LESSON
12
FIBER OPTICS
I.
Consider the
following questions
in the
group of
four.
A spokesperson will report on your discussion
to the whole group.
1. Do you know
what fiber optics deals with?
2. What distance can fiber-optic systems cover?
3. Do you know
when optical fibers first came into use?
II.
Read the text
below and check its
comprehension.
Fiber optics is a branch of optics dealing with the
transmission of light
through fibers or
thin rods of glass or some other transparent material
of high refractive index. If
light is admitted at one
end
of a fiber, it can travel through the fiber with
a very low loss, even if the fiber is curved.
The principle on which
this transmission of
light depends is that of total in-ternal
reflection. Light traveling
inside the fiber center, or core, strikes the out-side
surface at an angle of incidence greater than
the critical angle, so that all the light is reflected
toward the inside of
the fiber without loss. Thus light can be transmitted over long distances by
being reflected inward thousands of times. In order to avoid losses through
the scattering of light by
impurities on the sur-face of the fiber,
the optical fiber core is clad with a
glass layer of much lower refractive
index;
the reflections occur at the interface of the glass fiber and
the cladding.
The simplest application of
optical fibers is the
transmission of light to loca-tions
otherwise hard to reach,
е.g., the bore of a dentist's drill. Also, bundles
of several thousand very thin fibers assembled precisely side by side and optical-ly
polished at their ends, can be used to
transmit images. Each
point
of the ima-ge projected on one face of the bundle is reproduced at
the other end of the bundle, reconstituting the
image,
which can be observed through a
magnifier. Image transmission by
optical fibers is widely used in medical
instruments for viewing inside the
human body and for laser surgery, in facsimile systems, in phototypesetting,
in computer graphics, and in many
other applications.
Optical fibers are
also being used in a wide variety of sensing devices, ran-ging
from thermometers to gyroscopes. The potential of their applications in this field is nearly unlimited,
because the light sent through them
is sensitive to many environmental changes,
including pressure, sound waves, and
strain, as well as heat and motion. The fibers
can be especially useful where electri-cal effects
could make ordinary wiring useless,
less
accurate, or even hazard-ous. Fibers have
also
been
developed
to carry high-power laser beams for
cut-ting
and drilling.
One growing application of optical fibers is in communication. Because
the information-carrying capacity of
a signal increases with frequency, the use of
laser light offers many advantages. Fiber-optic
laser systems are being used in
communications networks. Many
long-haul fiber communications networks
for both transcontinental
connections and, through
undersea cables,
internati-onal connections are
in operation. One advantage of optical fiber systems is the
long distances that can be maintained
before signal repeaters are needed to
regenerate signals. These are
currently separated by about 100 km
(about
Local area networks are another growing application for fiber optics. Unlike long-haul communications, these
systems connect many local subscribers to expensive centralized equipment such as computers and printers. This system expands the utilization of
equipment and can easily accommodate
new users on a network. Development of new electro-optic and integrated-optic
compo-nents will further expand
the capability of fiber
systems.
Comprehension
Check
Up
1. What is fiber optics?
2.
What is the principle of light transmission? 3. How can we avoid losses during
transmission? 4. Where do the
reflections occur? 5. How can one transmit images using optical
fibers? 6. Where is image transmission used? 7. Why do applications of sensing devices are almost
unlimited? 8. Why are optical fibers widely used in communication? 9. How can subscribers get the benefit from
systems with optical fibers?
10. What will further expand the
capability of fiber systems?
III.
Choose the best answer.
1. Fiber
optics refers to…
a) a number of threads used to make ropes; b)
scientific study of light; c) the process of using thin threads of glass to
carry information; d) the burning material
2. The word reflection
means…
a) a perfect example of smth.; b) an image
reflected in a mirror or similar surface; c) permission; d) natural ability to
react quickly
3. The best explanation of the word subscriber
might be…
a) a person who does part of the work of another
person; b) a thief; c) an instrument for cutting wood, metal; d) someone who
gives money for a ser-vice
4. The verb to project
means …
a) to make a picture on a film, photo, etc.; b)
to design; c) to make progress; d) to prohibit
5. The word variety
implies…
a) the amount of money that smth. is worth; b)
an action; c) velocity; d) a lot of things that are different from each other
6. The best explanation of the word long-haul might be…
a) something that lasts for a long time; b)
long hair; c)something that goes very long distance; d) deep hole
7. The word currently
means…
a) long time ago; b) at present; c) soon; d)
quickly
8. The word transparent
refers to…
a) something that allows light to pass through
it; b) transport; c) smth. that moves quickly; d) people who haven’t got their
own children and raise abandoned children
9. The word application
refers to …
a) the process of fixing smth. to smth.; b)
solution; c) practical purpose for which a machine, an idea can be used; d)
escape.
10. The verb to extend means…
a) to show smth.; b) to explain smth.; c) to
expect smth. to happen; d) to make smth. bigger or longer.
11. The word angle deals with…
a) a spirit who lives with God in heaven; b) a
close relative; c) the space between two straight crossed lines, d) an
Englishman.
12. The word sensitive means…
a) Changeable; b) able to react to very small
changes of heat, light; c) sincere; d) simultaneous.
IV.
Use the
right verb from those given
below.
to expand, to
transmit, to accommodate, to occur, to observe, to strike, to reconstitute, to
regenerate, to reflect, to separate, to clothe (clad).
1. To … the reconstituted image we
should use a magnifier. 2. In order to avoid losses we should … the core of the
fiber with glass layer. 3. Projection of the image on the bundle … the
same image at the other end of the
bundle. 4. The capabilities of fiber systems will be … with the designing of
various optic components. 5. The outside surface is … by light traveling inside
the fiber. 6. The long distances are … for electrical systems. 7. Fiber bundles
are used to … image. 8. Signal repeaters are used to … signals. 9. Local area
networks … new uses on a network. 9. Light mailing along the core is … toward
the inside of the fiber. 10 The reflections … at the interface of the optical
fiber and glass layer of much lower refractive index.
V.
Are the following statements True or False?
1. Fiber optics deals with the transmission of
light through opaque materi-als. 2. The fibers are used where electrical
effects could make ordinary wiring useless and less accurate. 3. In order to
avoid losses the optical fiber core is cleaned from a glass layer.
4. The
fibers are absolutely useless where electri-cal effects could make ordinary wiring useful and more accurate. 5. Long-haul
fiber communication networks are used for international and transcontinental connections.
VI.
Divide the text
into paragraphs.
VII.
Express the main
idea of each paragraph in one sentence.
VIII.
Summarize the text and be ready to retell it.
IX. Speak on pros and cons of fiber optics if any.