PPT On Optical Fiber Communication System

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This PPT will give a brief introduction of the optical fiber communication system.

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    Optical Fibre Communication Systems Lecture 8 - Systems Professor Z Ghassemlooy Electronics & It Division School of Engineering Sheffield Hallam University U.K. www.shu.ac.uk/ocr Prof. Z Ghassemlooy 1
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    Contents • System Design Digital Systems • Link Power Budget • Link Rise Time (Bandwidth) Budget • Transmission Distance • Analogue Systems Prof. Z Ghassemlooy 2
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    Fiber Optic System Design There are many factors that must be considered to ensure that enough light reaches the receiver. Without the right amount of light, the entire system will not operate properly. Input EFectrCal Slgri*l Optical Transmitter Output Electrul %nai Transmitter Supply 10 Splice Launch Power OpUcal Spßce Loss F/O Cable from Splice Loss Recelved Power Optical Receiver Power Supply Prof. Z Ghassemlooy 3
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    Fiber Optic System Design- Step-by- Step 0 Select the most appropriate optical transmitter and receiver combination based upon the signal to be transmitted (Analog, Digital, Audio, Video, RS-232, RS-422, RS-485, etc.). Determine the operating power available (AC, DC, etc.). Determine the special modifications (if any) necessary (Impedances, bandwidths, connectors, fiber size, etc.). Carry out system link power budget. Carry out system rise time budget (I.e. bandwidth budget). ' If it is discovered that the fiber bandwidth is inadequate for transmitting the required signal over the necessary distance, then either select a different transmitter/receiver (wavelength) combination, or consider the use of a lower loss premium fiber Prof. Z Ghassemlooy 4
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    Digital Systems 0 Compared with analogue systems: — It Gives superior performance — It reduces problems associated with the optical source non- linearities and temperature dependency (in baseband transmission) e Provide ideal channel for data transmission e Information is carried in the baseband using Intensity Modulation (1M). Prof. Z Ghassemlooy 5
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    Link Power Budget Transmitter Connector Optical source Fiber flylead Splices sp sp Receiver Optical fibers Connector sp Fiber flylead Photon detector O Connector (optional) Total loss LT - — a L + lc + Isp P = Receiver sensitivity (i.e. minimum power requirement) SM = System margin (to ensure that small variation the system operating parameters do not result in an unacceptable decrease in system performance) Prof. Z Ghassemlooy 6
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    Link Power Budget - Example 1 Parameters • Transmitter • Average transmitted power • Fibre coupling losses • Channel • Fibre loss • Splitting losses • Splice & Connector losses • Fibre dispersion & nonlinearity • Receiver • Signal power at the receiver Receiver sensitivity Value All lossess System Margin (-20 dBm -(-30 dBm)) Prof. Z Ghassemlooy dB 4.8 dBm -3.7 dB -15.7 dB -10 dB -0.79 dB -26.79 dBm -31 dBm +4.1 dB 7
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    Link Power Budget - Example 2 Transmitter — Date rate = 500 Mb/s — Source Laser @ 1300 nm — Coupling power = 2 mW (3 dBm) into a 10 um fibre. Channel — Mono mode fibre of length 60 km and a loss of 0.3 dB/km Connector loss = 1 dB/connector Splicing every 5 km with a loss = 0.5 dB /splice Receiver: PIN @ 1300 nm BER = 10-9 System margin — Prof. Z Ghassemlooy 8
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    Link Power Budget - Example 2 contd. Receiver sensitivity -29 dBm Pt-Po=LT+SM LT = dB) + 0.3(60) + 0.5 (11) = 25.5 dB thus 3 +29 = 25.5 dB+SM therefore 5.5 dB o -20 40 50 —60 -70 80 .5 InGaAs pin ( 1300 nm) lnGaA APD (1550 n 1 2 Si pin (800-900 nm) Si APD (800-900 nm) 5 10 20 Data rate (Mb/s) 100 200 Prof. Z Ghassemlooy 500 1000 G Keiser 9
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    Link-Power Launch po er Budget - Example 3 10 Flylead-coupled power from LED Connector loss Cable-coupled power into fibr Link power budget can be shown graphically in terms of receiver sensitivity Vs. the data rate 0 o 20 30 40 50 Loss allocated to cable and splice loss 6-dB system margin 3.5-dB/km cable (and splice) loss Achievable transmission distance Connector loss Launch power into fibre G Keiser pin receiver sensitivity LED/PIN, @ 20 Mbps 2 Prof. Z Ghassemlooy 3 Distance (km) 4 5 6 10
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    Link-Power Budget - contd. 0 Dispersion -equalisation penalty is given as: (dB) Where BT is the bit rate, is the rms pulse width. Therefore, the total channel loss is given as: Total loss = + lc + + DL (dB) DL is only significant in wideband multi-mode fibre systems Prof. Z Ghassemlooy 11
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    Rise Time Budget 0 The system design must also take into account the temporal response of the system components. e The total loss LT (given in the power budget section) is determined in the absence of the any pulse broadening due to dispersion. e Finite bandwidth of the system (transmitter, channel, receiver) may results in pulse spreading (i.e. intersymbol interference), giving a reduction in the receiver sencitivity. I.e. worsening of BER or SNR 0 The additional loss penalty is known as dispersion- equalisation or ISI penalty. Prof. Z Ghassemlooy 12
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    Rise Time Budget - The total system rise time contd. sys 0.5 2 i—l 0.5 sys t s + t inter -I-t intra -I-t d Fibre Fibre Source intramodal Detector intermodal Note - 3 dB bandwidth of a simple low pass RC filter is given as: 1 27tRC With a step input voltage into the RC filter, the rise time of the output voltage is: 0.35 tr = 2.2B = Prof. Z Ghassemlooy 13
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    Rise Time Budget - contd. For a fibre optic link: 1 For RZ data format For NRZ data format 21 O t sys 1 0.35 Bit rateR=B 0.35 t sys Bit rate R = B 0.75 BNRZ t sys —1/2x Prof. Z Ghassemlooy 14
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    Transmission Distance -1 st window Multi-mode, Input power Pt = -13 dB LED (0 dBm laser), fibre loss = 3.5 dB/km, SM = 6 dB BER = 109 20 16 12 8 4 1 Attenuation limit with laser/ D Attenuation limit with LED pin Material dispersion limit (LED) (0.07ns/(nm-km) @ 1=800 nm) 20 ata rate (Mb s Laser/APD limit 50 100 Modal dispersion limit for fibre with bandwidth of '800 MHz/km 200 2 P 5 10 500 o: -51dBm Si PIN G Keiser PO: -38dBm -64 dBm Si APD -57dBm Prof. Z Ghassemlooy 15
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    Transmission Distance -3rd window D = 2.5 ps/(nm.km), fibre loss = 0.3 dB/[email protected] 1550nm, Pt = 0 dBm laser, PO = 11.5 log B -71dBm forAPD, and = 11.5 log B- 60.5 dBm for pin o o 200 150 100 50 O 50 RZ dispersion NZR dispersion limit: 01 = 3.5 nm Attenuation limit with lnGaAs APD Attenuation limit with InGaAs pin 100 200 1000 NZR dispersion limit: 01 = I nm 2000 500 Data éate (Mb/ s) Prof. Z Ghassemlooy 5000 G Keiser 16
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    Analogue System 0 The system must have sufficient bandwidth to pass the HIGEST FREQUENCIES. e Link Power budget is the same as in digital systems e Rise Time budget is also the same, except for the system bandwidth which is defined as: 0.35 sys sys Prof. Z Ghassemlooy 17

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