1 etm7172 optical communication systems multimedia university l5 optical fiber link and lan design
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1ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
L5
Optical Fiber Link and LAN Design
L5
Optical Fiber Link and LAN Design
2ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
Table of contentTable of content
Transmission Type
Elements in Network Design
Factors for Evaluating Fiber Optic System Design
Link Budget Considerations
Power Budget
Power Budget Requirement
Example : Long-haul Transmission System
Example : LAN
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Table of content (cont.)Table of content (cont.)
Bandwidth Budget
System Rise Time
Example on STM-4, STM-16 and STM-64
Budget Summary
Sensitivity Analysis
Eye Diagrams
Signal to Noise Ratio (SNR)
Cost/ Performance Considerations
Summary
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Transmission TypesTransmission Types
Two types of transmissions:1. Link (point to point)
2. Networka. point to multipointb. Meshc. Ring
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Elements of Link/ Network DesignElements of Link/ Network DesignTransmitter :
Operating wavelength (), Linewidth (),Rise time, Bit-rate, Line format, Power level
Fiber : SMF/MMF, Fiber type – SMF28, DSF, etc, Cable loss, Spool length
Rx : PSEN, PSAT, Rise time
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Elements of Link/ Network Design (cont.) Elements of Link/ Network Design (cont.)
Connection:
No. of splice, Splice loss
No. of connectors, Connector Loss
In Line Devices:
Splitter, Filter, Attenuator, Amplifier Insertion loss, Gain
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The Main Problems
Attenuation and Loss
Dispersion
The Main Question
In Digital System
- Data Rate
- Bit Error Rate
In Analog System
- Bandwidth
- Signal to Noise
Ratios
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System Factor Considerations Type of Fiber Single-mode or Multimode Operating Wavelength 780, 850, 1310 and 1550 nm
typical Transmitter Power Typically expressed in dBm Source Type LED or Laser Receiver Sensitivity and Overload Characteristics
Typically expressed in dBm
Detector Type PIN Diode, APD or IDP
Factors for Evaluating Fiber Optic System Design
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System Factor Considerations Modulation Code AM, FM, PCM or Digital Bit Error Rate (BER) (Digital Systems Only)
10-9 ,10-12 Typical
Signal to Noise Ratio Specified in decibels (dB) Number of Connectors Loss increases with the number of
connectors Number of Splices Loss is Loss increases with the
number of splices Environmental Requirements
Humidity, Temperature, Exposure to sunlight
Mechanical Requirements Flammability, Indoor/Outdoor Application
Factors for Evaluating Fiber Optic System Design (cont.)
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Optical Transmitter/ Sources Optical Transmitter/ Sources
LEDs
Output Power
Modulation Bandwidth
Center Wavelength
Spectral Width
Source Size
Far-Field Pattern
Laser Diodes• Output Power• Modulation
Bandwidth• Center Wavelength,
Number of Modes• Chirp, Linewidth• Mode Field of the
Gaussian beam
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Optical FiberOptical Fiber
Multimode Fiber
Attenuation
Multimode Dispersion
Chromatic Dispertion
Numerical Aperture
Core Diameter
Single-Mode Fiber• Attenuation• Chromatic
Dispersion• Cutoff Wavelength• Spot Size
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Optical Receiver/ PhotodiodeOptical Receiver/ Photodiode
• Risetime/Bandwidth
• Response Wavelength Range
• Saturation Level
• Minimum Detection Level
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Simple Link Simple Link
TX RX
Medium and Devices
OA
OA
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Link Budget ConsiderationsLink Budget Considerations
Three types of budgets:
(1) Power Budget
(2) Bandwidth or Rise Time Budget
(3) ?
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POWER BUDGETPOWER BUDGET
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Power Budget Requirements: PB : PRX > PMIN
PRX = Received PowerPMIN = Minimum Power at a certain BER
PRX = PTX – Total Losses + Total Gain - PMARGIN
PTX = Transmitted Power
PMARGIN ≈ 6 dB
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Requirements Cont’d:Requirements Cont’d:
Loss,L = LIL + Lfiber + Lconn. + Lnon-linear
LIL = Insertion Loss
Lfiber = Fiber Loss
Lconn.= Connector Loss
Lnon-linear= Non-linear Loss
Gain,G = Gainamp + Gnon-linear
Gainamp = Amplifier Gain
Gnon-linear = Non-linear Gain
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dB, dBm, mWdB, dBm, mW
dB = 10 log (P1/P2)dBm Value % of 1 mW Power Application
0.0 100% 1.0 mW Typical laser Peak Output
-13.0 5% 50.0W Typical PIN Receiver Sensitivity
-30.0 0.1% 1.0W Typical APD Receiver Sensitivity
-40.0 0.01% 100.0W Typical LED Peak Output
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dB Power Out as a % of Power In
% of Power Lost
Remarks
1 79% 21% - 2 63% 37% - 3 50% 50% ½ the power 4 40% 60% - 5 32% 68% 6 25% 75% ¼ the power
7 20% 80% 1/5 the power
8 16% 84% 1/6 the power
9 12% 88% 1/8 the power
10 10% 90% 1/10 the power
Decibel to Power Conversion
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dB Power Out as a % of Power In
% of Power Lost
Remarks
25 0.3% 99.7% 1/300 the power
30 0.1% 99.9% 1/1000 the power
40 0.01% 99.99% 1/10,000 the power
50 0.001% 99.999% 1/100,000 the power
Decibel to Power Conversion
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IS THIS SYSTEM GOOD?
