Instructional Kit: Light, Color & Lasers
Fiber Optics and Telecommunications
MathScience Innovation Center Staff
Funded by the MathScience Innovation Center
Major
Understanding
When light waves pass from a less dense medium such as air to a denser
medium such as water, the waves will bend toward the normal and slow
down. When passing from a dense medium to a less dense medium, the
opposite will happen. The greater the angle of the incidence ray is to the
normal line, the more the light is reflected than refracted. The critical angle is
the angle where all light is reflected within the medium. This is called total
internal reflection and is how fiber optics works.
Background
Information
Although light travels in a straight line, it can be reflected internally at a
boundary between two substances such as the water’s edge and inside special
optical fiber cable. This series of reflections is much like a bullet ricocheting
down a steel pipe. Optical fibers are useful for getting light to inaccessible
places. This phenomenon of internal reflection allows light to be directed
anywhere a wire can go including the veins and arteries of the human body or
into the interior of machine engines.
Optical fibers are important in communications because they are more
efficient and less expensive than copper wire or coaxial cable. They are
replacing electric circuits in communications technology more and more.
For more information on the internal reflection of light and fiber optics, refer
to the book, Stop Faking It! Light, which is provided in the kit. Go to Chapter
1, pages 10-12.
Standards of
Learning
Virginia Standards of Learning: Science 5.1, 5.3
National Science Education Standards:
Level K-4 Physical Science (Light, heat, electricity, and magnetism)
Level 5-8 Physical Science (Properties and changes of properties in matter)
Material Needed
Light, Color & Lasers
Materials provided by the kit:
Lumirod (Lucite tube)
Fiber Optic flashlight
Optical Voice Link kit
Laser pointer
Flashlight
Light socket and incandescent bulb (25 watt)
Comb
http://mathinscience.info
© MathScience Innovation Center 2006
1
Safety
1. The laser pointers provided in this instructional kit are Class 2 lasers and
are safe for student use. However, please read and follow the safety label
on the laser pointer.
• Closely monitor student use of laser pointers.
• Do not stare directly at the laser beam emitted by the pointer.
• Be careful when shining onto reflective surfaces to prevent
unexpected reflection into the eyes.
2. The incandescent bulb (25 watt) will become hot. Use caution when using
it.
Procedures
1. Internal Reflection Demonstration.
• Aim the flashlight at one end of the spiral Lumirod.
• Observe the internal reflection of the light as it travels down the tube
and exits the opposite end.
The “curved path” of the light is really an example of light energy
traveling in short straight lines (internal reflection).
2. Fiber Optic Demonstration
• Turn on the fiber optic flashlight.
• Observe the light energy exit the end of the fibers.
Each filament reflects the light internally until it exits the end of the
filament.
Light, Color & Lasers
http://mathinscience.info
© MathScience Innovation Center 2006
2
3. Fiber Optics and Telecommunications Demonstration I
• Using the Optical Voice Link kit, connect the transmitter and the
receiver with the coiled fiber optic cable. The transmitter uses a LED
light source that is activated when the red button is depressed.
• Turn on the receiver and adjust the volume to about halfway. The
receiver detects light energy by means of a photo diode. See picture.
•
•
•
Press the red button on the transmitter to activate the LED light.
As the light energy travels down the fiber optic cable, the receiver will
interpret the signal as audible sound.
Next, remove the transmitter and point the free end of the fiber towards
various light sources such as a flashlight, incandescent bulb, fluorescent
bulb, or laser pointer. See picture.
Again, the light energy travels down the fiber optic cable and is
interpreted by the receiver as sound energy. The signal varies with the
intensity of the light source. For example, compare the signal created
with the flashlight beam with the signal created by the laser beam.
Would the coherent light of the laser beam be more effective for
transmitting information by fiber optics?
Light, Color & Lasers
http://mathinscience.info
© MathScience Innovation Center 2006
3
4. Fiber Optic and Telecommunications Demonstration II
• Point the free end of the fiber optic cable toward the laser pointer and
turn it on. Again, the light energy travels down the fiber optic cable and
is interpreted by the receiver as sound energy.
•
•
•
Extension
Assessment
Place a comb between the laser beam and the fiber optic cable.
Modulate (change) the beam by moving the comb back and forth in
front of the beam. By interrupting the laser beam, messages, music,
images or any desired signal can be encoded on the light. This
encoding is similar to a bar code. A laser beam is used to scan the
particular pattern of a bar code used for identification or the price of
an item.
Watch a video of the laser beam being modulated by a comb.
Students may do more research about fiber optics on the internet at the
following websites:
www.howstuffworks.com/fiber-optic.htm This site provides a good
explanation of fiber optics.
www.webopedia.com/TERM/f/fiber_optics.html
www.wikipedia.org/wiki/Fiber_optics Both of these sites give a good
definition of fiber optics but can become very technical at times. There are
good diagrams that explain total internal reflection of light.
1. Students may draw a sketch or write a short paragraph that describes how
light energy can be made to travel down the Lucite tube or the filaments of
the fiber optic flashlight. The sketch or paragraph should describe what
happens when light waves are reflected internally in a medium.
2. Go to http://rubistar.4teachers.org/rubistar/ to construct a rubric to assess
student understanding of internal reflection of light.
Light, Color & Lasers
http://mathinscience.info
© MathScience Innovation Center 2006
4