Page 20 - Optical Communications Essentials

Basic Concepts of Communication Systems

10 Chapter One

8
about c 300,000 kilometers per second (3 10 m/s) or 180,000 miles per
5
second (1.8 10 mi/s) in a vacuum. Note that the speed of light in a material
is less than c, as described in Chap. 3.
The physical property of the radiation 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. Whereas electric signal transmission tends to use frequency to designate
the signal operating bands, optical communications generally use wavelength to
designate the spectral operating region and photon energy or optical power
when discussing topics such as signal strength or electrooptical component per-
formance. We will look at the measurement units in greater detail in Chap. 3.

1.5.2. Optical communications band
The optical spectrum ranges from about 5nm (ultraviolet) to 1mm (far infrared),
the visible region being the 400- to 700-nm band. Optical fiber communications
use the spectral band ranging from 800 to 1675nm.
The International Telecommunications Union (ITU) has designated six
spectral bands for use in intermediate-range and long-distance optical fiber
communications within the 1260- to 1675-nm region. As Chap. 4 describes,
these band designations arose from the physical characteristics of optical fibers
and the performance behavior of optical amplifiers. As shown in Fig. 1.8, the
regions are known by the letters O, E, S, C, L, and U, which are defined as
follows:
■ Original band (O-band): 1260 to 1360nm
■ Extended band (E-band): 1360 to 1460nm
■ Short band (S-band): 1460 to 1530nm
■ Conventional band (C-band): 1530 to 1565nm
■ Long band (L-band): 1565 to 1625nm
■ Ultralong band (U-band): 1625 to 1675nm

The operational performance characteristics and applications of optical fibers,
electrooptic components, and other passive optical devices for use in these
bands are described in later chapters.

Figure 1.8. Definitions of spectral bands for use in optical fiber communications.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.