# Sending information on light waves

1. May 23, 2009

### um0123

just likes radios and such. i had a brief discussion with my math teacher on the subject, my math teacher was an electonical engineer at Bell Laboratories for 10 years, and i asked if its possible with radio, cant it be done with any light? He said yes. what i didnt ask him was, how exactly it works, because we were in the middle of class.

so how does information travel on light waves?

bonus quesiton: what would it look like if it was sent through visible light?

2. May 23, 2009

### Born2bwire

It would work the exact same way as with RF waves. Radio waves are the same thing as light, so the same techniques can be used. You modulate the information in by using varations in the frequency, amplitude, and/or phase of the signal.

3. May 23, 2009

### DaleSwanson

As Born2bwire said visible light and radio waves are two types of the same thing. Visible light is just high frequency radio waves, the same techniques could be used.

As for what it would look like, it would depend on how you encoded the information. The two common bands on a radio are AM and FM, or amplitude and frequency modulation. In visible light amplitude is brightness and frequency is color. So if you transmitted information in visible light by modulating the amplitude it would get more and less bright. If you did it by modulating the frequency it would change color.

4. May 23, 2009

### HallsofIvy

Or, for that matter, you can "send information on light" by clicking a flashlight on and off and using Morse code!

5. May 23, 2009

### Defennder

Also see http://en.wikipedia.org/wiki/Optical_fiber" [Broken].

Last edited by a moderator: May 4, 2017
6. May 23, 2009

### Staff: Mentor

A traffic light is another example as are brake lights.

7. May 23, 2009

### Blenton

I stare at lightbulbs wondering if information is possibly encoded there...

8. May 23, 2009

### um0123

so if some perseon had a radio tower that sent out visible light instead of radio light it would make everyone in the area see a tinted color of whatever color he was sending out?
and also, i knew that radio and visible light are both the light, but what i mean is, how is information sent on these waves. We cannot see radio waves and yet they carry information about sound on them. How exactly can it carry this information? what is chaging within the waves to send this information to the reciever?

9. May 23, 2009

### ZapperZ

Staff Emeritus
Er... you do know that optical fiber transmits signal via light, don't you?

Zz.

10. May 23, 2009

### um0123

excuse me, im only in high school... so i dont know exactly what optical fiber is, i have played around with it, and know its used for transmitting internet across the world, and know its used in computers. But i don't know how exactly how it works. im asking how is information sent on light waves. but please, i am very interested in this, and would love to hear more about optical fiber also.

11. May 23, 2009

### ncanac

The answer is essentially what has already been said. Light waves, like radio waves, are just electromagnetic radiation, classified according to their frequency (or wavelength). The general idea of transmitting information is fairly simple. You have a transmitter, which takes some signal, such as a sound or an image for example, and encondes it into a specific sine wave which is transmitted through the air. Your reciever is generally tuned to look for specific frequencies, which it picks up and decodes back into the original information (sound or image, for instance). Both transmitter and reciever are typically what you see everyday as antennas.

The information is encoded in various ways, as was already mentioned. AM is amplitude modulation, where you change the amplitude (you can sort of think of this as the "volume" or "brightness" of the wave). FM is frequency modualation, where you just slightly modulate the frequency. There are other ways to do it too, such as PM or pulse modulation where you basically turn the signal on and off. When you really think about it, these modulations in the signal are no different than the simple examples of morse code or the traffic light already used. There is a kind of "key" by which you can encode and decode the signals, and this is done through various kinds of electronic circuits, the design of which is considerably more complex than could be described here.

12. May 23, 2009

### HallsofIvy

In fact, if you ask a question, conveying information by sound waves, and that person nods "yes", information has been conveyed to you via light!

13. May 23, 2009

### um0123

not to be rude, but...duh...

anyway, thanks for the information, i want to do soem more research on this, though. It has always intereted me how you get picture on your TV just from electonic cables, or how sound can be picked up from radio wave signals.

14. May 23, 2009

### Pengwuino

Well remember, the same signals that go across telecommunication lines and cable tv lines aren't the signals that pop up on your TV or telephone speaker or what have you. The signals are interpreted by electrical equipment that tells, in a television for example, a system of projector, magnets, and other things how to display an imagine using actual light thatyou can see. In radio's case, again, your electrical device, ie your radio, picks up radio waves and interprets them into signals that run the speakers which are actually responsible for creating sound.

15. May 23, 2009

### um0123

i understand

16. May 23, 2009

### Buckleymanor

Try the TV or pictures for a change.

17. May 24, 2009

### Staff: Mentor

Yes, if radio towers broadcasted in the visible then you would be able to see the towers shine some color. For AM stations the brightness of the tower would flicker, and for AM stations the color of the tower would flicker. In both cases the sound information is encoded in the flickering.

I think Born2bwire's answer is complete.
But also important is that you always have to establish some convention so that the sender encodes the information and the reciever decodes the same information. For example, a traffic light encodes information about the required action in both the frequency (color) and amplitude (brightness) of the traffic lights. If some traffic light were to use a blue light to encode a "Stop" message then the decoding would not work correctly and the information would not be transfered. Similarly with any other information transmission system. There are an unlimited number of possible conventions.