Communicating with Light

Communicating with Light

Contributed by Jon Luntzel


  • 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?


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


  • 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?