Example: Power Budget Measurement for Long
Haul Transmission
PTx = 0 dBm
185 km
PSEN = -28 dBm
Splice
Attenuation Coefficient, = 0.25 dB/km
Dispersion Coefficient, D = 18 ps/nm-km
Number of Splice = 46
Splice Loss = 0.1 dB
PMargin = 6 dB
Connector Loss = 0.2 dB
Connector
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CONCLUSION: BAD
SYSTEM!!
Simple Calculation….
Fiber Loss = 0.25 dB/km X 185 km = 46.3 dB
Splice Loss = 0.1 dB X 46 = 4.6 dB
PMargin = 6 dB
Total Losses = 46.3 + 4.6 + 0.4 = 51.3 dB
Power Budget, PRX < PSEN !!
PRX = -57.3 dB
PRX = PTX – Total Losses – PMargin
= 0 – 51.3 – 6
Connector Loss = 0.2 dB X 2 = 0.4 dB
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How To Solve?Answer…Place an
amplifierBut… What is the gain value??
Where is the location?And…
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First we calculate the amplifier’s gain..
Gain PSEN - PRX
Gain -28 – (-57.3)Gain 29.3 dB
To make it easy,Gain 30 dB
Now…Where to put the amplifier?
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Three choices availablefor the location
Power Amplifier – At the transmitter
Preamplifier – At the receiver
In Line – Any point along fiber
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Let us check one by one…
Power Amplifier: PTX + Gain = POUT 0 + 30 = 30
dBmBut is there any power amplifier with 30 dBm POUT? NO, THERE ISN’T
Hence …
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What about Preamplifier?
POUT received = -57 dBm
Remember…
Preamplifier with 30 dB available?Yes
But, can it take –57 dBm?
Typically, NO
Hence …
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Let us check In Line Amplifiers
30 dB gain amplifier available here…
But, What value can it take?
Typically –30 dBm
So…
Now, we can find the location…
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Where is the –30 dBm point?
PTX – Loss At That Point = 0 dBm – 30 dB
Loss At That Point = -30 dBm
30 = x Length of That PointRemember = 0.25,Point Length = 30/0.25
= 120 kmBut 120 km from Tx,
No. of splice = 120/4
= 30
Assume Other Loss = 0, Loss At That Point = Fiber Loss,
Splice Loss = 0.1 dB x 30 = 3 dB
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Also remember connector loss at amplifier and Tx…
2 connectors
Connector Loss = 0.2 dB x 3 = 0.6 dB
Total Losses = Fiber Loss + Splice Loss + Connector Loss
Actually, at 120 km,
= 30 + 3 + 0.6 = 33.6 dB
33.6 dB > 30 dB!! NOT GOOD!
Now, We have excess of 3.6 dB…Find the distance,
Fiber Loss Length = 3.6/0.25 = 14.4 km
Good Location = 120 km – 14.4 km = 105.6 km
+ 1 connector at Tx
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Let us confirm the answer…At 105.6 km from Tx,
Fiber Loss = 0.25 x 105.6 = 26.4 dB
No. of Splice at 105.6 km = 105.6/4 =26.4 = 27
Splice Loss = 0.1 x 27 = 2.7 dB
Total Losses = 26.4 + 2.7 = 29.1 dB
29.1 dB < 30 dB !!CONFIRM…105.6 KM IS A GOOD LOCATION!!
PTx = 0 dBm
185 km
PSEN = -28 dBmSplice Connector
105.6 KM
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IS THIS SYSTEM GOOD?
PTx = -15 dBm
500 m
Using
850nm PSEN = -25 dBmAttenuation Coefficient, = 4.5 dB/km
Dispersion Coefficient, D = 18 ps/nm-km
Number of Splice = 0
Splice Loss = 0 dB
PMargin = 2 dB
Connector Loss = 0.5 dB
Server A Server B
Example: Power Budget Measurement for LAN
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BANDWIDTH BUDGET
BANDWIDTH BUDGET
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Calculate the total rise times Tx, Fiber, Rx
Calculate Fiber rise time, TFiber
Tfiber = D x x L
D = Dispersion Coefficient = LinewidthL = Fiber Length
Tx Rise Time, TTX = normally given by manufacturerRx Rise Time, TRX = normally given by manufacturer
System Rise TimeSystem Rise Time
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Total Rise time, Tsys:
Tsys=1.1(TTX2+TRX
2+Tfiber2)1/2
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Bandwidth BudgetBandwidth Budget
TX RX
Medium and Devices
T’
Δτ = T’ - T
T
OA
OA
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What is a good Rise time?
