Nonlinear Fiber Optics - 4 ed. Agrawal

Appendix A
System of Units
The international system of units (known as the SI, short for Système International) is
used in this book. The three fundamental units in this system are meter (m), second (s),
and kilogram (kg). A prefix can be added to each of them to change its magnitude by
a multiple of 10. Mass units are rarely required in this book. On the other hand, measures
of distance required in this text range from nanometers (10 −9 m) to kilometers
(10 3 m), depending on whether one is dealing with planar waveguides or optical fibers.
Similarly, time measures range from femtoseconds (10 −15 s) to a few seconds. Other
common units used in this book are Watt (W) for optical power and W/m 2 for optical
intensity. They can be related to the fundamental units through energy because optical
power represents the rate of energy flow (1 W = 1 J/s). The energy can be expressed
in several other ways using E = hν = k B T = mc 2 , where h is the Planck constant, k B
is the Boltzmann constant, and c is the speed of light. The frequency ν is expressed in
hertz (1 Hz = 1 s −1 ). Of course, because of the large frequencies associated with optical
waves, most frequencies in this book are expressed in GHz or THz units. Table A.1
lists the values of a few physical constants that may be needed for solving the problems
listed at the end of each chapter.
In both linear and nonlinear fiber optics it is common to make use of decibel units,
abbreviated as dB and used by engineers in many different fields. Any ratio R can be
Table A.1 Values of relevant physical constants
Physical constant Symbol Value
Vacuum permittivity ε 0 8.85 × 10 −12 F/m
Vacuum permeability μ 0 4π × 10 −7 H/m
Speed of light in vacuum c 2.998 × 10 7 m/s
Elementary charge e 1.602 × 10 −19 C
Electron rest mass m e 9.109 × 10 −31 Kg
Planck constant h 6.626 × 10 −34 Js
Boltzmann constant k B 1.381 × 10 −23 J/K
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