Calculate the maximum length of an optical fibre that exhibits 0.8dB/km attenuation if the optical output is 10mW and the power launched at the input is 150mW. [Hint: Loss, L=10 log (P_{o}/P_{i})]
Ans:
Given
P_{o}=10mW
P_{i}=150mw
We have
Loss, L=10 log (P_{o}/P_{i})
Substituting for P_{o }and P_{i,}
_{ }L= -11.76dB
For 1km , the loss is 0.8dB.
Let the length of the cable be x km. Then, for x kms, the loss is -11.76dB.
Solving for x, we have
x= (11.76 x 1)/0.8
=15km
i.e the length of the cable is 15km approximately.