For a good reception of signalTsys < 0.7 x Pulse Width (PW)
PW = 1/BitRate for NRZ1/2BitRate for RZ
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Example: Rise Time Budget Measurement
for Long Haul Application
Tx rise time, TTX = 0.1 nsRx rise time, TRX= 0.5 nsLinewidth() = 0.15 nm
Dispersion Coefficient, D = 18 ps/nm-kmFiber length = 150km
Bit Rate = 622MbpsFormat = RZ
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Fiber rise time, TF =Length x D x Linewidth() = 150 km x 18 x 0.15 nm
= 0.4 ns
Total Rise time, TSYS = 1.1 TLS2 + TPD
2 + TF
2 = 1.1 0.01 + 0.25 + 0.16
Simple Calculation….
TSYS = 0.77 ns
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Let say,Bit Rate = STM 4 = 622 MbpsFormat = RZ
Tsys < 0.7 x Pulse Width (PW)
Pulse Width (PW) = 1/(622x106)
= 1.6 ns
0.77 ns < 0.7 x 1.6 ns
0.77 ns < 1.1 ns !!
Good Rise Time Budget!!
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Let say,Bit Rate = STM 16 = 2.5 GbpsFormat = RZ
Tsys < 0.7 x Pulse Width (PW)
Pulse Width (PW) = 1/(2.5x109)
= 0.4 ns
0.77 ns < 0.7 x 0.4 ns
0.77 ns ≥ 0.28 ns !!
Bad Rise Time Budget!!
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Budget SummaryBudget Summary Option Power
BudgetBandwidth
BudgetFinancial
A Source (LED vs. LD)
Δλ
850nm Mediocre Bad Cheap
1310nm Good Good Less expensive
1550nm Very good Very good Expensive
Modulation Bandwidth
LED NA Bad Cheap
LD NA Good Expensive
Output Power LED Mediocre NA Cheap
LD Good NA Expensive
Radiation pattern LED (far-field pattern)
NA Bad Cheap
LD (Gaussian beam)
NA Good Expensive
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Budget SummaryBudget Summary
B Fiber Option Power Budget
Bandwidth Budget
Financial
Attenuation MM Mediocre Mediocre Cheap
SM Good Good Expensive
Dispersion MM Mediocre Mediocre Cheap
SM Good Good Expensive
Numerical Aperture (NA)
MM Mediocre Mediocre Cheap
SM Good Good Expensive
Core Diameter MM Mediocre Mediocre Cheap
SM Good Good Expensive
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Budget SummaryBudget SummaryC Receiver (PIN vs.
APD)
Option Power Budget
Bandwidth Budget
Financial
Rise time/ Bandwidth
PIN Mediocre Mediocre Cheap
APD Good Good Expensive
Response wavelength range
PIN Mediocre Mediocre Cheap
APD Good Good Expensive
Saturation Level PIN Mediocre Mediocre Cheap
APD Good Good Expensive
Minimum detection level
PIN Mediocre Mediocre Cheap
APD Good Good Expensive
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Sensitivity AnalysisSensitivity Analysis
Minimum optical power that must be present at the receiver in order to achieve the performance level required for a given system.
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Factors will affect this analysisFactors will affect this analysis
1. Source Intensity Noise - Refers to noise generated by the LED or Laser
Phase Noise - the difference in the phases of two optical wavetrains separated by time, cut out of the optical wave
Amplitude Noise - caused by the laser emission process.
2. Fiber Noise
Relates to modal partition noise
3. Receiver Noise
Photodiode, conversion resistor
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4. Time Jitter and Intersymbol Interference
Time Jitter - short term variation or instability in the duration of a specified interval
Intersymbol Interference
result of other bits interfering with the bit of interest
inversely proportional to the bandwidth
Eye diagrams - to see the effects of time jitter and intersymbol interference
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5. Bit error rate - main quality criterion for a digital transmission system
BER = Q [IMIN2/ (4 . N0 . B) ]
where :
N0 = Noise power spectral density (A2/Hz)
IMIN = Minimum effective signal amplitude (Amps)
B = Bandwidth
Q(x) = Cumulative distribution function (Gaussian distribution)
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Eye Diagrams
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Signal to Noise RatioSignal to Noise Ratio
SNR = S/NS - represents the information to be transmitted
N - integration of all noise factors over the full system bandwidth
SNR (dB) = 10 log10 (S/N)
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Cost/Performance ConsiderationsCost/Performance Considerations
Components considerations such as : Light Emitter Type
Emitter Wavelength
Connector Type
Fiber Type
Detector Type
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SummarySummary
The key factors that determine how far one can transmit over fiber are transmitter optical output power, operating wavelength, fiber attenuation, fiber bandwidth and receiver optical sensitivity.
The decibel (dB) is a convenient means of comparing two power levels.
The optical link loss budget analyzes a link to ensure that sufficient power is available to meet the demands of a given application.
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SummarySummary
Rise and fall times determine the overall response time and the resulting bandwidth.A sensitivity analysis determines the amount of optical power that must be received for a system to perform properly.Bit errors may be caused by source intensity noise, fiber noise, receiver noise, time jitter and intersymbol interference.The five characteristics of a pulse are rise time, period, fall time, width and amplitude.
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TUTORIALTUTORIAL
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Thank YouThank You