1. OPTICAL FIBRE CABLE
An optical fiber cable is a cable containing one or more optical fibers.
The optical fiber elements are typically individually coated with plastic
layers and contained in a protective tube suitable for the environment
where the cable will be deployed.
DESIGN:
Optical fiber consists of a core and a cladding layer, selected for total
internal reflection due to the difference in the refractive index between
the two. In practical fibers, the cladding is usually coated with a layer of
acrylate polymer or polyimide. This coating protects the fiber from
damage but does not contribute to its optical waveguide properties.
A critical concern in outdoor cabling is to protect the fiber from
contamination by water. This is accomplished by use of solid barriers
such as copper tubes, and water-repellent jelly or water-absorbing
powder surrounding the fiber.
Finally, the cable may be armored to protect it from environmental
hazards, such as construction work or gnawing animals. Undersea cables
are more heavily armored in their near-shore portions to protect them
from boat anchors, fishing gear, and even sharks, which may be attracted
to the electrical power that is carried to power amplifiers or repeaters in
the cable.
CABLE TYPES:
OFC: Optical fiber, conductive
OFN: Optical fiber, nonconductive
OFCG: Optical fiber, conductive, general use
OFNG: Optical fiber, nonconductive, general use
OFCP: Optical fiber, conductive, plenum

2. OFNP: Optical fiber, nonconductive, plenum
OFCR: Optical fiber, conductive, riser
OFNR: Optical fiber, nonconductive, riser
OPGW: Optical fiber composite overhead ground wire
ADSS: All-Dielectric Self-Supporting
DATA TRANSMISSION:
Data transmission fiber optics, simply put, is the sending and receiving
of data from point-to-point via a network, thus the fundamental function
of all fiber systems from small to large. Data transmission requirements
range from very simple cables connecting servers or storage arrays
inside a network or telecommunications system, to large multi-fiber
distribution cables supporting intra-building connectivity and beyond.
For smaller, localized data transmission applications, a multitude of
products are available to move data from place to place. Primarily
multimode, these applications use single fibers to move multiple signals
over distances, usually less than 300 meters. Depending on the particular
application or system requirement, data transmission cabling can take
many forms from basic simplex (SX) or duplex (DX) cable assemblies
to ribbon fiber distribution cables, and various combinations of
customized products.
In larger data transmission applications, data transmission can be
multimode, single mode, or a combination of the two, depending on
bandwidth and transmission distance requirements. These applications
generally use a higher volume or longer lengths of cabling, or in some
case both, supporting data centers, building-to-building, campuses, and
carrier network communications.
PRINCIPLE OF OPERATION:
An optical fiber is a cylindrical dielectric waveguide (nonconducting
waveguide) that transmits light along its axis, by the process of total
internal reflection. The fiber consists of a core surrounded by a cladding
layer, both of which are made of dielectric materials. To confine the
optical signal in the core, the refractive index of the core must be greater
than that of the cladding.

3. Index of refraction
The index of refraction is a way of measuring the speed of light in a
material. Light travels fastest in a vacuum, such as outer space. The
speed of light in a vacuum is about 300,000 kilometers (186,000 miles)
per second. Index of refraction is calculated by dividing the speed of
light in a vacuum by the speed of light in some other medium. The index
of refraction of a vacuum is therefore 1, by definition. The typical value
for the cladding of an optical fiber is 1.52. The core value is typically
1.62. The larger the index of refraction, the slower light travels in that
medium.
Total internal reflection
When light traveling in an optically dense medium hits a boundary at a
steep angle (larger than the critical angle for the boundary), the light will
be completely reflected. This is called total internal reflection. This
effect is used in optical fibers to confine light in the core. Light travels
through the fiber core, bouncing back and forth off the boundary
between the core and cladding. Because the light must strike the
boundary with an angle greater than the critical angle, only light that
enters the fiber within a certain range of angles can travel down the fiber
without leaking out. This range of angles is called the acceptance cone
of the fiber. The size of this acceptance cone is a function of the
refractive index difference between the fiber's core and cladding.
Multi-mode fiber
Fiber with large core diameter (greater than 10 micrometers) may be
analyzed by geometrical optics. Such fiber is called multi-mode fiber,
from the electromagnetic analysis. In a step-index multi-mode fiber, rays
of light are guided along the fiber core by total internal reflection. Rays
that meet the core-cladding boundary at a high angle greater than the
critical angle for this boundary, are completely reflected. The critical
angle (minimum angle for total internal reflection) is determined by the
difference in index of refraction between the core and cladding
materials. Rays that meet the boundary at a low angle are refracted from
the core into the cladding, and do not convey light and hence
information along the fiber.

