We have gotten many requests for projects involving fiber optic communications for science fairs and K-12 science class projects. We thought we'd share with you the projects we developed for our own kids in the scouts and has been used in classrooms and science fairs. We've added a few more advanced exercises to enhance it for older students.
carries signals as pulses of light while copper cables carry signals as
pulses of electrons. As the photo below by AT&T from
the 1970s showed, one hair-thin fiber can carry more signals than the
giant copper telephone cable in the photo. Today's fibers can carry
millions of times the data that that fiber could 40 years ago!
Here are some
fiber optics projects you can do in class or for a science fair.
How Fiber Transmits Signals By Light (Grades K-12)
This is a demonstration of how communications signals travel as pulses of light over fiber optics, creating a fiber optic telegraph that sends signals as light and can send Morse code. Morse code was the signalling system used by the original telegraph in the middle of the 19th century, creating the first long distance communications.
Reference: The Victorian Internet: The Remarkable Story of the Telegraph and the Nineteenth Century's On-line Pioneers by Tom Standage
The project uses plastic optical fiber (POF) which has a large core ( ~1 mm ) and transmits light best at 650 nm, or bright red light so it is easily visible. Regular communications fiber optics uses smaller glass fiber and transmits in the infrared light for greater efficiency. The original project uses a small red LED (available from electronic hobby stores or online) driven by a 9V battery. The diagram was drawn by a 6th grade student who contacted us for help through this web page in 1997, used our idea for his project, then drew the diagram below on his computer. (Yes, that was state of the art computer graphics way back then!)
can duplicate this demonstration with your own equipment.
can easily duplicate this experiment with a short length of plastic
fiber (samples available from FOA or you can purchase 1mm plastic
optical fiber online) and a simple, inexpensive laser pointer. Couple
the fiber to the laser pointer (some tape helps increase the fiber
diameter to fit snugly into the end of the laser pointer.) Use the
switch on the laser pointer to pulse the light on/off to create pulses
of light that are transmitted from one end of the fiber to the other.
If you are doing a science project, below are some background facts that can help explain what is happening.
the explanation below, we explain some principles of fiber optics and
give you some questions to answer. Those questions are in bold
type. Answers will be at the end of the page. We also
suggest additional activities that can be good for science projects
- those comments are in italic type.
The Science Behind Fiber Optics (Grades K-12)
Light Travels In An Optical Fiber,
Total Internal Reflection
transmits light using an optical principle called total internal
reflection that keeps the light in the core of the fiber.
Learn more about total
internal reflection here - (Grades
7-12). Students who have taken trigonometry can
see the equations to calculate total internal reflection in optical
fiber, useful for a science project.
You can duplicate this experiment for your class or science project. You need an acrylic plastic rod about 25mm (1 inch) diameter (available online) and a green laser pointer. The green pointer is more visible than the regular red laser pointer. To get light into the plastic rod, you need to polish the end of the rod which is usually just sawed off. Start with fine sandpaper from a hardware store - 1200 to 3000 grit - to remove the saw marks, then polish the end with polishing compound - the same stuff used to remove scratches and polish cars. It should have a mirror-like finish for best results. Once the rod is polished, you can see the laser pointer beam in the plastic rod like the demonstration above. Lower room lights to see it better. At a science fair you can paint the inside of a box black and cut holes in each end for the plastic rod to fit through it to block outside light and improve visibility.
Transmitting Signals As Pulses Of Light (With Math - Grades 7-12)
FOA Video: Fiber
A fiber optic link
has a transmitter that converts an electrical signal from a
computer or phone or video camera to an optical signal. The signal is
transmitted through an optical fiber to a receiver that converts
the optical signal back to an electrical signal so it can be displayed,
heard or a video watched.
signals can be analog (continually varying) or digital (an analog signal
converted into digital bits). Most signals today are digital.
demonstration with plastic fiber and a laser pointer is an example of
how digital signals are transmitted over fiber optics. Each time you
press the button on the laser pointer, you are sending a pulse of
light down the fiber.
finger however is very slow. Digital signals can be very fast.
Your Internet connection is probably 5-25 million bits per second
(5-25,000,000). Long distance fiber optic cables operate at 1 billion
(1,000,000,000) up to 100 billion (100,000,000,000) bits per second.
Communications At The Speed Of Light (Grades 7-12)
you can make about light transmission in optical fiber. Answers
The speed of light
in a vacuum like space is approximately 300,000
kilometers per second or 186,000 miles per second.
That means the
light from Earth's Moon which is 250,000 miles away takes about 250,000
miles divided by 186,000 miles per second or 1.35 seconds to reach
Earth. Radio communications travel at the same speed in space, so when
NASA communicated with the Apollo astronauts walking on the moon in
1969, a conversation would take 2.7 seconds travel time for each reply.
does light take to get from our Sun to the Earth?
_______________ The Sun is approximately
150million km (150,000,000) or 93million miles (93,000,000). You can
figure it out with the information above.
How far away is our nearest star, Alpha Centauri? It is 4.2 light years away. How many kilometers or miles is that? _______________ Calculate how long the trip would take in a car (100 km/hour), airplane(1000 km/hour) or rocketship (the escape velocity from Earth's surface is about 40,270 km/h or 25,020 mph.)
