There are several sources of attenuation in optical fibers. In addition to losses due to mechanical variations in the fiber dimensions, there will be losses due to:

• Rayleigh scattering ... Can scatter light rays in many directions, causing loss of optical power. Generally, microscopic irregularities in the index of refraction of the glass represent the most important mechanism for attenuation in modern fiber. Rayleigh scattering is wavelength dependent (proportional to 1/l⁴) and is thus less significant at longer wavelengths.
• Absorption ... The attenuation in silica, can be significant at the short-wavelength end, due to UV (electronic) absorption and at the long-wavelength (infrared) end, due to multiphoton (atomic vibrational) absorption. In addition, unwanted impurities and intentional dopants in the fiber, absorb optical energy around specific wavelengths. State-of-the-art manufacturing methods have reduced impurity levels to the point that their effect is almost insignificant.
• Bending ... Microbending, the result of microscopic imperfections in the fiber geometry, is caused by the manufacturing process or mechanical stress. Macrobending occurs when the fiber is bent into a larger, visible curvature. In both cases, light rays hit the core-cladding interface with angles greater than the critical angle and optical energy is lost into the cladding. Bend sensitivity of fiber includes the attenuation losses from both macro and microbending. It can be given in terms of dB/km of loss for a particular bend radius and wavelength. Proper selection of coating materials and optical properties can dramatically improve microbending effects on transmission.

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