Re: Corrupted data from SFPs in a single mode system

On Sep 23, 4:38 am, wolahr <w...@xxxxxxxxxx> wrote:
Thanks for the response Phil.  Can you tidy up some loose ends for me,
and make sure I've understood what you've said

Sounds like coherence fluctuation noise due to the back-reflections.
Lasers generally have much worse phase noise than amplitude noise.
Multiple paths with different delays turn the phase noise into amplitude
noise, which can easily be 40 dB worse than the laser's intrinsic
amplitude noise.

So dirt and grease and so on can cause significant enough back
reflections to cause this kind of thing (I understand that you're
saying that although the amplitude of the reflections may seem
harmlessly small, they can phase problem which the real nasty)?

Am I correct to think that even so, most of the signal loss will be
due to absorption of the signal into the dirt, and into the buffer
where it is reflected in silly directions?



In long-haul fibre optic systems it's usually caused by double Rayleigh
scattering, but discrete back-reflections do it too.

Incidentally, is double Rayleigh scattering simply light originating
from Rayleigh scattering being scattered again, and ending up
traveling in the same direction as the original signal?  I say
incidentally because we're only talking about 100m of cable as a
maximum in this system, so I doubt we're dealing long haul issues.





Cheers,

Phil Hobbs- Hide quoted text -

- Show quoted text -

The Rayleigh scattering can be in same or opposite direction.
Direction is rather random really and reflection serves to exagerate
any loss effects. I deal with dirty connections all the time at
contract manufacturer's premises. Contaminents are typically dust or
oils and tend to do just as you say. They'll absorb light like tiny
black (gray?) bodies and rob light amplitude. To extend the analogy
(and risk confuasing everyone again)... these contaminents have been
known to actually burn up and cause disturbing smells and smoke in
land terminal connection wher ouput power is boosted up to some really
high number (a couple watts) of long haul systems.
.

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