Optical Cellphones

foondog writes "Here is a story over at News.com about optical cellphones. It seems that the Department of Defense has given a grant to the University of California to develop optical cellphones that are faster and more secure. This sounds a little strange to me since you would need a line of site with no obstacles in the way to use this. The article doesn't explain how this might work."

Comments

Re:Using a laser?

[spike hay]

Lasers are out of the question for this. Lasers produce a very narrow collumnated beam. No good for cellphones. Probably something more along the line of bright LEDs would be better.

Big lasers, with lots of power. Could be dangerous.

It wouldn't need to be high power at all. Hobbyists have been experimenting with optical wireless communications for several years. It's not dangerous. Although the hobbyists use fixed points with either lasers (milliwatt power) or focused LEDs to transmit light. This DoD thing seems pretty crackpot to me. Why not just use high frequency microwaves? (Probably around 500 ghz to 1 thz) You have all the bandwidth you could ever use for cellphones in that range, and you wouldn't need fancy optical devices like super-sensitive photodetectors.

The East German secret service used this

[uradu]

Not an actual cell phone, but a point-to-point intercom involving binoculars and infrared transmissions. The voice was converted to (analog) IR light and transmitted through optics that created a very narrow beam. At the other end, the IR receiver was mounted in the eye piece of the binoculars and converted the light back to sound. The two devices had to be aimed very accurately at each other. That way a spy in the west could communicate with his pimp in the east across the border with very low probability of interception. They actually had this on the History Channel a few years back.

Re:Optical Communications to Keep Bombs Away

[Michael Woodhams]

The problem you describe is not "radio broadcast vs optical narrow beam", it is "broadcast vs narrow beam". Once I've decided to go narrow beam for these reasons, why would I go optical rather than microwave?

(The beam divergence is inversely proportional to the number of wavelengths wide your transmitter/reflector is, which means that smaller wavelength requires a smaller transmitter apperature to achieve a given beam divergence, but surely microwaves are good enough, and have much better penetration.)