Ch9Sec1

Ch9Sec1 - THE FIBER FORUM Fiber Optic Communications...

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Dr. Joseph C. Palais 9.1 1 THE FIBER FORUM Fiber Optic Communications Dr. JOSEPH C. PALAIS PRESENTED BY
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Dr. Joseph C. Palais 9.1 2 Chapter 9 Distribution Networks and Fiber Components
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Dr. Joseph C. Palais 9.1 3 Fiber Networks: Point-to-Point One-way transmission. One transmitter and one receiver. Ex. Telephone network Distributed Many transmitters and receivers and shared transmission line (fiber). Ex. Local-area networks (LAN) Cable TV
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Dr. Joseph C. Palais 9.1 4 Section 9.1 Distribution Networks
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Dr. Joseph C. Palais 9.1 5 The four-port directional coupler (DC) is important in distribution networks. Input P 1 P 2 P 3 P 4 1 2 3 4 For our definitions (to follow), we assume and the input power is at port 1. DC 2 1 P P
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Dr. Joseph C. Palais 9.1 6 1. Throughput Loss L THP = - 10 log (P 2 /P 1 ) (9-1) The reduction in power from port 1 to port 2. 2. Tap Loss L TAP = - 10 log (P 3 /P 1 ) (9-2) The reduction in power from port 1 to port 3.
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Dr. Joseph C. Palais 9.1 7 3. Directionality L D = - 10 log (P 4 /P 1 ) (9-3) In the ideal case P 4 = 0, so that L D = infinite Typically, L D > 40 dB 4. Excess Loss L E = - 10 log [(P 2 + P 3 ) /P 1 ] (9-4) In the ideal case, P 2 + P 3 = P 1, so that L E = 0 dB Typically, L E is a few tenths dB
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Dr. Joseph C. Palais 9.1 8 In practice, due to undesirable losses (e.g.,scattering, imperfect construction) (P 2 + P 3 ) < P 1 L E represents these losses 5. Splitting Ratio SR= (P 2 /P 3 ) Couplers are often described (named) by their splitting ratio or their tap loss.
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Dr. Joseph C. Palais 9.1 9 Given the tap loss for an ideal coupler (L E = 0, L D = infinite ), produce a table showing the splitting ratio and the throughput loss. The result is L TAP (dB) (P 3 /P 1 ) SR (P 2 /P 3 ) L THP (dB) 3 1/2 1:1 1 3 6 1/4 3:1 3 1.25 10 1/10 9:1 9 0.46 Calculation of L THP from L TAP starts on the next slide.
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Dr. Joseph C. Palais 9.1 10 Now, L TAP = - 10 log (P 3 / P 1 ) Thus (9-5) TAP 3 - 10 1 L P =10 P - = - - TAP THP L 10 L 10 log 1 10 Compute L THP in terms of L TAP for an ideal coupler. L THP = - 10 log (P 2 /P 1 ) = - 10 log [(P 1 - P 3 ) /P 1 ] = - 10 log [1- (P 3 /P 1 )]
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Dr. Joseph C. Palais 9.1 11 Now account for excess losses in the calculation of L TAP and L THP .
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Dr. Joseph C. Palais 9.1 12 L E = - 10 log [(P 2 + P 3 ) /P 1 ] = - 10 log [(P 2 / P 1 )[1 + (P
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Ch9Sec1 - THE FIBER FORUM Fiber Optic Communications...

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