TOTAL INTERNAL REFLFECTION

An optical fiber is composed of a very thin glass rod which is divided into two concentric regions, called the core and cladding.

A single finer can then be coated with a protective plastic called a buffer and strength materials, such as Kevlar and polymers Optical fibers are based entirely on the principle of total internal reflection.

The Structure of an Optical Fiber

Core, Cladding ,the Buffer coating, Cable jacket, Rip cord,

Aramid Yarn, Central Strength Member, Gel Compound

LIGHT TRANSMISSION IN FIBER

Fiber transmit using light pulses, It transmits at the speed of

light The fiber core and cladding have different chemical

composition which determines their index of refraction.

The cladding with its lower index reflects the light back into

the core. This effect helps guide the light down the fiber.

The velocity of light in the glass is different from the velocity

of light in a vacuum. This ratio is known as the index of

refraction

NUMERIC APERTURE

The numerical aperture (NA) of an optical fiber

defines the range of angles over which the system

can accept light. This is called the core of acceptance

If light enters the fiber at greater than the critical

angle, it is Refracted and not captured by the core

PropagationThis Refers to light rays entering the fiber at

different angles and travelling different paths or modes down the fiber

resulting in different arrival times. If light enters the fiber at greater than the critical angle, it is

refracted and not captured

by the core.

ATTENUATIONThis is referred to as the loss of signal over distance. Attenuation is

the reduction of signal strength or light power over the length of

the light-carrying medium

SCATTERINGRayleigh Scattering:

Light energy is scattered in all directions, causing loss of

power. A small percentage of light gets scatteredback to

the source

Absorption, scattering, reflection, refraction,

and injection loss all add up to build attenuation. These

phenomenon are inherent to the fiber

DISPERSIONDispersion is not a loss of light, it is a distortion of the signal.

Dispersion is defined as the spreading or broadening of light pulses as they travel through a fiber.

There are two types of dispersion in optical fibers

Chromatic dispersion (CD) Polarization Mode dispersion (PMD)

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