The implications for cryptography are rather cool. I don't *think* these doped optical amplifiers interfere with so-called quantum cryptography (not to be confused with quantum computing, of course). If I remember my SciAm back issues, quantum crypto is cool, because if anyone touches the signal from Alice to Bob they're detected immediately. Or, is it that the signal drops? Can't remember which. Anyway, you need uninterrupted fiber to do QC, and that's what you have with optical non-switched amplification, whether you're disturbing the photons is another story. Anyone here know for sure? I remember discussion about this, but I don't remember the answer.

I am not an expert in the *exact* physics of quantum crypto or of optical amplifiers, but I do have a least a college "modern physics" level of understanding of both. (and write software for a lot of fiber optics hardware) Quantum Crypto depends on the fact that you can't observe the photons without disturbing them, and that this disturbance would be detectable at the receiver. (i.e. Heisenberg's uncertainty principle at work) Optical Amplifiers work by receiving a relatively small number of photons, and passing them through a device where each photon creates in effect a cascade of photons to be generated thereby amplifying the signal. Now, this cascade mechanism in itself might be enough "measurement" to cause problems - but I don't know - and won't persue this avenue further. The problem is that while the waveform will be propagated, the orignal photons won't necessarily make it from one end to the other. Without these original photons making the entire journey I don't see how the quantum crypto would work. There are also pratical limitations on the number of optical amplifiers you can have in a system before having an electrical regenerator. Typical numbers are around 5 amplifiers, eaching going about 80km. This doesn't allow for around the world pure glass communications. ;-( Dan -------------------------------------------------------------------------- Dan Oelke - droelke@aud.alcatel.com Alcatel Telecom, Richardson, TX There's a Wocket in my Pocket, And a Findow in my Window, And a Nook Gase in my Book Case