Discussion on Fiber Optic Communication System

1. FIBER OPTIC
COMMUNICATIO
N SYSTEMS
Transmission Media and Antenna
Systems – Lecture 2

2. Lesson Objectives
After completing this lecture, you should be able to:
• Define what is a fiber optic communication system
• Enumerate the advantages and disadvantages of using a fiber optic communication system
• Discuss the brief history of fiber optics
• Understand the various theories of light
• Discuss the different properties of light
• Solve problems involving reflection and refraction
• Define and discuss fiber optic cables
• Understand the concept of total internal reflection
• Define the various optical fiber parameters such a critical angle and numerical aperture
• Understand the concept of modes in optical fibers
• Define what is an index profile
• Understand the different losses in fiber optic cables
• Discuss about splices, optical transmitters and optical receivers

3. Fiber Optic
Communication
System
• It is a communication system
wherein an electrical signal is
converted to optical signal, then
send the optical signal over an
optical fiber and then convert the
optical signal back to an
electrical signal.

4. Fiber Optic Communication Systems
ADVANTAGES DISADVANTAGES
 Greater information capacity  Interfacing costs
 Immunity to crosstalk  Strength
 Immunity to static interference  Remote electrical power
 Environmental immunity  Specialized tools, equipment and training
 Safety
 Security
 Economics

5. History of Fiber
Optics
 BELL experimented the transmission of
sound waves over a beam of light called a
PHOTOPHONE

6. History of
Fiber Optics
• By 1950s, Heel, Hopkins and
Kapany experimented with light
transmission through bundles of
fibers .
• This led to the development of
the flexible fiberscope.

7. History of Fiber Optics
• Dr. Narinder Singh Kapany is widely acknowledged as
the father of optical fiber
• He coined the term fiber optics in 1956

8. History of Fiber
Optics
• Theodore Maiman invented the first LASER
in late 1950s

9. History of
Fiber Optics
• Charles Kao and George
Hockham added cladding to the
fiber optic communications
medium

10. Theories of Light
The Corpuscular Theory
Proposed by Sir Isaac Newton, this states
that light emitted by luminous objects
consists of tiny particles of matter called
corpuscles. When corpuscles hit a surface,
each particle is reflected.

11. Theories of
Light
• The Wave Theory
• Proposed by Christian Huygens,
a Dutch scientist. This states that
light is emitted in a series of
waves that spread out from a light
source in all directions. These
waves are not affected by gravity.

12. Theories of
Light
The Electromagnetic Theory
• Proposed by James Maxwell,
this states that light waves do not
require a medium for
transmission. Light waves
posses electrical and magnetic
properties and can travel through
a medium.

13. Theories of Light
• The Quantum Theory
• Proposed by Max Planck, German scientist in
1900. This states that light waves travel as
separate packets of energy called quanta or
photon.

14. Optical Spectrum

15. Optical Spectrum
Photon Energy
The energy of a photon is given by the Planck-
Einstein relation:
𝐸 = ℎ𝑓 =
ℎ𝑐
𝜆
• Problem Solving
Find the energy in electron volts, of one photon
at a wavelength of 1𝜇𝑚.

16. Reflection and Refraction
• Reflection
This occurs when a wave strikes an object and
bounces back (toward the source)
• Refraction
When a light wave passes from one medium into
a medium having a different velocity of
propagation (the speed waves can travel through
a medium), a change in the direction of wave will
occur.

17. Reflection and Refraction

18. Problem Solving
• The speed of light in material A is 2.00 𝑥 108
𝑚/𝑠. Determine the refractive index of the material .

19. Problem Solving
• Light travels form air into optical fiber with an index of refraction of 1.44. If the angle of incidence on
the end of the fiber is 22°, what is the angle of refraction inside the fiber?

20. Optical
Fiber

21. Optical Fiber
• Core
Refers to a part of an optical fiber where light travels
• Cladding
Refers to the part of the optical fiber that reduces loss of light from the core into the surrounding air,
reduces scattering loss at the surface of the core, protects the fiber from absorbing surface
contaminants and adds mechanical strength to the fiber
• Buffer
Refers to the part of an optical fiber that serves as a protection from physical damage and prevents
scattering losses due to microbends.

22. How does
light travel?
Total Internal Reflection

23. Total Internal Reflection
Light propagates down the length of the fiber through the principle of total internal reflection.
Total internal reflection occurs when the angle of incidence is large enough to force the refracted ray
to bend 90° with respect to the incident ray.
Conditions:
1. Core index must be greater than the cladding index
2. Light must approach the wall with an angle of incidence greater that the critical angle

24. Critical Angle
The minimum angle of incidence at which light
ray may strike the interface of two media and
result in an angle of refraction of 90 degrees.

25. Problem Solving
• A fiber has an index of refraction of 1.6 for the core and 1.4 for the cladding. Calculate the critical
angle.

26. Problem Solving
• A fiber has an index of refraction of 1.6 for the core and 1.4 for the cladding. Calculate the angle of
refraction for angle of incidence of 70 degrees.

27. Numerical
Aperture
It is the FIGURE OF MERIT commonly used to
measure the magnitude of the acceptance
angle. This is described as the light gathering
ability of an optical fiber.

28. Problem Solving
• An optical fiber is made of glass with a surface index of 1.55 and is clad with another glass with a
refractive index is 1.51 Launching takes place on air. Determine the numerical aperture and the
acceptance angle of the fiber.