Given Information:
Input Power = Pin = 120 W
Output Power = Pout = 3 W
Length of fiber = 8 km and 10 km
Required Information:
a) Overall signal attenuation in dB and dB/km = ?
b) Overall signal attenuation in dB with 10 km and 9 splices adding 0.5 dB of attenuation = ?
Answer:
a) α ≈ 16 dB and α = 2 dB/km
b) α = 24.5 dB
Explanation:
a) Overall signal attenuation in dB
The signal attenuation is the log of output and input power ratio
α = 10*log(Pout/Pin)
α = 10*log(3/120)
α = 16.02 ≈ 16 dB
Divide overall attenuation by the entire length to get per km attenuation
α = 16/8 = 2 dB/km
b) Overall signal attenuation in dB with 10 km and 9 splices adding 0.5 dB of attenuation
Since we know the rate of per km attenuation, we will multiply that with the entire length
2 dB/km*10 km = 20 dB
Now calculate the attenuation due to splices
There are 9 splices and each splice causes 0.5 dB attenuation per km so
9*0.5 dB = 4.5 dB
So the total attenuation is
α = 20 dB + 4.5 dB
α = 24.5 dB
