Radio communicattion in lower wavelength

[Seanskahn]

Hi community.

Once again, a stupid question:

if radio waves are electromagneetic waves, generating an electric field in the antenna, then why can't one just shine visual light (also electrromagnetic waves) on same antenna and use that for communication?

thanks
s

 

[cjameshuff]

Once again, a stupid question:

if radio waves are electromagneetic waves, generating an electric field in the antenna, then why can't one just shine visual light (also electrromagnetic waves) on same antenna and use that for communication?

Not a stupid question. Receiving antennas are close in length to the wavelengths they receive, or to a small integer division of that wavelength...quarter-wave antennas, for example. They work by "ringing" in response to electromagnetic radiation hitting them...some antennas are more specific than others, but the wavelength has to be at least roughly matched to the antenna's length. The wavelength at 10 MHz is 30 meters, at 2.4 GHz it's 12.5 cm, and by the time you get to the visible range it's less than a micron...700-some nm for deep red. The circuitry hooked up to the antenna is also limited in how fast it can operate, and visible light has a frequency of about 0.5 petahertz.

It's all about scale and speed...microscopic antennas that work at optical frequencies have been made in the lab. Arrays of similar structures have been used to make the metamaterials that the media insists on calling "invisibility cloaks", and might end up being very useful in optical communications, computing, and scientific instruments.