07-05-2014, 04:22 PM
PRESENTATION ON lOSSES in fiber optics
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Losses in fiber optics:
There are different reasons for light losses which may occur during transmission of light signal inside the fiber or during the interconnection process of two fiber.
(I)Absorption lossesMaterial absorption losses)
Light travels best in clear substances.Impurities such as metal particles or moisture in the fiber can block some of the light energy, it absorbs the light and dissipate it in the form of heat energy, which caused absorption loss.
The composition of the material and the fabrication process of the fiber gives rise to material absorption. This results in the mechanism where optical power transmitted is lost as heat in the waveguide.
The material absorption is of two types.
(a) Intrinsic absorption
(b) Extrinsic absorption
Intrinsic absorption:
Intrinsic absorption is caused by basic fiber material properties.
If an optical fiber were absolutely pure, with no imperfections or impurities, then all absorption would be intrinsic.
Absorption occurs when a photon interacts with an electron in the valence band and excites it to higher energy level.
Intrinsic absorption is very strong in the short wavelength ultraviolet portion of electromagnetic spectrum.
Bending lossesRadiative losses)
Bending losses occur whenever an optical fiber undergoes a bend of finite radius of curvature. This is one of the major causes of total attenuation that light experiences while propagating through an optical fiber.
Fibers can be subject to two types of bends, so, there are mainly two types of bending losses.
(a) Macro bending losses.
(b) Micro bending losses.
Microbending losses:
Microbending loss is caused by the micro deformation of the fiber axis. Microbends do not have regular shapes or distributions along the fiber.
Light travels along straight segment of a fiber, light beam meets these imperfections and gets deflected.
The beam that initially travels at the critical propagation angle changes its angle of propagation after reflection at these imperfections. So, condition of total internal reflection is not met and a portion of the beam will be refracted and will leak out of the core.