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HISTORY OF FIBER OPTIC TECHNOLOGY
People have used light to transmit information for hundreds of years. However, it was
not until the 1960s, with the invention of the laser, that widespread interest in optical
(light) systems for data communications began. The invention of the laser prompted
researchers to study the potential of fiber optics for data communications, sensing, and
other applications. Laser systems could send a much larger amount of data than telephone,
microwave, and other electrical systems. The first experiment with the laser involved
letting the laser beam transmit freely through the air. Researchers also conducted
experiments letting the laser beam transmit through different types of
waveguides. Glass
fibers, gas-filled pipes, and tubes with focusing lenses are examples of optical
waveguides. Glass fibers soon became the preferred medium for fiber optic research.
Initially, the very large losses in the optical fibers prevented coaxial cables from
being replaced. Loss is the decrease in the amount of light reaching the end of the
fiber. Early fibers had losses around 1,000 dB/km making them impractical for
communications use. In 1969, several scientists concluded that impurities in the fiber
material caused the signal loss in optical fibers. The basic fiber material did not
prevent the light signal from reaching the end of the fiber. These researchers believed it
was possible to reduce the losses in optical fibers by removing the impurities. By
removing the impurities, construction of low-loss optical fibers was possible.
There are two basic types of optical fibers, multimode fibers and single mode fibers.
Chapter 2 discusses the differences between the fiber types.
In 1970, Corning Glass Works made a multimode fiber with losses under 20 dB/km.
This same company, in 1972, made a high silica-core multimode optical fiber with 4dB/km
minimum attenuation (loss). Currently, multimode fibers can have losses as low as 0.5
dB/km at wavelengths around 1300 nm. Single mode fibers are available with losses lower
than 0.25 dB/km at wavelengths around 1500 nm.
Developments in semiconductor technology, which provided the necessary light sources
and detectors, furthered the development of fiber optics. Conventional light sources, such
as lamps or lasers, were not easily used in fiber optic systems. These light sources
tended to be too large and required lens systems to launch light into the fiber. In 1971,
Bell Laboratories developed a small area light-emitting diode (LED). This light source was
suitable for low-loss coupling to optical fibers. Researchers could then perform
source-to-fiber jointing easily and repeatedly. Early semiconductor sources had operating
lifetimes of only a few hours. However, by 1973, projected lifetimes of lasers advanced
from a few hours to greater than 1,000 hours. By 1977, projected lifetimes of lasers
advanced to greater than 7,000 hours. By 1979, these devices were available with projected
lifetimes of more than 100,000 hours.
In addition, researchers also continued to develop new fiber optic parts. The types of
new parts developed included low-loss fibers and fiber cables, splices, and connectors.
These parts permitted demonstration and research on complete fiber optic systems.
Advances in fiber optics have permitted the introduction of fiber optics into present
applications. These applications are mostly in the telephone long-haul systems, but are
growing to include cable television, computer networks, video systems, and data links.
Research should increase system performance and provide solutions to existing problems in
conventional applications. The impressive results from early research show there are many
advantages offered by fiber optic systems.
Q.6 Define loss.
Q.7 In 1969, what did several scientists conclude about optical fiber loss?
Q.8 How can loss be reduced during construction (or fabrication) of optical fibers?
Q.9 What are the two basic types of optical fibers?
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