1. Attenuation:
● Attenuation is the loss of signal strength in
networking cables or connections.
● It limits the link length.
● Attenuation in optical fibre take place due to
elements like coupler ,splices,connectors and fibre
itself.
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2. Types of Attenuation:
Absorption Loss:
●Caused by the fibre itself or by impurities in the fiber, such as water and metals.
Scattering Loss:
●Arise from microscopic variations in the material density, from compositional fluctuations
and from structural defects occurring during fiber manufacture.
Bending loss:
●Loss induced by physical stress on the fibre.
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3. Absorption:
•Absorption is a loss mechanism related to material
composition and fiber fabrication process.
•This results in the dissipation of optical power as heat
in the waveguide.
•Absorption is basically of two types:
1)Intrinsic Absorption.
2)Extrinsic Absorption.
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4. INTRINSIC ABSORPTION :
➔ Intrinsic absorption in the ultraviolet region is caused by
electronic absorption bands.
➔ The main cause of intrinsic absorption in the infrared region
is the characteristic vibration frequency of atomic bonds.In
silica glass, absorption is caused by the vibration of silicon-
oxygen (Si-O) bonds
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5. EXTRINSIC ABSORPTION:
➔ It is caused by impurities introduced into the fiber
material during manufacture – Iron, nickel, and
chromium
➔ It is caused by the electronic transition of metal ions
from one energy level to other.
➔It also occurs due to Hydroxyl ions(OH
-) into the fiber
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7. BENDING LOSS:
•Bending the fiber also
causes attenuation.
•Bending loss is classified
according to the bend radius
of curvature:
•Microbend loss.
•Macrobend loss.
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8. MICROBEND LOSS:
•Microbends are small microscopic bends of the fiber axis
that occur mainly when a fiber is cabled.
•Microbend losses are caused by small discontinuities or
imperfections in the fiber.
•Uneven coating applications and improper cabling
procedures increase microbend loss.
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9. MACROBEND LOSS:
•Macrobend losses are observed
when a fiber bend's radius of
curvature is large compared to the
fiber diameter.
•As the radius of curvature decreases,
the loss increases.
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10. Signal Distortion/Dispersion in Fibers
● Optical signal weakens from attenuation mechanisms and
broadens due to distortion effects.
● Eventually these two factors will cause neighboring pulses
to overlap.
● After a certain amount of overlap occurs, the receiver can no
longer distinguish the individual adjacent pulses and error arise
when interpreting the received signal.
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12. Intermodal Dispersion
● Intermodal distortion appears only in multimode fibers.
● This signal distortion mechanism is a result of each mode having
a different value of the group velocity at a single frequency.
● The amount of spreading that occurs in a fiber is a function of
the number of modes propagated by the fiber and length of the
fiber
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13. Intramodal Dispersion or Chromatic Dispersion
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Material Dispersion:
●This refractive index property causes a wavelength
dependence of the group velocity of a given mode; that is,
Pulse spreading occurs even when different wavelength
follow the same path.
●The refractive index of the material varies as a function of
wavelength
14. Intramodal Dispersion or Chromatic Dispersion
Waveguide Dispersion:
● It causes pulse spreading because only part of the optical
power propagation along a fiber is confined to core.
● Dispersion arises because the fraction of light power
propagating in the cladding travels faster than the light
confined to core.
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