In fiber-optic transmission, what is attenuation?

• A. Signal loss over distance
• B. Signal amplification
• C. Dispersion broadens pulses
• D. Reflection loss

Answer: (A)

Attenuation is the decrease in optical signal power as light travels through the fiber. This loss comes from absorption by the glass, scattering from tiny imperfections, and bending losses when the fiber is curved. It’s usually expressed in decibels per kilometer, showing how much power is lost for each kilometer of travel. This concept matters because as the signal travels longer distances, attenuation reduces it to levels the receiver can’t detect without amplification or regeneration. It’s different from dispersion, which is about pulse broadening in time, and from reflection loss at interfaces. It’s also the opposite of amplification, which increases signal strength. For example, a fiber with 0.2 dB per kilometer would lose about 2 dB over 10 kilometers, reducing the received power accordingly.