In these PPT Lan and Optical, fiber link budget will be discussed in details.
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Optical Fiber Link and LAN Design ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 1
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Table 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 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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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 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Transmission Types •Two types of transmissions: 1. Link (point to point) 2. Network a. point to multipoint b. Mesh c. Ring ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Elements of Link/ Network Design • Transmitter : Operating wavelength (X), Linewidth (AX), Rise time, Bit-rate, Line format, Power level • Fiber : SMF/MMF, Fiber type - SMF28, DSF, etc, Cable loss, Spool length • Rx : P P Rise time SEN' SAT' ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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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 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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The Main Question • In Digital System - Data Rate - Bit Error Rate • In Analog System - Bandwidth - Signal to Noise Ratios The Main Problems • Attenuation and Loss • Dispersion ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Factors for Evaluating Fiber Optic System Design System Factor T e of Fiber Operating Wavelength Transmitter Power Source T e Receiver Sensitivity and Overload Characteristics Detector T e Considerations Sin le-mode or Multimode 780, 850, 1310 and 1550 nm t ical T icall ex ressed in dBm LED or Laser Typically expressed in dBm PIN Diode, APD or IDP ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 8
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Factors for Evaluating Fiber Optic System Design S stem Factor Modulation Code Bit Error Rate (BER) (Digital Systems Only) Signal to Noise Ratio Number of Connectors Number of Splices Environmental Requirements (cont.) Considerations AM, FM, PCM or Digital 10-9 , 10- Typical Specified in decibels (dB) Loss increases with the number of connectors Loss increases with the Humidity, Temperature, Exposure to sunlight Mechanical Requirements Flammability, Indoor/Out Application ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 9
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Optical Transmitter/ Sources LEDs Output Power Modulation Bandwidth • Center Wavelength • Spectral Width Source Size • Pattern Laser Diodes • Output Power Modulation Bandwidth • Center Wavelength, Number of Modes Chirp, Linewidth • Mode Field of the Gaussian be ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 10
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Optical Fiber Multimode Fiber Attenuation Multimode Dispersion Chromatic Dispertion Numerical Aperture Core Diameter Single-Mode Fiber Attenuation Chromatic Dispersion • Cutoff Wavelength • Spot Size ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Optical Receiver/ Photodiode •Risetime/Bandwidth •Response Wavelength Range •Saturation Level •Minimum Detection Level ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 12
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Simple Link Medium and Devices ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 13
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Link Budget Considerations Three types of budgets: (1) Power Budget (2) Bandwidth or Rise Time Budget ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 14
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POWER BUDGET ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 15
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Power Budget Requirements: PB : > PMIN PRX = Received Power PMIN = Minimum Power at a certain BER = - Total Losses + Total Gain - P PTX = Transmitted Power MARGIN MARGIN ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 16
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• Loss,L = Gain,G — Requirements Cont'd: LIL + L + L + L fiber non-linear conn. LIL = Insertion Loss = Fiber Loss L fiber = Connector Loss L conn. = Non-linear Loss L non-linear — Gain amp + G non-linear Gainamp = Amplifier Gain = Non-linear Gain G non-linear ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 17
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dB, dBm, mW dB = 10 log (PI/P2) dBm Value % of mW 0.0 -13.0 -30.0 -40.0 100% 5% 0.01% Power 1.0mW 50.ogw I.ogw 100.onw Application Typical laser Peak Output Typical PIN Receiver Sensitivity Typical APD Receiver Sensitivity Typical LED Peak Output ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 18
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dB 1 2 3 4 5 6 7 8 9 10 Power Out as a % of Power In 40% Decibel to Power Conversion % of Power Lost ETM7172 OPTICAL COMMUNICATION SYSTEMS Remarks h the ower 1/4 the power 1/5 the power 1/6 the power 1/8 the power 1/10 the po Multimedia University 19
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dB 25 30 40 50 Power Out as a % of Power In 0.01% 0.001% Decibel to Power Conversion % of Power Lost 99.7% 99.9% 99.99% 99.999% ETM7172 OPTICAL COMMUNICATION SYSTEMS Remarks 1/300 the power 1/1000 the power 1/10,000 the power 1/100,000 the power Multimedia University 20
