Re: super-fast freespace optics last-mile tech

From: Doug Jones (
Date: Thu Mar 02 2000 - 17:01:57 MST

"Eliezer S. Yudkowsky" wrote:
> Brian Atkins wrote:
> >
> > Here you can read a patent app from a very secretive Seattle company:
> >
> >
> >
> > this looks to me like a very amazing advance in the speeds that people
> > will be able to access the net in the near future. Basically you slap
> > some of these lasers onto cell towers around a city and you get a super-
> > fast network (the cell towers can communicate with each other, so no
> > land lines needed) providing anywhere from 1.5mbit up to 10gbit to
> > individual users.
> I'm skeptical. The whole reason for fiber optic cables is that air,
> dust, water drops, et cetera scatter laser light beyond retrieval. I
> don't see any obvious way to get around that limitation; you'd have to
> use gamma-ray lasers, or neutrino lasers, or tachyon lasers, or such
> high-powered ordinary lasers that they'd punch through intervening
> airplanes as well as dust particles, and even then I'm not sure you
> could get 1MHz useful data out of it. If this company has invented a
> workaround, they *deserve* a 20-year patent. But I'll believe it when I
> see it.

This application probably *depends* on multipath scattering to get a
robust channel resistant to environmental effects- the transmitters are
likely to project their power in a fan toward the horizon, and likewise
the receivers have a wide acceptance angle. Very narrowband optical
filters would improve S/N and pseudorandom encoding would eliminate
echoes & reduce network collisions.

After all, an ideal information channel looks like noise if you don't
have the key...

Doug Jones
Rocket Plumber, XCOR Aerospace

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