Question

Engineers designing a fiber-optic communications link decide that as soon as the transmitted light intensity falls to 0.1% of its orginal value, an amplifier must be inserted in the line to restore the intensity to its orginal value. How many amplifers are required in a 1200 km line if the attenuation in dB/km of the glass is (a) 100 (b) 10 (c) 1 (d) 0.1?

Answer 1

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A signal getting attenuated by 0.1% means a 20dB attenuation. Thus, for every 20dB attenuation, an amplifier is to be inserted.

(a) Total attenuation = 100*1200 dB.

Number of amps needed = 100*1200/20 = 6000

(b) Total attenuation = 10*1200 dB.

Number of amps needed = 10*1200/20 = 600

(c) Total attenuation = 1*1200 dB.

Number of amps needed = 1*1200/20 = 60

(d) Total attenuation = 0.1*1200 dB.

Number of amps needed = 0.1*1200/20 = 6