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Example: Power Budget Measurement for Long Haul Transmission 185 km Connector Splice = O dBm PTx LOGOöb? Number Splice Lo Connector Loss = 0.2 dB p Margin ETM7172 OPTICAL COMMUNICATION SYSTEMS 1 = -28 dBm Multimedia University 21
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Simple Calculation.... Fiber Loss = 0.25 dB/km X 185 km = 46.3 dB Splice Loss = 0.1 dB X 46 CONCL-LSION: = 0.4 dB BADSYSTEM!! p Margin = - Total Losses - P Margin = 0-51.3-6 -57.3 dB Power Budget, < PE !! ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 22
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How To Solve? Answer... Place an amplifier And... What is the gain value? Where is the location? ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 23
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First we calculate the amplifier's gain.. • -(-57.3) Gain P SEN - > 28 RX To make it easy, Now... Gain 29.3 dB Gain 30 dB Where to put the amplifier? ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 24
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Three choices available for the location Power Amplifier — At the transmitter Preamplifier — At the receiver In Line — Any point along fiber ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 25
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Let us check one by one... Power Amplifier: + Gain = POUT = 30 dBm O + 30 But is there any power amplifier with 30 dBm POUT? NO, THERE ISN'T Hence . ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 26
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What about Preamplifier? Remember... received = -57 dBm POUT Preamplifier with 30 dB available? Yes But, can it take —57 dBm? Typically, NO Hence . ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 27
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But, so... Let us check In Line Amplifiers 30 dB gain amplifier available here... What value can it take? Typically -30 dBm O Now, we can find the location... ETM7172 OPTICAL COMMUNICATION SYSTEMS O Multimedia University 28
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PTX Where is the —30 dBm point? - Loss At That Point = O dBm - 30 dB Loss At That Pont • = -30 dBm Assume Other Loss = 0, Loss At That Point = Fiber Loss, 30 = u x Length of That Point Remember u = 0.25, Point Length = 30/0.25 = 120 km But 120 km from TX, No. of splice = 120/4 = 30 Splice Loss = 0.1 dB x 30 = 3 dB ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 29
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Also remember connector loss at amplifier and TX... + I connector at TX .....................................+ 2 connectors Connector Loss = 0.2 dB x 3 - - 0.6 dB Actually, at 120 km, Total Losses = Fiber Loss + Splice Loss + Connector Loss = 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 k Good Location - - 120 km - 14.4 km = 105. ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 30
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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!! = O dBm PTx 185 km Splice 105.6 KM ETM7172 OPTICAL COMMUNICATION SYSTEMS Connector PSEN Multimedia University 31
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Server A = -15 dBm Example: Power Budget Measurement for LAN = -25 dBm Number Splice Lo Connector Loss = 0.5 dB 500 m Using 850nm LOGOOD? p Margin = 2 dB ETM7172 OPTICAL COMMUNICATION SYSTEMS Server B [D Multimedia University 32
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BANDWIDTH BUDGET ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 33
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System Rise Time • Calculate the total rise times TX, Fiber, Rx • Calculate Fiber rise time, T Fiber = D x AX x L fiber D = Dispersion Coefficient AX = Linewidth L = Fiber Length - normally given by manufacturer Tx Rise Time, Rx Rise Time, - normally given by ma a ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 34
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Total Rise time T sys • Tsys= 1 . 1 .+Tf. ETM7172 OPTICAL COMMUNICATION SYSTEMS 2h1/2 Multimedia University 35
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Bandwidth Budget Medium and Devices ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 36
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What is a good Rise time? • For a good reception of signal 0.7 x Pulse Width (PW) 1/BitRate for NRZ 1/2BitRate for RZ ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 37
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Example: Rise Time Budget Measurement for Long Haul Application Tx rise time, = 0.1 ns Rx rise time, TRE 0.5 ns Linewidth(AX) = 0.15 nm Dispersion Coefficient, D = 18 ps/nm-km Fiber length - - 150km Bit Rate = 622Mbps Format = RZ ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 38
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Simple Calculation.... Fiber rise time, TE =Length x D x Linewidth(AX) = 150 km x 18 x 0.15 nm = 0.4 ns = 1.1M TLS2 + T p D 2 + T F 2 Total Rise time T SYS = 1.1M 0.01 + 0.25 + 0.16 = 0.77 ns ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 39
