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Fiber Optics Research Paper
Fiber optics is a branch of optics concerning the transmission of light by means of
optical fibers, which are thin strands of glass or other optically transparent materials.
Optical fibers can be used to guide light--which is electromagnetic radiation in a
certain frequency range--in much the same way that metal wave guides or coaxial cables
can be used to guide lower-frequency electromagnetic radiation.
Optical Fiber
An optical fiber is usually circular in cross section and consists of a core and
cladding. An optical fiber for communication applications is typically between about 0.1
and 0.2mm (0.004 and 0.008 in) in diameter. In order that the light waves be guided by
the fiber, the core must have a higher index of refraction than the cladding. One such
fiber is called a step-index fiber because the index changes abruptly at the interface
between the core and the cladding. An important variation of this structure is the
graded-index fiber, so called because the index of refraction decreases smoothly outward
from the
center with no abrupt step.
Transmission of Light
In the step-index fiber, the light wave is guided by a process called total internal
reflection. Only rays that have an angle of incidence at the core-cladding interface
greater than the critical angle will be reflected back into the core and thus guided by
the
fiber. Some rays follow a longer path through the fiber than do others. Thus a pulse of
energy entering the fiber undergoes dispersion. This effect limits the bandwidth of the
fiber and reduces the amount of information it can transmit. This undesirable feature can
be partly overcome by the use of graded-index fibers of proper design.
Applications
Fiber optics is used in several areas of telecommunications. Advantages of optical fibers
include their wide bandwidth, low attenuation, lightness, small cross section, and
non-conductivity of electricity. In telephone systems they can provide communication
channels to customers and wideband facilities for interconnecting switching offices.
Because they are non-conducting, they can be used to provide telecommunications services
to locations in electrically hostile environments, such as electric power stations. 
Because they are completely immune to induced currents from external electromagnetic
fields, optical fibers are also useful in environments where electrical noise exists,
such as hospitals and factories. Finally, their lightness makes them attractive for use
in aircraft and spacecraft as well as in portable communications systems required for
tactical military applications. All these properties make them desirable for
interconnecting computers and other sophisticated electronic equipment.
In communication-system applications, individual fibers usually are used to guide light
waves. Other applications employ bundles of fibers. One such application is the
transmission of light for illumination. Fibers used for this purpose need not have the
cladding or the index gradient of single-fiber light guides because the index step at the
glass-air interface serves to guide the light. Another application of fiber bundles is
the
transmission of images. For this application the fibers must be arranged in the bundle in
a coherent fashion. By arranging the locations of the fibers at one end (the output) of
the bundle in certain ways with respect to their location at the other end (the input),
such functions as magnification, inversion, rotation, distortion, and scrambling of the
image can be performed. Bundles of this type can be used for viewing otherwise
inaccessible areas, an example being the physician's endoscope. In order to achieve high
resolution, fibers with diameters as small as 0.02 mm (0.0008 in) are used in these
applications. Fiber bundles are also used in photography, spectroscopy, and image
processing.