4
1 Perspectives on Lightwave Communications
availability and continuous expansion of the Internet, and an extensive choice of
remotely accessible application programs and information databases, resulted in a
dramatic rise in PC and mobile device usage. To handle the ever-increasing demand
for high-bandwidth services in locations ranging from homes and mobile devices to
large businesses and research organizations, telecom companies worldwide greatly
enhanced the capacity of fiber lines. This was accomplished by adding more independent signal-carrying wavelengths on individual fibers, increasing the transmission
speed of information being carried by each wavelength, and utilizing more advanced
signal modulation techniques with improved spectral efficiency.
1.1.2 Benefits of Using Optical Fibers
The advantages of optical fibers compared to copper wires include the following:
Long Distance Transmission Optical fibers have lower transmission losses compared
to copper wires. Consequently data can be sent over longer distances, thereby
reducing the number of intermediate repeaters needed to boost and restore signals
in long transmission spans. This reduction in equipment and components decreases
system cost and complexity.
Large Information Capacity Optical fibers have wider bandwidths than copper
wires, so that more information can be sent over a single physical line. This property decreases the number of physical lines needed for sending a given amount of
information.
Small Size and Low Weight The low weight and the small dimensions of fibers
offer a distinct advantage over heavy, bulky wire cables in crowded underground city
ducts or in ceiling-mounted cable trays. This feature also is of importance in aircraft,
satellites, and ships where small, low-weight cables are advantageous.
Immunity to Electrical Interference An especially important feature of an optical
fiber relates to the fact that it is a dielectric material, which means it does not conduct
electricity. This makes optical fibers immune to the electromagnetic interference
effects seen in copper wires, such as inductive pickup from other adjacent signalcarrying wires or coupling of electrical noise into the line from any type of nearby
electronic equipment.
Enhanced Safety Optical fibers offer a high degree of operational safety because
they do not have the problems of ground loops, sparks, and potentially high voltages
inherent in copper lines. However, precautions with respect to possible high-intensity
laser light emissions need to be observed to prevent eye damage.
Increased Signal Security An optical fiber offers a high degree of data security
because the optical signal is well confined within the fiber and an opaque coating
around the fiber absorbs any light signal emissions. This feature is in contrast to
copper wires where electrical signals potentially could be tapped off easily. Thus
1 Perspectives on Lightwave Communications
availability and continuous expansion of the Internet, and an extensive choice of
remotely accessible application programs and information databases, resulted in a
dramatic rise in PC and mobile device usage. To handle the ever-increasing demand
for high-bandwidth services in locations ranging from homes and mobile devices to
large businesses and research organizations, telecom companies worldwide greatly
enhanced the capacity of fiber lines. This was accomplished by adding more independent signal-carrying wavelengths on individual fibers, increasing the transmission
speed of information being carried by each wavelength, and utilizing more advanced
signal modulation techniques with improved spectral efficiency.
1.1.2 Benefits of Using Optical Fibers
The advantages of optical fibers compared to copper wires include the following:
Long Distance Transmission Optical fibers have lower transmission losses compared
to copper wires. Consequently data can be sent over longer distances, thereby
reducing the number of intermediate repeaters needed to boost and restore signals
in long transmission spans. This reduction in equipment and components decreases
system cost and complexity.
Large Information Capacity Optical fibers have wider bandwidths than copper
wires, so that more information can be sent over a single physical line. This property decreases the number of physical lines needed for sending a given amount of
information.
Small Size and Low Weight The low weight and the small dimensions of fibers
offer a distinct advantage over heavy, bulky wire cables in crowded underground city
ducts or in ceiling-mounted cable trays. This feature also is of importance in aircraft,
satellites, and ships where small, low-weight cables are advantageous.
Immunity to Electrical Interference An especially important feature of an optical
fiber relates to the fact that it is a dielectric material, which means it does not conduct
electricity. This makes optical fibers immune to the electromagnetic interference
effects seen in copper wires, such as inductive pickup from other adjacent signalcarrying wires or coupling of electrical noise into the line from any type of nearby
electronic equipment.
Enhanced Safety Optical fibers offer a high degree of operational safety because
they do not have the problems of ground loops, sparks, and potentially high voltages
inherent in copper lines. However, precautions with respect to possible high-intensity
laser light emissions need to be observed to prevent eye damage.
Increased Signal Security An optical fiber offers a high degree of data security
because the optical signal is well confined within the fiber and an opaque coating
around the fiber absorbs any light signal emissions. This feature is in contrast to
copper wires where electrical signals potentially could be tapped off easily. Thus