Attenuation
The loss of optical power or signal strength as light propagates through a medium or optical fiber.
Governing formula
α = (10 / L) log10(P_in / P_out)
SI unit
dB/km
In depth
Caused by Rayleigh scattering, material absorption, and micro-bending losses. Modern silica fibers achieve ultralow attenuation of ~$0.2 dB/km$ at 1550 nm.
Examples in the real world
Using erbium-doped fiber amplifiers (EDFAs) every 80 km along undersea optical cables to boost attenuated signals.