PASCO WA-9316A Complete Microwave Optics System - Manual (Page 27)

013-13906B Experiment 10: Fiber Optics
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Experiment 10: Fiber Optics
Equipment Needed:
Introduction
Light can propagate through empty space, but it can also propagate well through certain materials, such as glass. In fiber
optics, a thin, flexible glass tube functions as a transmission line for light from a laser, much as a copper wire can function as a
transmission line for electrical impulses. In the same way that variation of the electrical impulses can carry information
through the copper wire (for example as a phone message), variation in the intensity of the laser light can carry information
through the glass tube.
Purpose
In this experiment you will investigate the phenomenon of total internal reflection (as related to “fiber optics”).
Procedure
1. Align the Transmitter and Receiver directly across from each other on the Goniometer, and adjust the Receiver controls
for a readable signal.
2. Fill a tubular plastic bag with styrene pellets (tie the end or use a rubber band). Place one end of the bag in the Transmitter
horn. What happens to the meter reading? Now place the other end in the Receiver horn. How does the intensity of the
detected signal compare to the intensity when the bag is not used?
3. Remove the plastic bag and turn the Rotatable Goniometer arm until no meter deflection appears. Place one end of the bag
in the Transmitter horn, the other in the Receiver horn. Note the meter reading.
4. Vary the radius of curvature of the plastic bag. How does this effect the signal strength? Does the signal vary gradually or
suddenly as the radial curvature of the plastic bag changes? Find the radius of curvature at which the signal begins to drop
significantly.
Questions
1. Check your textbook for information on Total Internal Reflection. Based on the radial curvature when the signal begins to
show attenuation as it passes through the plastic bag, determine the angle of total internal reflection for the styrene pellets.
Can you use this value to determine the index of refraction of the styrene pellets?
2. Would you expect the plastic bag filled with styrene pellets to work the same with radiation at optical frequencies? Why?
Item Item
Transmitter Goniometer
Receiver Styrene Pellets
Tubular Plastic Bags