Light Attenuation

• The attenuation of light refers to the reduction in it’s intensity as it travels through a medium due to absorption or scattering of photons.
• Primary causes: photoelectric effect, Compton scattering and pair production(for photon energies above 1.022 MeV)

Light travelling in transparent materials is attenuated according to:

$I = I_{o} \, e^{- \mu x}$, where
I and I_o are the final and initial intensity respectively,
x is the distance (in km),
μ is the attenuation coefficient, expressed in km^-1

This can be applied to optical firbres. Absorption of infrared occurs when it travels through glass, but less for longer wavelengths than shorter ones. As well as loss due to absorption by impurity atoms in the glass, scattering of the radiation at imperfect joings in the fibre also adds to the attenuation. Attenuated pulses have their size and shape restored by the use if regenerators at intervals along the optical cable.

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