Electronics and Electrical Communications
Department
Optical Communications
Dr. Nermeen Mohamed
Lecturer at Electronics and Electrical
Communications Department, Tanta University
Lecture 1
Written Exam
Mark Distribution
Oral/Practical Exams
(125 degrees) Team Work
Course Rules
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What is meant by Optical
Communications ?
• An optical fiber is a thin, flexible, transparent cable that uses light quickly and efficiently to transmit
data
• Light is used to communicate between optical fibers and not electricity, and through the use of light,
communication speeds increase
It operates on the total internal reflection principle
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Basic Principle of Fiber
Light basics
light deviates from its original path while travelling from one medium to another
FREQUENCY : It is the number
of pulse per second emitted from
a light source.
In terms of optical pulse :
1Hz = 1 pulse/ sec.
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Light spectrum
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Ray Optics If θ2 = 90° then θ1 = θcritical
Refraction of light
Light changes direction; this phenomenon
is called refraction of light
Refractive index n = c / ν
Snell’s law 𝐧𝟏 𝐬𝐢𝐧 𝛉𝟏 = 𝐧𝟐 𝐬𝐢𝐧 𝛉𝟐
• In a homogeneous medium, light
Reflection of light rays are straight lines
• Light may be absorbed or reflected
If the surface upon which the light beam falls is perfectly black, there is no reflection;
that is, the light is totally absorbed.
• Reflected ray lies in the plane of incidence and angle of incidence will be
equal to the angle of reflection
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Types of reflection :
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Acceptance angle 𝛉𝐚 : is the arcsine of numerical aperture NA
Numerical aperture is the ability of the optical system to collect the entire light incident
on it, in one area.
𝑵𝑨 = 𝒏 𝒄𝒐𝒓𝒆 𝟐 − 𝒏 𝒄𝒍𝒂𝒅𝒅𝒊𝒏𝒈 𝟐
Can be defined as the external maximum angle at
which the light entering the core is transmitted
through the fiber and propagated without being
refracted.
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The main principle for optical communication :
Total internal reflection requirements :
• Light wave should be propagated from denser medium to rarer
• If incident angle is larger than critical angle of core−cladding interface then light ray is reflected back in
same medium
Light rays incident on the core-cladding interface at an angle greater than the critical angle are
trapped inside the core of the fiber
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Fiber Optic Cable : The core of a fiber cable is a cylinder of plastic
that runs all along the fiber cable’s length.
Cladding is an outer optical material that protects
the core. The main function of the cladding is that it
reflects the light back into the core. When light
enters through the core (dense material) into the
cladding(less dense material), it changes its angle,
and then reflects back to the core.
Cross sectional view of a fiber
A glass fiber consists of a cylindrical central core cladded by a
material of slightly lower refractive index.
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Advantages of Optical Communication System
Size and weight
Security
Speed and distance
Electromagnetic interference
Bandwidth
Signal loss
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Examples of Optical Communication System
Telephone
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• The internet signal is transmitted via fiber optic cables to the fiber optic modems.
Internet • The modem transforms the internet signals into electronic data.
• This transmission is a full-duplex transmission. That means the data can be
transmitted from the internet source to the electronic device and vice versa.
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Military
Submarine missions
Communication missions
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Eye diagnosis
Medical uses
Robotics surgery using optical fiber shape sensing
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Demerits of Optical Communication System
Cost over short distances
Installation
Additional nodes
Testing
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Next lecture Agenda :
• Index modes for optical fiber cables
• Comparison between different cables
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