Science News - article on Quantum Crypto

[jah at alien.bt.co.uk]

> I am not sure this is correct. In-line optical amplifiers work by
> stimulated emission like a laser rod. There is no intermediate
> electronic stage. The amplifier is a section of fibre that is doped
> with a rare earth element. The rare earth atoms are boosted into a 
metastable
> high energy state using a power source around the fibre. Passing signals
> (photons) stimulate the decays of the metastable states releasing more
> photons and boosting the signal. I am not sure what the effect of this on 
the
> polarisation characteristics of the signal is but my *hunch* is that the
> polarisation characteristics would be preserved in the amplified signal.
> 
> Sherry
> 
> ps Any laser physicists in the house?

Dr. Simon Phoenix (my resident quantum crypto guru) says no, you can't
use em - you have to build secure repeaters. Simon has been doing this
sort of thing in the Lab for years. He's simon at alien.bt.co.uk if you want
to probe him gently.

/.J

BTW: You can build  an Erbium doped amp that is 'transparent' to your
secure channel.