on Chromatic DispersionLimitations from Chromatic Dispersion Combating Chromatic DispersionTransmission Over SM FiberWithout CompensationHow Far can I Go Without Dispersion?Dispersion CompensationPolarization Mode DispersionPolarization Mode Dispersion (PMD)Combating Polarization Mode DispersionFrom Linear to Non-Linear PropagationEffects of Nonlinearity Self-Phased Modulation (SPM) and Cross Phase Modulation (XPM) Four-Wave Mixing (FWM)Four-Wave Mixing (FWM) FWM and DispersionThe Three Rs of Optical NetworkingTypes of Single-Mode FiberFiber Dispersion CharacteristicsDifferent Solutions for Different Fiber TypesSpan Design LimitsAttenuationSpan Design LimitsAmplificationSpan Design LimitsDispersionSpan Design LimitsDispersion CompensationSpan Design Limits of Amplification (OSNR)Real Network Design ChallengesNetwork Design Tools?Concept to Creation EasierSummaryRecommended ReadingComplete Your Online Session Evaluation