26
1 Perspectives on Lightwave Communications
The following chapters of this book present the fundamental principles for understanding and applying a wide range of optical fiber technologies to modern communication networks. The sequence of topics moves systematically from the underlying
principles of components and their interactions with other devices in an optical fiber
link, through descriptions of the architectures and performance characteristics of
complex optical links and networks, to essential measurement and test procedures
required during network installation and maintenance. By mastering these fundamental topics the reader will be prepared not only to contribute to disciplines such
as current device, communication link, or equipment designs, but also to understand
quickly any further technology developments for future enhanced networks.
Problems
1.1 What are the energies in electron volts (eV) of photons at wavelengths 850,
1310, 1490, and 1550 nm?
1.2 A fundamental analog signal is the sine wave shown in Fig. 1.13. Its three main
features are its amplitude, period or frequency, and phase. The amplitude is the
waveform magnitude, which is measured in volts, amperes, or watts depending
on the signal type. The frequency f is the number of cycles or oscillations per
second and is expressed in units of hertz (Hz). The period T is the inverse of
the frequency, that is, T = 1/f. The parameter phase describes the position of
the waveform relative to time zero and is measured in degrees or radians (rad)
with 180° = π rad. Consider three sine waves have the following periods:
25 ms, 250 ns, 125 ps. What are their frequencies?
1.3 If the crests and troughs of two sine waves that have the same period occur at
the same time, they are in phase. Otherwise they are said to be out of phase.
Consider two waves that have amplitudes A 1 (t) and A 2 (t), respectively, at a
time t. The amplitude of the resulting wave then is A(t) = A 1 (t) + A 2 (t). (a)
If two in-phase waves have the same maximum amplitude A and the same
period, what is the maximum amplitude of the combined wave? This case is
called constructive interference. (b) What is the maximum amplitude of the
combined wave if the two waves are 180° (π rad) out of phase? This case is
called destructive interference.
Fig. 1.13 A fundamental sine wave analog signal showing the amplitude, period or frequency, and
phase
1 Perspectives on Lightwave Communications
The following chapters of this book present the fundamental principles for understanding and applying a wide range of optical fiber technologies to modern communication networks. The sequence of topics moves systematically from the underlying
principles of components and their interactions with other devices in an optical fiber
link, through descriptions of the architectures and performance characteristics of
complex optical links and networks, to essential measurement and test procedures
required during network installation and maintenance. By mastering these fundamental topics the reader will be prepared not only to contribute to disciplines such
as current device, communication link, or equipment designs, but also to understand
quickly any further technology developments for future enhanced networks.
Problems
1.1 What are the energies in electron volts (eV) of photons at wavelengths 850,
1310, 1490, and 1550 nm?
1.2 A fundamental analog signal is the sine wave shown in Fig. 1.13. Its three main
features are its amplitude, period or frequency, and phase. The amplitude is the
waveform magnitude, which is measured in volts, amperes, or watts depending
on the signal type. The frequency f is the number of cycles or oscillations per
second and is expressed in units of hertz (Hz). The period T is the inverse of
the frequency, that is, T = 1/f. The parameter phase describes the position of
the waveform relative to time zero and is measured in degrees or radians (rad)
with 180° = π rad. Consider three sine waves have the following periods:
25 ms, 250 ns, 125 ps. What are their frequencies?
1.3 If the crests and troughs of two sine waves that have the same period occur at
the same time, they are in phase. Otherwise they are said to be out of phase.
Consider two waves that have amplitudes A 1 (t) and A 2 (t), respectively, at a
time t. The amplitude of the resulting wave then is A(t) = A 1 (t) + A 2 (t). (a)
If two in-phase waves have the same maximum amplitude A and the same
period, what is the maximum amplitude of the combined wave? This case is
called constructive interference. (b) What is the maximum amplitude of the
combined wave if the two waves are 180° (π rad) out of phase? This case is
called destructive interference.
Fig. 1.13 A fundamental sine wave analog signal showing the amplitude, period or frequency, and
phase