Communicating with Light

Contributed by Jon Luntzel

Introduction

How do you hear your friends when you’re talking to them on the computer, gaming, on the phone?
How come messages can go so quick even though the earth is so big?
How can a device we’ve built keep track of a signal, when there’s so much information in it? Does it know exactly what’s happening at every fraction of a second?
How fast could it go?
How might we detect small packets of information such as light? Can you think of any examples of where we need to know if something is there or not?

Materials

Procedure

Record an audio file
Plot frequency / time of the audio file
Read it in using audioread(filename)
Divide the signal into equally sized segments (signal analyzer toolbox) choose no overlap for simplicity
compute the power spectrum of each segment, then take the mean frequency of each segment to build a discrete signal
Plot frequency / time again
Convert each segment into binary based on frequency, send the string to someone else, have them reconstruct it (visual of fiber optic signal)
Other person saves the signal as a .wav file (use the audiowrite method) and play it back, choosing different segment sizes to show the effect

Physics Concepts and Questions

How would this help us send a signal using a technique like fiber optics?
Signal compression. Explain how it’s important, because finite resources, technological constraints, convenience
Digital vs. Analog

Conclusions and Further Investigations

How would we do this for an image, or other kind of message?
What might be a short way of telling the other person what they need to know to reconstruct it? General method for dealing with any binary signal?

Citations