Fiber optic networks transmit light through optical fibers to communicate over long distances at high bandwidth. An optical fiber consists of a cylindrical glass core surrounded by a cladding layer of glass or plastic with a lower refractive index. This structure allows light to propagate along the core through total internal reflection. Fibers have a small single-mode core or larger multimode core. Single-mode fiber has lower attenuation over long distances while multimode can transmit more data over shorter runs.

1. NETWORK STRUCTURE

2. FIBER OPTIC NETWORK
 An optical fiber (or optical fibre) is a flexible,
transparent fiber made by drawing glass (silica) or
plastic to a diameter slightly thicker than that of
a human hair. Optical fibers are used most often as
a means to transmit light between the two ends of
the fiber and find wide usage in fiber-optic
communications, where they permit transmission
over longer distances and at
higher bandwidths (data rates) than wire cables.

4.  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 of (a) and
an index of refraction n1. The core is surrounded by
a layer of material called the cladding.
BASIC STRUCTURE OF AN OPTICAL FIBER

5.  The cladding layer is made of a dielectric material with
an index of refraction n2. The index of refraction of the
cladding material is less than that of the core material.
The cladding is generally made of glass or plastic. The
cladding performs the following functions:
 Reduces loss of light from the core into the surrounding
air
 Reduces scattering loss at the surface of the core
 Protects the fiber from absorbing surface contaminants
 Adds mechanical strength
 For extra protection, the cladding is enclosed in an
additional layer called the coating or buffer.
The coating or buffer is a layer of material used to
protect an optical fiber from physical damage. The
material used for a buffer is a type of plastic.

7.  Single Mode fiber optic cable has a small
diametric core that allows only one mode of light to
propagate. Because of this, the number of light
reflections created as the light passes through the
core decreases, lowering attenuation and creating
the ability for the signal to travel faster, further. This
application is typically used in long distance, higher
bandwidth runs by companies, and Colleges and
Universities.

8.  Multimode fiber optic cable has a large diametric
core that allows multiple modes of light to
propagate. Because of this, the number of light
reflections created as the light passes through the
core increases, creating the ability for more data to
pass through at a given time. Because of the high
dispersion and attenuation rate with this type of
fiber, the quality of the signal is reduced over long
distances. This application is typically used for short
distance, data and audio/video applications in
LANs.

10.  For an optical fiber, a step-index profile is a
refractive index profile characterized by a uniform
refractive index within the core and a sharp
decrease in refractive index at the core-cladding
interface so that the cladding is of a higher
refractive index.
 In fiber optics, a graded-index fiber is an optical
fiber whose core has a refractive index that
decreases with increasing radial distance from the
fiber axis (the imaginary central axis running down
the length of the fiber).

12. SATELLITE NETWORKS
 In satellite communication, signal transferring
between the sender and receiver is done with the
help of satellite. In this process, the signal which is
basically a beam of modulated microwaves is sent
towards the satellite. Then the satellite amplifies the
signal and sent it back to the receiver’s antenna
present on the earth’s surface. So, all the signal
transferring is happening in space. Thus this type of
communication is known as space communication.

14. CELLULAR NETWORK
 Cell site is a geographical area that is circular in
shape and caters to cellular phones insides its
defined physical boundary.
 A cellular network consists of overlapped cells so
that a larger area with low probability of call
dropping may be provided.
 The overlapping in the structure ensures that the
call is kept uninterrupted when the user changes
his position from one cell site to the other.