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OPTICAL FIBER - Coggle Diagram
OPTICAL FIBER
Dispersion
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Modal Dispersion
Time delays occurs among different modes, with each mode exiting the fibre at different times.
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The degree of Pulse spreading in multimode fibre
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Intramodal DIspersion
CD+MD+WD,
-The magnitude of pulse spreading increase with distance down the fibre.
-The magnitude of the pulse spread is also dependent on the source linewidth
Acceptance Angle
The acceptance angle of an optical fiber is defined based on a purely geometrical consideration (ray optics: it is the maximum angle of a ray (against the fiber axis) hitting the fiber core which allows the incident light to be guided by the core
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To capture & ensure that rays entering the fibre end surface remain inside the core, the rays must approach the fibre end at angles less than the acceptance angle for the fibre
The acceptance angle determines the numerical aperture (NA) of the fibre & is given by
Classification of fibre
Core-cladding size
The function of the cladding is to provide a lower refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fiber. :star: size of typical human hair
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Fibre materials
Optical fibre can be made up of several types of fibre materials such as plastic-class silica(PCS), photonic crystal, all-plastic, all-glass etc
PCS fibers in general have significantly lower performance characteristics, particularly higher transmission losses and lower bandwidths, than all-glass fibers.
A photonic crystal fiber (also called holey fiber, hole-assisted fiber, microstructure fiber, or microstructured fiber) is an optical fiber which obtains its waveguide properties not from a spatially varying glass composition but from an arrangement of very tiny and closely spaced air holes which go through the whole length of fiber.
Photonic crystal is a low-loss periodic dielectric medium constructed using a periodic array of microscopic air holes that run along the entire fiber length.
In PCFs, photonic crystals with photonic band gaps are constructed to prevent light propagation in certain directions with a certain range of wavelengths.
Contrary to normal fiber optics, PCFs use total internal reflection or light confinement in hollow core methods to propagate light. Light propagation in PCFs is far superior to standard fiber, which uses constant lower refractive index cladding.
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Propagation path
The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances.
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Basic Working principle
Occurence of total internal reflection for rays approaching the core-cladding interface at angles exceeding the critical angle for the interface.
When a ray of light is incident on the core of optical fiber at a small angles, it suffers refraction and strikes the core-cladding interface as the diameter of the fiber is very small hence the angle of incidence is greater than the critical angle
V-parameter
For single-mode operation, the normalizes frequency should be V<= 2.40
Normalized frequency of called V-parameter is given by
Attenuation
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defined as ratio of input (transmitted) optical power Pi into fiber to the output (received) power Po
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