(i) the overall signal attenuation or loss, in decibels through the fiber assuming there is no connector or splicer. (ii) The signal attenuation per kilometer for the fibers.

A. Overall Signal attenuation or loss in decibels through the fiber assuming there are no connectors or splices is given by,

Signal attentuation $(\alpha _{db}L) = 10log_{10}Pi/Po \\ \ \ \ \ \ \ \ \ \ \ \ = 10log_{10}(120\times10^{-6} / 3 \times 10^{-6}) \\ \ \ \ \ \ \ \ \ \ \ \ = 10 log_{10}40 \\ \ \ \ \ \ \ \ \ \ \ \ = 16.0 dB$

B.The signal attenuation per Km for the fibers is given by,

$\alpha_{db}L = 16.0 dB \\ As L = 8km \\ \therefore \alpha_{db} = 16.0/8 \\ \alpha_{db} = 2.0 dB/km $