Kitz Forum
Broadband Related => Broadband Technology => Topic started by: ColinS on May 27, 2013, 01:56:45 PM
-
see http://www.bbc.co.uk/news/science-environment-22656238 (http://www.bbc.co.uk/news/science-environment-22656238)
Interesting to note that nothing, not even optical fibre, is immune to "noise". :no:
-
Read it earlier, I'm just waiting for OAM. :)
-
Interesting, thanks for sharing Colin :)
But is this new news?
http://jila.colorado.edu/~junye/yelabs/pubs/scienceArticles/1990-1998/sArticle_1994_11_FiberNoiseCancel.pdf
November 1, 1994 /
Delivering the same optical frequency at two places: accurate cancellation of phase noise
introduced by an optical fiber or other time-varying path
By the same Long-ShengMa, as quoted in the BBC item?
-
Interesting, thanks for sharing Colin :)
By the same Long-ShengMa, as quoted in the BBC item?
But is this new news?
Probably not, given your reference, although the guy here is Xiang Liu of Bell Labs
Perhaps the only new 'idea', if it can be called that, is the realisation that the induced noise will be (more-or-less) the same on two fibres in the same cable, and hence will cancel each other out at the receiver by virtue of 'modulating' the two phase-conjugate but otherwise identical optical signals. i.e. an application of the technique by Bell Labs.
This concept, looking back, is quite easy to understand, but surprisingly, nobody did this before
The original paper appears to use a a simple double-pass fiber noise measurement and control system
with an ideal phase locking
and at the time time-delay effects would limit international frequency comparisons via undersea fiber links
i.e. Ideas exist to make use of phase conjugation to "undo" the noise that fibre links add, but they involve adding devices midway along the links' length - sometimes, in the middle of an ocean floor
Whereas What Dr Liu and colleagues instead suggest is creating a pair of phase-conjugate beams, each carrying the same data.
so that At the receiver, if you superimpose the two waves, then all the distortions will magically cancel each other out, so you obtain the original signal back
... a much simpler,more reliable, and less costly approach I would imagine.
The technique seems to be related to the 'phantom' pair idea for VDSL.
-
I'm sure I remember something about this from the last century - or the very early years of this one. Definitely a Chinese mathematician but it was something to do with cryptography and information theory. Something to do with inducing noise into monomode cabling yielding information from "coupled" cabling maybe?
Bugger it, this is going to annoy me until I remember :)