What Is the Working Principle Of Fiber Optic Cables

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For understanding the working principle of
optical fiber cable clearly, we first further learn the components of an
optical fiber cable.

 

Components of Fiber Cable

 

A fiber optic cable can be divided into
three parts. It is a coaxial cable, and the center most part is called the core
which is made out of a very clear glass tube and carries the information. The
plastic covering above it which causes the reflection of light signals is
called the cladding and the sheathing that protects the optical fiber is called
the coating. In a single mode fiber, the core is about 5-10 microns in
diameter. A dimension of 5 to 10 microns is equivalent to the millionth of a
meter. That small is the core of an optical fiber.

 

The reason why core is made out of glass is
that, glass is incredibly pure so that, even though it is several miles long,
light can still make it through. The glass is drawn into a very thin strand,
with a thickness comparable to that of a human hair. The glass strand is then
coated in two layers of plastic. So fiber optic cable is also called glass
fiber cable.

 

In order for the finished cable to transmit
data signals, it needs to be connected to the three other main components of a
fiber optic system, named optical transmitter, optical receiver and optical
regenerator.

 

Optical Transmitter

 

Optical transmitter, a device which
converts electrical and analog signals into either On-Off or Linear modulating
light signals, then releases that data into the fiber optic cable. The pattern
of light waves forms a code that carries a message. The cable then relays the
data emitted by the optical transmitter to the optical receiver, which accepts
the light signal and reformats the data into its original form.

 

Optical Receiver

 

The receiver is essentially performing the
opposite function of the transmitter. Optical receivers receive the light
signal from the fiber optic able and turn it back into information that a
computer or television know how to understand and use. It then sends the
decoded signal to the computer or television.

 

Optical Regenerator

 

Sometimes a light signal must travel
through a fiber optic cable over a very long distance. Although signal
degradation is minimal in a fiber
optic patch cable, some
degradation does occur. When a cable covers a long distance, optical
regenerators are placed at certain intervals along the cable. Optical
regenerators are fibers that have been treated with a laser. The molecules in
the fiber allow the signal traveling through the fiber optic cable to take on
laser properties themselves, which strengthens the light signal. Optical
regenerators essentially strengthen the light signal that is traveling through
a fiber optic cable.

 

Working Principle of Fiber Optic Cable

 

The light travels through the glass strands
and continuously reflects off of the inside of the mirrored plastic coatings in
a process known as “Total Internal Reflection”.

 

When light travels from a medium of lower
refractive index to that of a higher refractive index, it bends towards the
normal. The normal is a line that is perpendicular to the interface of two
mediums. However, when light travels from a medium of higher refractive index
to that of a lower refractive index, it bends away from the normal.

 

The angle made by the incident ray to the
normal is called the angle of incidence and the angle made by the refracted ray
with the normal at the point of incidence in the other medium is called the
angle of refraction. Now, consider that light is traveling from a medium with
higher refractive index to that of a lower refractive index. As the angle of
incidence increases, the angle of refraction also increases. Now, if the angle
of incidence is increased to a point that the angle of refraction becomes
perpendicular to the angle of refraction, almost parallel to the interface of
the two media, then this particular of angle of incidence is called the
critical angle. If the angle of incidence is further increased beyond this
angle of incidence, then the refracted light will be returned to the same
medium, reflected. This is the process of total internal refraction.

 

What happens in fiber optics is that the
light is sent at such an angle almost parallel to the optical fiber, it goes
through the process of total internal reflection and travels through hundreds
of kilometers. Besides, as we all know that the highest speed of any form of
energy is that of light energy. So, it has to be the fastest way of
communication. Light gets reflected at the walls of the pure glass and hence
travels through hundreds of kilometers.

 

In order for optical fibers to transmit
data over long distances, they need to be highly reflective. On their way to
being spooled, newly-pulled glass fibers pass through coating cups and
ultraviolet ovens, which respectively apply and then cure the thin plastic
buffer coating that creates a mirror effect within the fiber.

 

The typical three types of fiber optic
cables, including multimode fiber optic cable, single mode cable and plastic
optical fiber cable (POF), are all adaptable to the basic structure and working
principle.