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JEFF & RICH
4th HOUR PHYSICS
Goals and Objectives
The goal of this
page is to give a basic overview of fiber optics - their physics, fabrication,
and applications.
The objective is
to have individuals be able to complete the quiz at the end successfully.
Bibliography
K. Lee
Lerner and Brenda Wilmoth Lerner. “Fiber Optics.” The
Gale Encyclopedia of Science.
“ How Fiber Optics Work.” How Stuff Works. December 2005. Howstuffworks.com.
<http://electronics.howstuffworks.com/fiber-optic.htm/
“A Brief History of Fiber Optic Technology” Fiber Optics. December 2005. Force, Incorporated.
<http://www.fiber-optics.info/fiber-history.htm
Gardner,
Robert. Optics. Twenty-first Centruy Books.
1994.
“Fiber
Optics.” The New Book of Popular Science. 2002
Physics Behind Them
What is
fiber optics?
Optical fibers are made from a very thin strand of glass or
plastic, and are able to transfer light signals from a starting point to a
destination. Optical cables can also be
referred to as optical waveguides, because of the way they transmit light.
Each optical wire is made up of the light carrying core, encased
in a cladding (protective coating) and then enclosed in an outer jacket for
more protection. There are three types
of cables: glass core/ glass cladding; glass core/ plastic cladding; or plastic
core/plastic cladding. Please see figure 1.1.
Figure 1.1
©howstuffworks.com
What makes
them work?
©howstuffworks.com
Fiber optics work on the physics’ law of total internal
reflection. Snell’s law of refraction
and reflection states that light will be bent from its original path to a
larger angle in the second material (cladding). As the incoming (incident)
angle increases so does the refracted angle. The incoming angle can be
increased to the point that the ray is refracted (critical angle) at 90 degrees
and never escapes. However the Second Law of Thermodynamics states that light
cannot travel indefinitely; light will be absorbed by impurities in the glass,
or escape.
So basically most of the light stays in the fiber as the light
makes its way down the cable, but it is possible some might escape.
Light
travels down the cable by bouncing back and forth down the tube.
© howstuffworks.com
Improvements to Fiber Optics
©Corning Cable System
Fiber optics are definitely an
improvement to older technology.
Before, we were limited by light leaking through the glass, however the
cables have a much better seal now.
Also, the bundles are protected by a plastic covering. The glass that is
used in fiber optics has been improved significantly since the 1970’s. With the best glass available today, you
could create a window pane 1 mile thick, and it would still have less
distortion than a regular window in a house.
Another example of the technological advantage can be seen in the
picture above. The optical fiber cable
in the foreground has the equivalent information-carrying capacity of the
copper cable in the background.
The military started using fiber optics during
the 1970’s by installing fiber optic phones in their ships. Since they were so successful, the military
has continued to update and upgrade their machines with fiber optics. Phone companies also competitively lay down
thousands of miles of fiber optic cable in order to be the best service provider. Fiber optics will only increase in popularity
in the coming years, approximately half a billion people regularly access the
internet, and 40 million other people access it moderately. Since fiber optics has increased the
popularity of the internet; the internet has gr,wn to
contain over 2 billion websites.
Application
www.seton.co.uk/images/productsTST106-200.jpg
A fiberscope is a specific optical
fiber device in which thousands of fiber optic wires are combined in order to
transmit an image. The image is carried
through one end of the wire, through 750,000 separate cables all about .001 cm
in diameter or approximately 10 microns across. The smallest wires are 5 microns
across. The pictures for fiberscope are
formed by the thousands of fibers combining a small part of the image they
see. Obviously, the fibers must be
relative in the eyepiece, as they are on the lens, otherwise you will get a
jumbled image.
Fiberscopes are applied in many and
a variety of careers. One field that
uses fiberscopes extensively is medicine.
A Gastroscope is used specifically for seeing the inside of the
stomach. By using this device doctors
can tell if a patient has a blockage in the stomach or any other ailment. There are also other less specific scopes
which allow doctors to see other parts of the body such as: the bladder, the uterus,
and the colon. With this technology it
allows doctors to do less invasive surgeries, which leaves patients with less
scarring, and shorter recovery times.
Fiberscopes are also used in
industry. They can inspect operations
because of there flexibility, otherwise it would be inaccessible by any other
means. Some examples would be turbine
blades, boiler tubes, plumbing, and various parts of nuclear reactors. Fiberscopes have
also been used as stress sensors in planes, bridges, and other architectural
structures. Some regular buyers of fiberscopes are the Army, the Navy, Boeing,
and GE.
Since fiberscopes can be used for a
variety of projects, there are many businesses that rent or sell fiberscopes to
people. There is also a variety of
classes that you can take on fiberscopes, from maintenance to becoming
certified to use them for a lab or business.
The picture to the right is from
The black rod is a human hair. The glowing
strand is a fiber optic wire. This shows
the latest in fiber optic technology.
http://www.olympussurgical.com/images/content/applications/Vascular%20Surgery/vascular.jpg
Image provided by NASA. A
turbine is inspected with fiber optics to make sure there is no malfunction.
For more
information about fiber optics click on the link http://electronics.howstuffworks.com/fiber-optic.htm
It goes to howstuffworks.com.
Ready to Test Your New
Knowledge!?
Quiz:
Take this quiz to see if you
have learned anything from this site.
The answers are farther down the page.
1.) What is the specific name
of the fiberscope used for viewing the stomach?
2.) What decade did fiber
optics start becoming popular for communications?
3.) What is another name for
fiber optics?
4.) How thick is the thinnest
fiber optic wire?
5.) What is the innermost
part of a fiber optic wire?
6.) Which physics law does
fiber optics work on?
7.) How does light travel
down a fiber optics cable?
8.) Name two different fields
in which fiber optics are used regularly and were mentioned on this site.
9.) True or false, fiber
optics are becoming so widely used that many businesses rent or sell them to
people.
10.) What law states that
light can not travel indefinitely?
Answers
1) Gastroscope
2) 1970’s
3) Optical Waveguides
4) 5 microns in diameter
5) The core
6) The law of internal
reflection
7) By bouncing back and forth
down the fiber optics wire.
8) Health/Medicine and
Industry
9) True
10) Second law of
Thermodynamics
How many did you get right?
1-2 You need to read more carefully
3-4 Try Again
5-6 Better
7-8 Science Buff
9-10 Congratulations! You’re a Physics Guru!