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Optical Fibre - Coggle Diagram
Optical Fibre
Types of Dispersion
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Intermodal Dispersion
When an optical pulse is launched into a fiber,the optical power in the pulse is distributed over all of the modes of the fiber.
-Each of the modes that can propagate in a multimode fiber travels at a slightly different velocity.
Chromatic Dispersion
Chromatic dispersion is actually the sum of 2 components: material dispersion and waveguide dispersion.
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Step Index OF
When an optical pulse is launched into a SI fiber, the propagation velocity of the pulse is highly dependent on the incident angle. This is problematic for high-speed optical communication as the incident pulse shape is degraded at the output.
Graded Index OF
GI fiber was introduced in order to overcome this limitation of SI fiber. A graded index is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the optical axis of the fiber.
Single Mode OF
The use of single-mode fibers in an optical transmission line fundamentally eliminates signal distortions due to modal delay, and thus single-mode fibers have now become the most widely used type of optical fibers in optical communications.
Loss Mechanism
Rayleigh Scattering — Microscopic-scale variations in the index of refraction of the core material can cause considerable scatter in the beam, leading to substantial losses of optical power.
Absorption — Current manufacturing methods have reduced absorption caused by impurities (most notably water in the fiber) to very low levels. Within the bandpass of transmission of the fiber, absorption losses are insignificant.
Bending — Manufacturing methods can produce minute bends in the fiber geometry. Sometimes these bends will be great enough to cause the light within the core to hit the core/cladding interface at less than the critical angle so that light is lost into the cladding material.
Basic Working Principle
Based on TIR
Occurence of total internal reflection for rays approaching the core-cladding interface at angles exceeding the critical angle for the interface.
Basic Structure
The basic structure of an optical fiber consists of three parts; the core, the cladding, and the coating or buffer. The core is a cylindrical rod of dielectric material. Dielectric material conducts no electricity. Light propagates mainly along the core of the fiber. The core is generally made of glass. The core is described as having a radius and an index of refraction n1. The core is surrounded by a layer of material called the cladding.
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Classification of Fibre
Optical fibre can be classififed according to its core-cladding size, fibre materials, refractive index profile and propagation path.
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The modes that enter at sharp angles (high-order modes). It take much longer to travel through the fiber than the low-order modes and therefore contribute to modal dispersion. One way to reduce modal dispersion is to use graded-index fiber.
With a graded-index fiber, the light follows a more curved path. The high-order modes spend most of the time traveling in the lower-index cladding layers near
the outside of the fiber. These lower-index core layers allow the light to travel faster than in the higher-index center layers.
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