Elenco Fiber Optics Voice Data Kit - Manual (Page 24)

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Understanding light at the very smallest level — atomic
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An atom consists of a small and dense nucleus,
surrounded by electrons — the same particles that
produce electric currents. Electrons circle the
nucleus at difference distances. The farther they are
from the nucleus, the more energy they have. If an
electron moves from an outer orbit to a closer one, it
loses energy. This energy is released as a particle of
light called a "photon." In most atoms there are
many electrons and many different energy levels.
The color of light that each electron can produce
depends on how much energy the electron loses
while falling from one orbit to an other.
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Red-colored 1 mm (.04 inch) diameter optical
fiber
Green-colored 1 mm (.04 inch) diameter
optical fiber
3 mm (1/8 inch) black heat shrink tubing, 15 cm (6 inches) long
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• Lay the red- and green-colored fibers on a table and observe their brightness and color, from all
sides and angles. Does the fiber end appear different than the side?
• Find a room which you can completely darken. With the lights off and window coverings closed,
do the green and red fibers continue to glow ("fluoresce")?
• Turn the room lights back on and open any window coverings. Insert one end of the red fiber
inside the heat shrink tubing and slide the fiber slowly into it while observing the exposed fiber
end. How does the brightness of the exposed fiber end change as the fiber slides into the black
tubing? Repeat with the green fiber.
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The center portion or "core" of both colored fibers appears to "glow" as if the fibers were
producing red or green light. The fibers' sides are uniform in color, but dull. As the room light
diminishes, the glow from the fiber ends decreases. In a totally dark room the fiber will stop glowing.
As the fibers are inserted into the heat shrink tubing the glow from the exposed end does not change at
first. When the fiber exposed from the tubing is 5 cm (2 inches) or less, the brightness appearing from
the fiber end begins to decrease. When the fiber is surrounded by the walls of the heat shrink, the fiber
end will be very dim.
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In this special fiber material, atoms absorb light of one color, and almost immediately release the
energy as light of another color. Many substances fluoresce when ultraviolet light strikes them. We can
not actually see ultraviolet, but we can see the lower-energy light that fluorescence produces.
The red- and green-colored fiber contains a central core which includes a material with
fluorescent properties. The fluorescent core absorbs blue and ultra-violet light from all directions.
Having absorbed energy, it radiates this energy in the form of red or green light (depending on the
material in its core). The cladding on the outside of the fiber core traps the radiated light and guides it
toward the ends, which is why they glow and the sides do not.
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These types of fibers are often used in radiation protection and measuring devices. The
fluorescent material absorbs high-energy alpha, beta and gamma radiation and converts that energy
into forms measurable by conventional light detectors.
Electron orbit
Nucleus
Photon of short-
wavelength ligth given off
by electron falling two
energy levels
Photon of long-wavelength
ligth given off by electron
falling one energy level
Path of electron
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