[Solved] For a single mode optical fiber cable with attenuation of 0.25 dB/km, ...

For a single mode optical fiber cable with attenuation of 0.25 dB/km, the optical power (in dBm), 100 km away, from a 0.1 mW light source will be:

A. −10 dBm
B. −25 dBm
C. −30 dBm
D. −35 dBm

Solution:

Step 1: Convert source power to dBm

0.1 mW = 10^-1 mW

P = 10 log₁₀(0.1) = −10 dBm

Step 2: Calculate total attenuation

Attenuation = 0.25 dB/km × 100 km = 25 dB

Step 3: Calculate output power

Output power = −10 − 25 = −35 dBm

Final Answer: D. −35 dBm

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