CONTENT
• Important terms
• Optical fiber cable
• Applications
• Principle of operation
• Mechanism of attenuation
• Manufacturing
• Bibliography
IMPORTANT TERMS
Optical Fiber: An optical fiber (or fiber) is a glass or plastic fiber that carries
light along its length. Fiber optics is the overlap of applied science and
engineering concerned with the design and application of optical fibers.
Refraction: Refraction the change in direction of a wave due to a change in its
speed. This is most commonly observed when a wave passes from one medium
to another.
Reflection: Reflection is the change in direction of a wave front at an interface
between two different media so that the wave front returns into the same
medium from which it is originated
Scattering: Scattering is a general physical process where some forms of
radiation, such as light, sound, or moving particles, are forced to deviate from a
straight trajectory by one or more localized non-uniformities in the medium
through which they pass. In conventional use, this also includes deviation of
reflected radiation from the angle predicted by the law of reflection.
Attenuation: is the gradual loss in intensity of any kind of flux through a
medium. For instance, sunlight is attenuated by dark glasses, and X-rays are
attenuated by lead
Optical Fiber Cable (OFC)
An optical fiber (or fiber) is a glass or plastic fiber that carries light along its
length. Fiber optics is the overlap of applied science and engineering
concerned with the design and application of optical fibers. Optical fibers are
widely used in fiber-optic communications, which permits transmission over
longer distances and at higher bandwidths (data rates) than other forms of
communications. Fibers are used instead of metal wires because signals travel
along them with less loss, and they are also immune to electromagnetic
interference. Fibers are also used for illumination, and are wrapped in bundles
so they can be used to carry images, thus allowing viewing in tight spaces.
Specially designed fibers are used for a variety of other applications, including
sensors and fiber lasers. Light is kept in the core of the optical fiber by total
internal reflection. This causes the fiber to act as a waveguide. Fibers which
support many propagation paths or transverse modes are called multi-mode
fibers, while those which can only support a single mode are called single-
mode fibers. MMF generally has a larger core diameter, and is used for short-
distance communication links and for applications where high power must be
transmitted. Single-mode fibers are used for most communication links longer
than 550 meters. Joining lengths of optical fiber is more complex than joining
electrical wire or cable. The ends of the fibers must be carefully cleaved, and
then spliced together either mechanically or by fusing them together with ans
electric arc.Special connectors are used to make removable connection
APPLICATIONS
Optical Fiber Communication
Optical fiber can be used as a medium for telecommunication and networking
because it is flexible and can be bundled as cables. It is especially advantageous
for long-distance communications, because light propagates through the fiber
with little attenuation compared to electrical cables. This allows long distances
to be spanned with few repeaters. Fiber Optic Sensors
Fibers have many uses in remote sensing. In some applications, the sensor is
itself an optical fiber. In other cases, fiber is used to connect a non-fiber optic
sensor to a measurement system. Depending on the application, fiber may be
used because of its small size, or the fact that no electrical power is needed at
the remote location, or because many sensors can be multiplexed along the
length of a fiber by using different wavelengths of light for each sensor, or by
sensing the time delay as light passes along the fiber through each sensor.
Other Uses of Optical Fibers
>Fibers are widely used in illumination applications. They are used as light
guides in medical and other applications where bright light needs to be shown
on a target without a clear line-of-sight path.
>In some buildings, optical fibers are used to route sunlight from the roof to
other parts of the building (see non-imaging optics). Optical fiber illumination
is also used for decorative applications, including signs, art, and artificial
Christmas trees. Example; Swarovski boutiques use optical fibers to illuminate
their crystal showcases from many different angles while only employing one
light source.
>Optical fiber is an intrinsic part of the light-transmitting concrete building
product, LitraCon.
>Optical fiber is also used in imaging optics. A coherent bundle of fibers is
used, sometimes along with lenses, for a long, thin imaging device called an
endoscope, which is used to view objects through a small hole.
>In spectroscopy, optical fiber bundles are used to transmit light from a
spectrometer to a substance which can't be placed inside the spectrometer
itself, in order to analyze its composition.
> Optical fibers doped with a wavelength shifter are used to collect scintillation
light in physics experiments.
PRINCIPLE OF OPERATION
An optical fiber is a cylindrical dielectric waveguide (non- conducting
waveguide) that transmits light along its axis, by the process of total internal
reflection. The fiber core is surrounded by cladding layer
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 actual speed of light
in a vacuum is about 300 million meters (186 thousand 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 1.46. The core value is typically 1.48. The larger the index of refraction, the
slower light travels in that medium. From this information, a good rule of
thumb is that a signal using optical fiber for communication will travel at
around 200 million meters per second. Or to put it another way, to travel 1000
kilometers in fiber, the signal will take 5 milliseconds to propagate. Thus a
phone call carried by fiber between Sydney and New York, a 12000 kilometer
distance, means that there is an absolute minimum delay of 60 milliseconds(or
around 1/16th of a second) between when one caller speaks to when the other
hears. (Of course the fiber in this case will probably travel a longer route, and
there will be additional delays due to communication equipment switching and
the process of encoding and decoding the voice onto the fiber).
