# Communicating with Light

## 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

• Sound recorder (phone)
• Software (Matlab)
• No risk

Procedure

• Record an audio file
• Plot frequency / time of the audio file
• 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

https://www.mathworks.com/help/signal/ug/spectrogram-computation-in-signal-analyzer.html