Basic Principles of
Light
Light as Electromagnetic Energy
 All light is a form of electromagnetic energy.
 The electrons orbiting the atoms pick up energy from the
motion, and the energy causes them to move to higher
orbits, or energy levels.
 As they drop back to their original energy levels, they
release the energy again.
 The energy takes two forms: an electrical field and a
magnetic field.
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• The combination of these electrical and
magnetic fields is an electromagnetic
wave.
• Although the wave exists threedimensionally, it is often represented as a
two-dimensional sine wave.
• One of the most important characteristics of
electromagnetic energy is its wavelength
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• Wavelength is the distance between corresponding
points on two consecutive waves.
• Wavelength is important because it defines the
electromagnetic energy’s frequency, which
is the number of waves that pass a given point in
one second. Frequency is measured in cycles per
second, or hertz (Hz).
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• A way to express the relationship between
wavelength and frequency is that wavelength
equals the velocity of the wave (v) ) divided by
𝒗
its frequency (f), or =
𝒇
• Note that v is usually the speed of light in
vacuum or open air, approximately 300,000
km/s.
• So, it can be calculated the frequency using the
𝒗
wavelength with the equation: 𝒇 =

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• As the wavelength becomes smaller,
more waves will occur in one second,
which means that the frequency will
increase as wavelength decreases.
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• What we commonly call light is just one small
part of the electromagnetic spectrum.
• Visible light is an even smaller component, bordered
by infrared, with longer wavelengths, and
ultraviolet, with shorter wavelengths
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• The wavelengths most commonly used for fiber optics are in
the infrared range, at windows of 850 nanometers (nm),
1300 nm, and 1550 nm.
• The spectrum range of these wavelengths provides an
important combination of characteristics: it is high enough
to make high data rates possible, but low enough to
require relatively low power for transmission over long
distances.
• Between 850 nm and 1550 nm, certain regions have high
losses due to materials in the fiber, such as stray water
molecules, absorbing light at a wavelength of 1380 nm.
• The wavelengths, such as 1550 nm, are favored because
they have a low loss, allowing longer transmission distances
• Wavelengths near 1300 nm suffer less from dispersion