But here is an important physical principle - the speed of light is the speed of light in a vacuum like space. Light slows down in transparent materials like glass. In fact the speed of light in glass or clear plastic defines an important physical characteristic of the material called it's "index of refraction." The index of refraction is calculated by:Speed of light in a vacuum (c) = speed of light in the optical material (v) X the index of refraction (n)
Thus c = v x n or n = c / v or v = c / nThe index of refraction of glass is around 1.5, varying a bit for different types of glass. So what is the speed of light in a glass or plastic optical fiber? _______________ Knowing that, how long would it take a fiber optic cable to transmit signals from New York to London, 5585 km or 3470 miles.
How long is the
light pulse in an optical fiber? ________
You can actually calculate and visualize how big an optical pulse is. You calculated above that light travels in a fiber at 200,000 kilometers per second in an optical fiber. A kilometer is 1,000 meters, so that speed is 200,000,000 or 200 million meters per second. If a signal has 1 billion (1,000,000,000) pulses per second, how far apart are the pulses?
In one second, a pulse travels 200,000,000 meters. In that same second there are 1 billion (1,000,000,000) pulses passing along that distance of the fiber, so the distance between pulses is:
= 0.2 meters between pulses. 0.2 meters is 20 centimeters, 200
millimeters or about 8 inches in the English system.
Then a system
sending signals at 1 billion bits per second (we call that 1 gigabit per
second) has pulses every 20 cm (8 inches) in the fiber.
Wavelengths Of Light Used In Fiber Optics (Grades 7-12)
Light is defined
by its wavelength, or in the range of sensitivity of the human eye, what
we call color. The eye has evolved to be sensitive to light in the
range of the output of our Sun, which is handy since it makes it easy
for us to see in the Sun's light. But optical fiber works better at
longer wavelengths of light, what we call the infrared range, because
the attenuation of the fiber is less in the infrared and signals can go
farther. The diagram below shows the attenuation of a typical optical
Two factors cause fiber attenuation, scattering and absorption. Absorption is due to certain molecules absorbing light at specific wavelengths. In glass fiber this is mainly from water in the fiber after manufacture. Scattering is a matter of light bouncing off atoms and molecules which is very dependent on the wavelength of light. Scattering is much less at longer wavelengths in the infrared so fiber is used at those wavelengths. Scattering is very high in shorter wavelengths and on a clear day you can see evidence of this yourself. Just look up at the sky. The light from the Sun entering Earth's atmosphere is scattered mostly in the blue wavelengths so the sky takes on a blue hue. At sunset the sun gets red due to the fact that the blue light is attenuated more by the atmosphere - at sunset, the Sun is near the horizon and is shining through more than 6 times as much air as at noon! (Make a drawing of the earth with a layer of atmosphere and prove this for yourself.)
Sending Signals At Different Wavelengths of Light (Grades 7-12)
Another "trick" we use in fiber optics is sending light of several wavelengths through the same optical fiber at the same time as shown in this photo. Light of different colors can coexist in the same medium - that's how we can see your red short and blue pants at the same time. In fiber, we can put up to about 100 different wavelengths of light down the same fiber. It allows us to expand the bandwidth of the fiber by 100 times!
Special optical modules called couplers combine light of several wavelengths into one fiber and separate them at the far end.
Here is how it
looks in action. For a source we use two laser pointers as the sources,
one red and one green, and send light from them down a fiber (or the
large plastic rod we show above) at the same time.
Science Project From 1997
Teachers: see our free online PPT presentation - an introduction to fiber optics or view a similar presentation on YouTube.
Light travels 300,000 km per second
Multiply times 60 seconds in a minute and light travels 18,000,000 km per minute (that's 18 million km per minute)
Multiply times 60 minutes in a hour and light travels 1,080,000,000 km per hour (that's 1.088 billion km per hour)Multiply times 24 hours in a day and light travels 25,920,000,000 km per day (that's 25.92 billion km per day in the US, but 25,920 million in countries that use the metric system - yes even that's different! A billion in the US is 1,000,000,000 - 1 and 9 zeroes or 10 to the 9th power, while in the metric world, a billion is 1,000,000,000,000 - 1 and 12 zeroes or 10 to the 9th power)
Multiply by 365.25 days per year, and light travels 9,467,280,000,000 km per year. That's 9.46728 trillion km in the US (about 5.9 trillion miles) or 9.46728 billion km in the metric world.
So if Alpha Centauri is 4.2 light years away, it's 39.76 trillion km away. (24.71 trillion miles.)
You can figure out how long the trip would take in a car, airplane or rocketship.
what is the speed of light in glass or plastic like an optical
From our equations
= c / n.
For n = 1.5, v =
300,000 / 1.5 = 200,000 kilometers per second.
In American units (we're practically the only country still using the "english system" of inches/feet/yards/miles instead of the "metric system" or mm/cm/m/km - and fiber optics is all metric), v = c / n or 186,000 / 1.5 or 124,000 miles per second.
Knowing that, how
long would it take a fiber optic cable to transmit signals from New York
to London, 5585 km or 3470 miles.