Re: [10GMMF] 62MMF connector loss and draft test link config
In the literature
there are many versions of the so called steady state launch mode power
distribution (MPD) or the equilibrium mode power distribution. As far as I
can ascertain the 70/70 launch method is a simple method to approximate the
steady state mode power distribution condition. So on that basis I
believe the calculations are consistent with the 70/70 launch
condition. But I did not specifically model 70/70
information, from the various forms of steady state MPD equations, I used
the one that was simplest for me to add to my calculation. It is the
(1 - N/Nmax) version of Olshanksy:
Olshanky, R (1975).
Applied. Opt. 14: 935-45.
As I said there are
others I could have used but with little real difference in the
RE: 7 or 9
The range of MPD
distributions that could have be used to measure the installed connectors span
the range from OFL to the Steady State. I agree that if Steady State is
assumed then the offset could be as high as 9 um for 0.5 dB loss.
However, the discussion concluded that 9 um did not appear to be a believable
value to use - it's an awfully big offset even for MMF connectors. So, as
I recorded we decided to use the value of 7 um. We also placed two
connectors at the 7 um offset.
The good news is
that we done enough work to narrow the range of offset to (7 to 9)
um. This is quite a small range of values and hopefully we can
formally adopt a value in that range at the next meeting.
I would suggest that
those that have started testing or simulations might be wise to include both 7
um and 9 um as the maximum offset value.
for this work. The model I have for 62.5 agrees with your analysis for
the steady state launch condition. Please confirm that in your model the
steady state condition represents a 70/70 launch (i.e. 70% of maximum core
diameter and 70% of maximum NA).
I have a comment regarding the 7 um limit. The 7 um value was chosen
for the OM3 work because it represented 0.5 dB for 50 um fiber under steady
state conditions. The remaining 0.25 dB needed to reach the 0.75 dB
limit was allotted to mechanisms other than lateral offset. The
equivalent offset for 62 um fiber is 9 um from your graph. Thus
connectors need to be of tighter tolerance for 50 um fiber than for 62 um
fiber. As product lines of cabling vendors in North America and other
parts of the world have shifted to include a larger mix of 50 um fiber, the
tolerance for connectors needed to be tightened to maintain good performance.
Fortunately progress in connector technology permitted this. The
result is that over time connectors have gotten better. This leads to an
interesting issue when dealing with legacy plant. The older plant likely has
poorer connectors due to both tolerance and wear. I think this leads to
a need for considering different values for legacy 50 and 62 um plants.
To address these considerations, I would suggest that the limit for 62
um fiber be set at 9 um and that for 50 set at 7 um.
1300 East Lookout Drive
Richardson, TX 75082
08/18/2004 02:24 PM
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[10GMMF] 62MMF connector loss and draft test link
As promised on todays Fiber Channel Ad Hoc I attach a PDF file
containing the following information:
* My calculated graphs of
connector loss versus offset for overfilled launch, steady state launch and 23
um offset single mode launch.
* The agreed draft of the worst-case test
configuration for channel time variation measurements with comments from our
call to document our reasoning behind the chosen