From: jah@alien.bt.co.uk
Date: Mon, 19 Feb 1996 19:35:34 +0800
To: cypherpunks@toad.com
Subject: Re: Science News - article on Quantum Crypto
Message-ID: <9526.199602191103@orb.alien.bt.co.uk>
MIME-Version: 1.0
Content-Type: text/plain



> 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@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.