Photonic Links Lab - 1 -
Optical Voice Link
Courtlan Hall & Melanie Jasper
Cosmos UC Davis, Cluster 2
Fundamental Science and Technological Applications
Niels Gronbech Jensen and Diego Yankelevich
July 30, 2007
Photonic Links Lab - 2 Abstract
Sound waves can be transformed into optical waves that travel much faster.
Sound waves travel at a speed on 344 meters per second and optical waves travel at 3.0 x
10^8 meter per second. We measured the optical bandwidth, because if the frequencies of
the sound waves are too high then the optical fibers will not transmit the information. The
amplitude of the graph decreased as the frequency increased. We also measured the
difference in phases between to sinusoidal graphs by multiplying the frequency by the
change in time by two pi. We noticed that the radians grew as the frequency of the wave
was increased.
Introduction
A fiber optic cable if created from a mixture of glass and plastic. These cables are
capable of transmitting light across large distances at very fast speeds. The cables have a
core, which is the glass, the cladding surrounding the core. The cladding creates a better
refractive index making it easier for the light to travels through without propagating
much. Then the cladding is covered by Kevlar fibers to provide strength to the cable. And
finally the cable is wrapped in rubber to keep away dirt, water and anything else that
might interfere.
Photonic Links Lab - 3 Figure 1 A Fiber Optic Cable
Fiber optic cables carry data all around the world. Optical waves have the ability
to carry data, depending on the frequency and amplitude. Optical fibers have a certain
bandwidth that the must operate in. if the frequency is too high for the bandwidth, then
the amplitude will be so small that it would be almost impossible to receive any data
through the waves.
Sound waves travel at a much slower rate than optical waves. The two waves are
very different. Sound waves are similar to a ripple in a pond, they expand and diverge
making it difficult to carry information on them. However, optical waves are sinusoidal.
They travel extremely fast, at around 3.0 x 10^8 meters per second in a vacuum. Optical
fibers have revolutionized communication. It is now much faster and easier to send and
receive messages across long distances. Sound waves in America can now be
transformed into optical waves, and then be sent through optical fibers to Europe. In
Europe they are transformed back into sound waves and the information is received in a
fraction of the time it would take for radio waves to transmit the information.
Photonic Links Lab - 4 -
Figure 2 The web of fiber optic cables across the oceans
In this lab we created a fiber optic link that was capable of transferring sound
waves through fiber optic cables by transforming them into light waves, and by using an
oscilloscope we measured the light bandwidth and phase difference between two
sinusoidal.
Materials
Wire cutters
Small Phillips screwdriver
1ml water
25-watt soldering iron
two 9V batteries
Razor blade
Needle-nose pliers
Wrench
Rosin-core solder
18-gauge wire-stripper
Dual-trace oscilloscope
Transmitter
BNC (T) connector
Alligator clamps
Receiver
Fiber optic cable
Photonic Links Lab - 5 -
Methods
To begin the lab we built a transmitter and receiver from an optical voice link kit.
We followed the kit instruction booklet for assembly. We soldered all the parts to the
chip and inserted 9-volt batteries for the power source. Then we connected the transmitter
to the receiver with a fiber optic cable and tested the link by speaking into the
microphone on the transmitter and listening for our voice come out of the speaker on the
receiver. Then we attached alligator clams to the speaker and attached it to the
oscilloscope and signal generator to find the sinusoidal graph. We measured the
bandwidth of the optical voice link kit by measuring at what frequency the amplitude
became too small to read. We also measured the difference in radians between two
sinusoidal graphs at different frequencies.
Photonic Links Lab - 6 Frequency Hz Amplitude mV
100
300
1000
3000
5000
10000
30000
50000
100000
300000
500000
815
810
800
750
500
375
100
75
45
15
5
Amplitude (mV)
Amplitude of a wave as a
function of frequency
1000
800
600
400
200
0
Series1
1
100
10000
Frequency
100000
0
Photonic Links Lab - 7 -
Frequency Hz
100
1000
5000
10000
50000
100000
Radians
1.319
6.283
12.566
4.712
14.1368
62.83
Frequency vs Radians
70
60
R a d ia n s
50
40
30
20
10
0
1
10
100
1000
Frequency (Hz)
10000
100000
Photonic Links Lab - 8 -
Analysis
In the first experiment we discovered that the photonic link worked well. Though
it also had to be very exact. If two pieces of wire were just barely touching then it would
not work. We also had to tune it with a knob attached to the transmitter. In the end our
photonic link worked well.
Once we got it working we tried to test the frequency that the link worked with.
We steadily raised the frequency until we were unable to read it. We discovered that the
link worked at a wide range of frequencies. We were able to read it all the way until
500,000 Hz.
For the last experiment we measured the difference of radians between two
sinusoidal graphs. We discovered that the difference becomes more drastic between
10,000 and 100,000 Hz.
Conclusion
We discovered that an even our simple optical links worked at a wide variety of
frequencies. It used the laser running through the optical cable to transmit information.
The optical link worked well and has good potential to become more commonly used in
the future. It has advantages over regular electric cables because it is unaffected by the
weather. The optical links work well to transmit information.