lecture slides on fiber optics

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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31. 31
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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