When the input and output power in an optical fiber is 120μW & 3μW respectively and the length of the fiber is 8 km. What is the signal attenuation per km for the fiber?

Correct Answer: 2dB/km
Signal attenuation per unit length is given by αdBL = 10 log10Pi / Po αdBL = 16 dB αdB = 16 dB/L = 2dB/km.