This document provides a 3-paragraph summary of the key concepts of fiber optics: Fiber optics uses glass or plastic fibers to guide light along its length through the process of total internal reflection. Light is transmitted from a transmitter that converts an electrical signal to light, through the fiber, and received at the other end by a receiver that converts the light back to an electrical signal. Refraction causes light to bend as it passes between materials with different refractive indices, and total internal reflection keeps light confined within the fiber when it encounters a change in index of refraction at the fiber's outer surface.

1. Fiber Optics
ECE 422L
2013

2. • Consultation Time: 2:30 – 4:30 PM
• Main Book:
• Fiber Optics Communications Technology
– by Djafar K. Mynbaev
• OPTICAL FIBER COMMUNICATION
– SUDHEESH
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3. VMG

4. UM Core Values
Excellence
Honesty and Integrity
Teamwork
Innovation

5. History
• Willebrord Snell
– a Dutch mathematician who in 1621 wrote the formula
for the principle of refraction
• Daniel Colladon and Jaques Babinet
– First demonstrated in the 1840s, The light-guiding
principle behind optical fibers
• John Tyndall (Irish inventor)
– offering public displays using water-fountains .
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6. History
• Alexander Graham Bell
– In 1880, demonstrated his photophone, one of the first
true attempts to carry complex signals with light. It was
also the first device to transmit signals wirelessly.
• William Wheeler
– in 1880, the same year that Bell’s photophone made its
debut, used pipes with a reflective coating inside that
guided light from a central arc light throughout a house.
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7. History
• Brian O’Brien,
– President of the Optical Society of America
– In 1951 suggested to use a surrounding, or
“cladding,” the fiber with a layer of material
with a lower refractive index.
• Narinder Kapany coined the term fiber
optics
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8. History
• In 1966 Charles K. Kao and George
Hockham proposed optical fibers at STC
Laboratories (STL), Harlow, when they
showed that the losses of 1000 db/km in
existing glass (compared to 5-10 db/km in
coaxial cable) was due to contaminants,
which could potentially be removed.
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9. History
• AT&T and GTE
– The first full-scale commercial application of
fiber optic communication systems occurred in
1977
– Use fiber optic telephone systems for
commercial customers.
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10. Fiber Optics
• Is a glass or plastic fiber designed to guide light
along its length by confining as much light as
possible in a propagating form.
• Are widely used in fiber-optic communication,
which permits transmission over longer distances
and at higher data rates than other forms of wired
and wireless communications.
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11. Principles of Fiber Optic Transmission
• The Fiber Optic Link
components
– Transmitter
– Receiver
– The optical fiber
– The connectors
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12. • Transmitter
– converts an electrical signal into light energy to
be carried through the fiber optic link.
– The signal could be generated by a computer, a
voice over a telephone, or data from an
industrial sensor.
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The Fiber Optic link

13. • Receiver
– Is an electronic device that collects light energy
and converts it into electrical energy, which can
then be converted into its original form.
– The receiver typically consists of a photo
detector to convert the received light into
electricity, and circuitry to amplify and process
the signal.
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The Fiber Optic link

14. • Optical Fibers
– Carry light energy from the transmitter to the
receiver. An optical fiber may be made of glass
or plastic, depending on the requirements of the
job that it will perform.
– The advantage: can carry light around corners
and over great distances.
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The Fiber Optic link

15. • Connectors
– Attached to the optical fiber
and allows it to be mated to
the transmitter or receiver to
provide solid contact.
– Must align the fiber end
precisely with the light
source or receiver to prevent
signal loss.
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The Fiber Optic link

16. Basic Principles of Light
• All light is a form of electromagnetic
energy.
• Electromagnetic energy is emitted by any
object that has a temperature above absolute
zero , which means that the atoms in the
object are in motion.
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17. • The energy takes two forms:
– an electrical field and a magnetic field, formed
at right angles to each other and at right angles
to their path of travel,
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Basic Principles of Light

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19. • Light travels at lower velocities through
various materials or media such as the
earth’s atmosphere, glass, plastic, and
water.
• A medium’s optical density, which is
different from its physical density,
determines how quickly light passes
through it.
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Basic Principles of Light

20. Refraction
• the bending of light as it
passes from one material
into another.
• occurs when light waves
change speed as they cross
the boundary between two
materials with different
optical densities.
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21. • Light slows down
at a denser medium
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Refraction

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Refraction Index

23. Refraction of Light
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24. Model used to calculate Refraction
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• Snell’s law
• n1sinθ1 = n2sinθ2

25. Critical Angle
• The incident angle required to produce
a refracted angle of 90°.
• As the incident ray moves from normal
toward the critical angle, less and less
of the incident ray’s energy is carried
into the refracted ray.
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26. Critical Angle
• Incidence angle < Critical angle
n1
n2
𝜃1
𝜃2
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27. Critical Angle
• Incidence angle =
Critical angle
• At the critical angle,
all of the incident
ray’s energy is
refracted along the
interface.
n1
n2
𝜃1
𝜃2 = 90 𝑜
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28. Critical Angle
• Incidence angle >
Critical angle
• As the incident
angle exceeds
90°, the light is
reflected
n1
n2
𝜃1 𝜃2
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29. Solving for Critical Angle
 θc = arcsin (n2 ÷ n1)
• So if we want to know the critical angle of
an optical fiber having a core RI of n1 = 1.51
and a cladding RI of n2 = 1.46:
 θc = arcsin(1.46 ÷ 1.51) = 75.211°
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30. Total Internal Reflection
• Occurs when
Incidence angle >
critical angle
• All light reflects back
toward the incident
medium
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Total Internal Reflection
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32. Sample Problem
• Calculate the critical angle of an optical
fiber with a core RI of 1.48 and a
cladding RI of 1.46.
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33. Fresnel Reflections
• Reflected at an angle equal to the angle of
incidence.
• The greater the difference in RI between the
two materials, the more light will be
reflected.
• You experience Fresnel reflection whenever
you look through a window and see a faint
reflection of yourself in the glass.
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34. • Augustin Fresnel determined how to
calculate the amount of light lost through
Fresnel reflection
• equation: ρ = ((n1 – n2) ÷ (n1 + n2))2
– where ρ is the amount of light reflected and n is
the RI of the medium.
• To calculate the loss in decibels
– dB = 10Log10 (1 – ρ)
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Fresnel Reflections

35. Sample
• Calculate the dB loss due to Fresnel
reflection of a light from the air entering
a fiber core with an RI of 1.48.
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36. Reference
• Fiber Optics Communications Technology
– by Djafar K. Mynbaev
• OPTICAL FIBER COMMUNICATION
– SUDHEESH
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