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When I see a big radio antenna, I like to imagine it's a giant incandescent light bulb filament in the vertical, but of a invisible light. So that it "glows" the radio, performing oscillations which contains all the music/voice information.

But at the reverse, is it possible to create a practical experiment which modulates (or something) an analog audio signal and transmits it by glowing some sort of light, then have a antenna or sensor to pick it up and reproduce the signal to a speaker?

Is it possible to use a mono pole antenna to detect light?

fschuindt
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2 Answers2

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But at the reverse, is it possible to create a practical experiment which modulates (or something) an analog audio signal and transmits it by glowing some sort of light, then have a antenna or sensor to pick it up and reproduce the signal to a speaker?

Yes, in principle.

Analog modulation of optical signals is not super common, but it is done, for example in many CATV-over-optical-fiber systems.

Free-space optical communication is commonly be done between a hand-held remote control and a television set.

Optical communication of audio signals is done in TOSLINK interconnect.

There's no technological reason these things aren't all combined into a single analog, free-space, audio communication system, only economic reasons: We have cheaper ways of doing it so nobody has bothered to commercialize such a thing.

It would be pretty easy to set up a class-room demonstration where an audio signal is sent to an LED, which illuminates a photodiode a few cm away, which connects through an amplifier to drive a speaker, if you wanted to demonstrate such a thing.

Even with much older technology, there was the photophone developed by Alexander Graham Bell.

The Photon
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  • "Free-space optical communication is commonly be done between a hand-held remote control and a television set." - that's infrared, though, not visible light. – John Dvorak Jan 29 '19 at 16:53
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    @JohnDvorak, OP didn't specify visible light, and there's really very little practical difference between visible and IR. There's no reason a TV remote couldn't be done with visible light, except that it would be annoying to the user. – The Photon Jan 29 '19 at 16:54
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Various spy agencies have used this technique to eavesdrop on conversations from some distance away. When people are talking inside a room that has windows, there is a very tiny vibration of the windows as the sound waves from the voices bounce off of those windows. It is possible to reflect a laser beam off of a vibrating window, receive the reflected beam, and recover the sound waves from the modulation contained in that beam.

David White
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  • You're right. In fact, this video: https://www.youtube.com/watch?v=FKXOucXB4a8 shows something similar in practice. But this case is kinda far from what I was asking, which is more something like a "radio" station with electric powered transmitters and a antenna transmitting to a "radio" receiver with yet another antenna.

    One important point here is the ability of a mono pole antenna to resonate a given frequency and deliver it as a current.

    The question asked if it's possible with visible light.

     – fschuindt Jan 31 '19 at 15:18
  • @fschuindt, I maintain that the answer is "yes", it's possible with visible light. What you are describing is implementation details, and those would have to be worked out based on what system you chose to use for this application. – David White Jan 31 '19 at 17:57