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Optical Link Design



                                                                         Optical Link Design  269





























                      Figure 16.3. Receiver sensitivities as a function of bit rate. The Si
                      pin, Si APD, and InGaAs pin curves are for a 10  9  BER. The InGaAs
                      APD curve is for a 10  11  BER.

                      TABLE 16.2. Spreadsheet for Calculating a LAN Link Power Budget
                      Component/loss parameter   Output/sensitivity/loss  Power margin, dB

                      Coupled LED output              20dBm
                      pin sensitivity at 100Mbps      32dBm
                      Allowed loss [ 20   ( 32)]                           12
                      Source connector loss           0.7dB                11.3
                      2   Jumper connector loss       1.4dB                 9.9
                      Cable attenuation (160m)        0.4dB                 9.5
                      Receiver connector loss         0.7dB                 8.8 (final margin)



                      optical power loss that is allowed between the light source and the photo-
                      detector. In this case the allowable loss is

                                    P T   P S   P R   20dBm   ( 32dBm)   12dB

                      The final power margin is 8.8dB, which is a sufficient margin for this link.

          16.2.3. SONET/SDH link example
                      An engineer plans to design a 2.5-Gbps SONET OC-48 (or equivalently, an SDH
                      STM-16) link over a 30-km path length, as shown in Fig. 16.4. The basic question


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