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Let say, Bit Rate = STM 4 = 622 Mbps Format = RZ 0.7 x Pulse Width (PW) Pulse Width (PW) = = 1.6 ns 0.77 ns < 0.7 x 1.6 ns 0.77 < 1.1 ns Good Rise Time Budget!! ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 40
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Let say, Bit Rate = STM 16 = 2.5 Gbps Format = RZ 0.7 x Pulse Width (PW) Pulse Width (PW) = = 0.4 ns 0.77 ns < 0.7 x 0.4 ns 0.77 0.28 ns Bad Rise Time Budget!! ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Budget Summary Source (LED vs. LD) Modulation Bandwidth Output Power Radiation pattern Option 850nm 1310nm 1550nm LED LED LED (far- field pattern) LD (Gaussian beam) Power Mediocre Good Very good Mediocre Good Bandwidth Budget Bad Good Very good Bad Good Bad Good ETM7172 OPTICAL COMMUNICATION SYSTEMS Financial Cheap Less expensive Expensive Cheap Expensive Cheap Expensive Cheap six.' Multimedia University 42
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Budget Summary B Fiber Attenuation Dispersion Numerical Aperture Core Diameter Option MM SM MM SM MM SM MM SM Power Budget Mediocre Good Mediocre Good Mediocre Good Mediocre Good Bandwidth Budget Mediocre Good Mediocre Good Mediocre Good Mediocre Good ETM7172 OPTICAL COMMUNICATION SYSTEMS Financial Cheap Expensive Cheap Expensive Cheap Expensive Cheap Ex Multimedia University 43
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Budget Summary c Receiver (PIN vs. Rise time/ B andwidth Response wavelen th ran e Saturation Level Minimum detection level Option PIN APD PIN APD PIN APD PIN APD Power Budget Mediocre Good Mediocre Good Mediocre Good Mediocre Good Bandwidth Budget Mediocre Good Mediocre Good Mediocre Good Mediocre Good Financial Cheap Expensive Cheap Expensive Cheap Expensive Cheap Ex ETM7172 OPTICAL COMMUNICATION SYSTEMS ve Multimedia University 44
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Sensitivity Analysis •Minimum optical power that must be present at the receiver in order to achieve the performance level required for a given system, ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 45
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Factors 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 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 46
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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 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 47
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5. Bit error rate main quality criterion for a digital transmission system BER = Q [MIMIC/ (4 . NO . B) ] where = Noise power spectral density (A2/Hz) No IMIN = Minimum effective signal amplitude (Amps) = Bandwidth B Q(x) = Cumulative distribution function (Gaussian distribution) ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 48
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Eye Diagrams Onrv ETM7172 OPTICAL COMMUNICATION SYSTEMS Ill Multimedia University 49
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Signal to Noise Ratio SNR = S/N S - represents the information to be transmitted N - integration of all noise factors over the full system bandwidth SNR (dB) = 10 log10 (SIN) ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 50
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Cost/Performance Considerations Components considerations such as : • Light Emitter Type Emitter Wavelength • Connector Type • Fiber Type • Detector Type ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University
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Summary • 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 e the demands of a given application. ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 52
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Summary • 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 ti period, fall time, width and amplitude. ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 53
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TUTORIAL Make the rise-time budget for a 0.85-gm, 10-km fiber link designed to operate at 50 Mb/s. The LED transmitter and the Si p—i—n receiver have rise times of 10 and 15 ns, respectively. The graded-index fiber has a core index of 1.46, A = 0.01 and D = 80 ps/(km-nm). The LED spectml width is 50 nm. Can the system be designed to operate with the NRZ format? Make the power budget and calculate the maximum transmission distance for a I .3-gm lightwave system operating at I (X) Mb/s and using an LED for launching 0.1 mW of average power into the libell Assume I-dB/km fiber loss, 0.2-dB splice loss every 2 km, I-dB connector loss at each end of fiber link, and 100- nW receiver sensitivity. Allow 6-dB system margin. ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 54
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Make the power 'budget and calculate the maximum transmission distance for a 1.3-gm lightwave system operating at 1(1) Mb/s and using an LED for launching 0.1 mW of average power into the fiber. Assume I-dB/km fiber loss, 0.2-dB splice loss every 2 km, I-dB connector loss at each end of fiber link, and 100- nW receiver sensitivity Allow 6-dB system margin. ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 55
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Thank You ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University 57
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