4. Single-mode fiber
Fiber with a core diameter less than about ten times the wavelength of
the propagating light cannot be modeled using geometric optics.
The electromagnetic analysis may also be required to understand
behaviors such as speckle that occur when coherent light propagates in
multi-mode fiber. As an optical waveguide, the fiber supports one or
more confined transverse modes by which light can propagate along the
fiber. Fiber supporting only one mode is called single-mode or mono-
mode fiber. The most common type of single-mode fiber has a core
diameter of 8–10 micrometers and is designed for use in the near
infrared. The mode structure depends on the wavelength of the light
used, so that this fiber actually supports a small number of additional
modes at visible wavelengths. Multi-mode fiber, by comparison, is
manufactured with core diameters as small as 50 micrometers and as
large as hundreds of micrometers.
Special-purpose fiber
Some special-purpose optical fiber is constructed with a non-cylindrical
core and/or cladding layer, usually with an elliptical or rectangular
cross-section. These include polarization-maintaining fiber and fiber
designed to suppress whispering gallery mode propagation.
Disadvantages of Optical fibres:
Price - Even though the raw material for making optical fibres, sand, is
abundant and cheap, optical fibres are still more expensive per metre
than copper. Although, one fibre can carry many more signals than a
single copper cable and the large transmission distances mean that fewer
expensive repeaters are required.
Fragility - Optical fibres are more fragile than electrical wires.
Affected by chemicals - The glass can be affected by various chemicals
including hydrogen gas (a problem in underwater cables.)
Opaqueness - Despite extensive military use it is known that most fibres
become opaque when exposed to radiation.
Requires special skills - Optical fibres cannot be joined together as a
easily as copper cable and requires additional training of personnel and
expensive precision splicing and measurement equipment.

5. Advantages Of Fiber Optics
Immunity to Electromagnetic Interference
Data Security
Non Conductive Cables
Eliminating Spark Hazards
Ease Of Installation
High Bandwidth Over Long Distances
Uses of Optical Fibres
Until the optical fibre network was developed, telephone calls were
mainly sent as electrical signals along copper wire cables. As demand
for the systems to carry more telephone calls increased, simple copper
wires did not have the capacity, known as bandwidth, to carry the
amount of information required.
Systems using coaxial cables like TV aerial leads were used but as the
need for more bandwidth grew, these systems became more and more
expensive especially over long distances when more signal regenerators
were needed. As demand increases and higher frequency signals are
carried, eventually the electronic circuits in the regenerators just cannot
cope.
Optical fibres offer huge communication capacity. A single fibre can
carry the conversations of every man, woman and child on the face of
this planet, at the same time, twice over. The latest generations of optical
transmission systems are beginning to exploit a significant part of this
huge capacity, to satisfy the rapidly growing demand for data
communications and the Internet.
The main advantages of using optical fibres in the communications
industry are:
- A much greater amount of information can be carried on an optical
fibre compared to a copper cable.
- In all cables some of the energy is lost as the signal goes along the
cable. The signal then needs to be boosted using regenerators. For
copper cable systems these are required every 2 to 3km but with optical
fibre systems they are only needed every 50km.

6. - Unlike copper cables, optical fibres do not experience any electrical
interference. Neither will they cause sparks so they can be used in
explosive environments such as oil refineries or gas pumping stations.
- For equal capacity, optical fibres are cheaper and thinner than copper
cables which makes them easier to install and maintain.