Question

A fiber-optic communication link is designed for opeation at 10Mb/s. The source is a 1mW AIGaAs diode laser operating at 0.87 um. the requierd BER=10 -9. The fiber is made of 1km segments each with attenuation 3.5 dB/km. Connectors bewteen segments have a loss of 2 dB each and input and output couplers each introduce a loss of 2 dB. The safety margin is 6 dB. Two receivers are available, a Si pin photodiode receiver and a SiAPD reveiver. Determine the maximum length of the link for each reveiver.

Answer 1

4dB will be the loss, due to the presence of the input and output couplers. and it will be there no matter what. So we have to take the length of the wire in such a way that the loss is only 2dB at max (since the safety margin is 6dB). Let the length of the wire be x. Then we can write,

Hence the maximum length possible for the set of receivers is 570m, so as to have a 6dB saftery margin.