1.1 Reasons for Fiber Optic Communications
5
optical fibers are attractive in applications where information security is important,
such as financial, legal, government, and military systems.
1.2 Optical Wavelength Bands
1.2.1 Electromagnetic Energy Spectrum
All communication systems use some form of electromagnetic energy to transmit
signals. The spectrum of electromagnetic (EM) radiation is shown in Fig. 1.2. Electromagnetic energy is a combination of electrical and magnetic fields and includes
power, radio waves, microwaves, infrared light, visible light, ultraviolet light, X rays,
and gamma rays. Each discipline takes up a portion (or band) of the electromagnetic
spectrum. The fundamental nature of all radiation within this spectrum is that it can
be viewed as electromagnetic waves that travel at the speed of light, which is about c
= 3 × 10
8 m/s in a vacuum. Note that the speed of light s in a material is smaller by
the refractive-index factor n than the speed c in a vacuum, as described in Chap. 2.
For example, n ≈ 1.45 for silica glass, so that the speed of light in this material is
about s = c/n = 2 × 10
8 m/s.
The physical properties of the waves in different parts of the spectrum can be
measured in several interrelated ways. These are the length of one period of the
wave, the energy contained in the wave, or the oscillating frequency of the wave.
10 -2
10 10
10 8
10 6
10 18
10 16
10 14
10 12
10 3
Frequency (Hz)
Photon energy (eV)
Wavelength (m)
Radio
Microwaves
X rays
Infrared
Fiber optics
0.8 - 1.6 µm
Ultraviolet
Visible light
10 -4
10 -8
10 -6
10 -3
10 -5
0.1
10
1
1000
Fig. 1.2 The spectrum of electromagnetic radiation
5
optical fibers are attractive in applications where information security is important,
such as financial, legal, government, and military systems.
1.2 Optical Wavelength Bands
1.2.1 Electromagnetic Energy Spectrum
All communication systems use some form of electromagnetic energy to transmit
signals. The spectrum of electromagnetic (EM) radiation is shown in Fig. 1.2. Electromagnetic energy is a combination of electrical and magnetic fields and includes
power, radio waves, microwaves, infrared light, visible light, ultraviolet light, X rays,
and gamma rays. Each discipline takes up a portion (or band) of the electromagnetic
spectrum. The fundamental nature of all radiation within this spectrum is that it can
be viewed as electromagnetic waves that travel at the speed of light, which is about c
= 3 × 10
8 m/s in a vacuum. Note that the speed of light s in a material is smaller by
the refractive-index factor n than the speed c in a vacuum, as described in Chap. 2.
For example, n ≈ 1.45 for silica glass, so that the speed of light in this material is
about s = c/n = 2 × 10
8 m/s.
The physical properties of the waves in different parts of the spectrum can be
measured in several interrelated ways. These are the length of one period of the
wave, the energy contained in the wave, or the oscillating frequency of the wave.
10 -2
10 10
10 8
10 6
10 18
10 16
10 14
10 12
10 3
Frequency (Hz)
Photon energy (eV)
Wavelength (m)
Radio
Microwaves
X rays
Infrared
Fiber optics
0.8 - 1.6 µm
Ultraviolet
Visible light
10 -4
10 -8
10 -6
10 -3
10 -5
0.1
10
1
1000
Fig. 1.2 The spectrum of electromagnetic radiation