No Subject

["Dave Emery" <die@pig.die.com>]

> 
> Bob writes:
> 
> > Does anyone know if the new in-line optical amplifiers (not switches!) have
> > any effect on quantum crypto messages?

  Optical
> repeaters have to pass your signal through an intermediate electronic
> stage anyway, since we have no purely optical valve/transistor
> equivalents (bosons don't interact with each other at all).

	This is not true.   There is now a whole technology of optical
amplifiers for fiber communications systems that used Ettrium doped
fibers pumped with strong light from a laser at a slightly shorter
wavelength. These fiber optical amplifiers have gains in the order of
10-12 db in a section of special doped fiber only about 10 feet long.

	The current generation of undersea cables from the US to Europe
use these amplifiers instead of the more traditional regenerating
repeaters that convert the light to electronic signals, reclock the data
stream and convert it back to light with another laser diode.   There is
no conversion from light to digital electronic signals all the way from
Rhode Island to England - the same light pulses that go into the fiber
on one side of the Atlantic come out on the other end without ever
having been converted to electronic form in between.

	 These amplfiers have enourmous bandwidth, and can be used to
amplify several slightly different wavelengths of light allowing
wavelength division multiplexing of multiple streams of light flashes of
slightly different "colors" (all the current technology works at around
1500 nm which is well into the infrared).   This can expand the capacity
of a single fiber to four to six times the 5 Gb/sec that is the current
state of the art.

							Dave Emery
							die@die.com


























                                        

> 
> Can someone think of a reason why this wouldn't necessarily be so?
> 
> > Cheers,
> > Bob Hettinga
> 
> - alex
>