Elenco Fiber Optics Voice Data Kit - Manual (Page 13)

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Flexible as Copper Wire — And Stronger
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In the previous experiment you saw how easy it was to scratch the fiber's cladding. When that
occurred, light was free to escape. In the commercial world, a fiber's optical cladding is protected from
damage by adding another outer layer called the jacket. The fiber you will use in this experiment has a
.6 mm (.024 inches) thick black polyethylene jacket covering a 980
µm diameter combined core and
10 µm cladding. We will now see how very durable and strong this fiber is.
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Penlight with batteries
Black rubber penlight boot
2.2 mm (.088 inches) outside diameter jacketed fiber, .75 meter (30 inches) long
Pan of water about 20 cm (8 inches) wide and 5 cm (2 inches) deep*
Hammer*
* Not contained in this kit.
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• Insert one end of the 2.2 mm jacketed optical fiber into the hole in the penlight boot, and turn
the penlight on.
• Wind the remainder of the fiber clockwise in fairly tight 5-cm (2-inch) diameter loops. (It may
help to wind the fiber around a cylindrical object such as a glass, wooden dowel, or the inner
cardboard tube from a roll of paper towels.)
• Observe the light intensity emerging from the fiber end as the fiber is wound.
• Unwind the fiber, then re-wind it, counter
clock-wise, again observing the light coming
from the fiber end.
• Insert the jacketed optical fiber into the pan of
water as you did in earlier experiments and
observe the light coming out from the other
end. Remove the fiber from the water.
• Lay the fiber on a flat surface such as a table,
and strike the mid-section of the fiber
moderately hard with a hammer. As you do this,
observe the amount of light coming out of the
fiber.
• Turn off the penlight and remove the optical
fiber from the rubber boot. Grasping one end of
the fiber in each hand, tug the fiber in opposite
directions in an attempt to break it.
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Winding the optical fiber in coils has no effect
on the light output, no matter which direction it is wound. Coiling and uncoiling the fiber multiple
times doesn't stress it enough to break it (as can happen with copper wire). Placing the fiber in water
has no effect on light transmission, either. Striking the fiber with a hammer has no effect on the output
light intensity unless we hit it extremely hard. Trying to break the fiber by tugging on it also showed
you how tough it is. (Unless you are a very strong person or damaged the fiber with the hammer, you
probably could not break the fiber.)
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It should now be obvious with fiber's strength and durability how it can successfully be bent
around corners, pulled through conduits in tall buildings and installed in tight spots such as the control
panels of automobiles and aircraft.
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