(1) IR absorption

Light absorption of optical fiber in the IR range is attributable to the molecular vibration (lattice vibration) of SiO2 (IR absorption or molecular vibration absorption).

(2) UV absorption

Light absorption of optical fiber in the UV range is due to the energy band transition of SiO2 (UV absorption or electron transition absorption).

(3) Rayleigh scattering

The Rayleigh scattering is light scattering by a particle smaller than an incident light wavelength. A random density fluctuation, yielded in fused silica glass during the manufacturing process and fixed after, may cause the Rayleigh scattering. The density fluctuation yields the local fluctuation of refractive index, which scatters light in all directions. The loss by Rayleigh scattering is proportional to λ−4, therefore is larger for light with relatively shorter wavelength. The scattering loss is inherent to a fiber, and determines the minimum value of fiber loss.