Total Internal Reflection
When light traveling in a dense medium hits a boundary at a steep angle
(larger than the "critical angle for the boundary"), the light will be completely
reflected. This effect is used in optical fibers to confine light in the core. Light
travels along the fiber bouncing back and forth off of the boundary.
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.
In simpler terms, there is a maximum angle from the fiber axis at which light
may enter the fiber so that it will propagate, or travel, in the core of the fiber.
The sine of this maximum angle is the numerical aperture (NA) of the fiber.
Fiber with a larger NA requires less precision to splice and work with than
fiber with a smaller NA. Single-mode fiber has a small NA.
MECHANISMS OF ATTENUATION
Attenuation is an important factor limiting the transmission of a digital signal
across large distances. Thus, much research has gone into both limiting the
attenuation and maximizing the amplification of the optical signal. Empirical
research has shown that attenuation in optical fiber is caused primarily by
both scattering and absorption.
Light Scattering
The propagation of light through the core of an optical fiber is based on total
internal reflection of the light wave. Rough and irregular surfaces, even at the
molecular level, can cause light rays to be reflected in random directions. This
is called diffuse reflection or scattering, and it is typically characterized by a
wide variety of reflection angles.
MANUFACTURING
Materials
Glass optical fibers are almost always made from silica, but some other
materials, such as fluorozirconate, fluoroaluminate and chalcogenide glasses,
are used for longer wavelength infrared applications. Like other glasses, these
glasses have a refractive index of about 1.5. Typically the difference between
core and cladding is less than one percent.
Silica
In the near-infrared (near IR) portion of the spectrum, particularly
around 1.5 m, silica can have extremely low absorption and scattering
losses of the order of 0.2 dB/km. A high transparency in the 1.4um
region is achieved by maintaining a low concentration of hydroxyl
groups (OH). Alternatively, a high 09 concentration is better for
transmission in the ultraviolet (UV) region.
Process
Standard optical fibers are made by first constructing a large-
diameter preform, with a carefully controlled refractive index profile,
and then pulling the preform to form the long. thin optical fiber. The
preform is commonly made by three chemical vapor deposition
methods: inside deposition, outside vapor deposition, and vapor axial
deposition.
With inside vapor deposition, the preform starts as a hollow glass
tube approximately 40 centimeters (16 in) long, which is placed
horizontally and rotated slowly on a lathe. Gasses such as silicon
tetrachloride (SiCl4) or germanium tetrachloride (GeCl4) are injected
with oxygen at the end of the tube. The gasses are then heated by
means of an external hydrogen burner, bringing the temperature of
the gas up to 1900 K (1600 C, 3000 F), where the tetrachloride's react
with oxygen to produce silica or Germania (germanium dioxide)
particles. When the reaction conditions are chosen to allow this
reaction to occur in the gas phase throughout the tube volume, in
contrast to earlier techniques where the reaction occurred only on the
glass surface, this technique is called modified chemical vapor
deposition.
Coatings
Fiber optic coatings are UV-cured urethane acrylate composite materials
applied to the outside of the fiber during the drawing process. The coatings
protect the very delicate strands of glass fiber-about the size of a human hair-
and allow it to survive the rigors of manufacturing, proof testing.
cabling and installation. Today's glass optical fiber draw processes employ a
dual-layer coating approach. An inner primary coating is designed to act as an
absorber to minimize attenuation caused by micro bending. An outer
secondary coating protects the primary Coating against mechanical damage
and acts as a barrier to lateral forces. These fiber optic coating layers are
applied during the fiber draw, at speeds approaching 100 kilometers per hour
(60) mph). fiber optic coatings are applied using one of two methods: wet-on-
dry, in which the fiber passes through a primary coating application, which is
then UV cured, then through the secondary coating application which
subsequently cured; and wet-on-wet, in which the fiber passes through both
the primary and secondary coating applications and then goes to UV curing.
Fiber optic coatings are applied in concentric layers to prevent damage to the
fiber during the drawing application and to maximize fiber strength and micro
bend resistance. Under proper drawing and coating processes, the coatings are
concentric around the fiber, continuous over the length of the application and
have constant thickness.
BIBLIOGRAPHY
>www.wikipedia.org
>www.google.com
>www.arcelect.com
>www.hfcl.com
ACKNOWLEDGMENT
I wish to express my gratitude to my Physics teacher Mrs.
Ripple Mehta, who has been instrumental in helping me
complete this project.
I also wish to express my sincere thanks to our beloved
Principal Ms. Richa Agnihotri, and the management of
Sanskriti School for giving me this golden opportunity to
work on this project.
I wish to thank my parents, friends and all those who have
directly or indirectly contributed towards completion of this
project successfully and effectively.
CERTIFICATE
This is to certify that Chitra Sharma, bonafide
Student of class XII-B of Sanskriti School has successfully
completed the project titled.
“OPTICAL FIBRE”
In the laboratory of Physics prescribed by the Central
Board of Secondary Education for the year
2023-24
Date: 23/09/23
Signature:
Ms. Ripple
Mehta
By Chitra Sharma
