chapter 9

chapter 9 - THE FIBER FORUM Fiber Optic PRESENTED BY Click...

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Click to edit Master subtitle style 5/13/10 Dr. Joseph C. 9.1 11 THE FIBER FORUM Fiber Optic Dr. JOSEPH C. PALAIS PRESENTED BY
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5/13/10 Dr. Joseph C. 9.1 22 Chapter 9 Distribution Networks and Fiber Components
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5/13/10 Dr. Joseph C. 9.1 33 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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5/13/10 Dr. Joseph C. 9.1 44 Section 9.1 Distribution Networks
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5/13/10 Dr. Joseph C. 9.1 55 The four-port directional coupler (DC) is important in distribution networks. Input P1 P2 P3 P4 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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5/13/10 Dr. Joseph C. 9.1 66 1. Throughput Loss LTHP = - 10 log (P2 /P1 ) (9-1) The reduction in power from port 1 to port 2. 2. Tap Loss LTAP = - 10 log (P3 /P1 ) (9-2) The reduction in power from port 1 to port 3.
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5/13/10 Dr. Joseph C. 9.1 77 3. Directionality LD = - 10 log (P4 /P1 ) (9-3) In the ideal case P4 = 0, so that LD = infinite Typically, LD > 40 dB 4. Excess Loss LE = - 10 log [(P2 + P3) /P1 ] (9-4) In the ideal case, P2 + P3 = P1, so that LE = 0 dB Typically, LE is a few tenths dB
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5/13/10 Dr. Joseph C. 9.1 88 In practice, due to undesirable losses (e.g.,scattering, imperfect construction) (P2 + P3 ) < P1 LE represents these losses 5. Splitting Ratio SR= (P2 /P3 ) Couplers are often described (named) by their splitting ratio or their tap loss.
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5/13/10 Dr. Joseph C. 9.1 99 Given the tap loss for an ideal coupler (LE = 0, LD = infinite ), produce a table showing the splitting ratio and the throughput loss. The result is LTAP(dB) (P3 /P1 ) SR (P2 /P3 ) LTHP (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 LTHP from LTAP starts on the next slide.
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5/13/10 Dr. Joseph C. 9.1 1010 Now, LTAP = - 10 log (P3 / P1 ) Thus (9-5) TAP 3 - 10 1 L P =10 P - = - - TAP THP L 10 L 10 log 1 10 Compute LTHP in terms of LTAP for an ideal coupler. LTHP = - 10 log (P2 /P1 ) = - 10 log [(P1 - P3) /P1 ] = - 10 log [1- (P3 /P1 )]
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5/13/10 Dr. Joseph C. 9.1 1111 Now account for excess losses in the calculation of LTAP and LTHP .
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5/13/10 Dr. Joseph C. 9.1 1212 LE = - 10 log [(P2 + P3) /P1 ] = - 10 log [(P2 / P1 )[1 + (P3 / P2 )] LE = - 10 log (P2 / P1 ) - 10 log [(P2 + P3 ) /P2] LE = LTHP + 10 log [P2 / (P2 + P3 )] LTHP = LE - 10 log [P2 / (P2 + P3 )] LTHP = LE - 10 log {(P2 / P3 ) / [(P2 / P3 ) + 1]} In the ideal case, P2 + P3 =P1 so the last term is the ideal value of the throughput loss (i,e for a given actual splitting ratio). Define this term as L’THP
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5/13/10 Dr. Joseph C. 9.1 1313 The result is: LTHP = LE + L’THP (9-6a) L’THP = throughput loss when there is no excess loss, but the splitting ration is unchanged. Now find LTAP when excess losses are included. Begin with LE = - 10 log [(P2 + P3 ) /P1] = - 10 log [(P3/P1)( 1 + P2/P3)] = - 10 log (P3 / P1 ) - 10 log [(P2 + P3) / P3]
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5/13/10 Dr. Joseph C. 9.1 1414 LE = LTAP + 10 log [P3 /( P2 +P3)] = LTAP - L’TAP In the ideal case, P2 +P3 = P1, so that L’TAP = tap loss when excess loss is zero, but the splitting ratio is unchanged. Thus, when losses are present in the coupler LTAP = L’TAP + LE
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5/13/10 Dr. Joseph C. 9.1 1515 9.1.1 Duplexing Network Duplexing means simultaneous transmission in both directions through the fiber.
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chapter 9 - THE FIBER FORUM Fiber Optic PRESENTED BY Click...

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