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Re: [10GMMF] 62MMF connector loss and draft test link config

RE: 70/70 launch
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 launch. 
For your 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 results.
RE: 7 or 9 um
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.
-----Original Message-----
From: []On Behalf Of Paul Kolesar
Sent: 20 August 2004 04:30
Subject: Re: [10GMMF] 62MMF connector loss and draft test link config

thanks 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.

Paul Kolesar
1300 East Lookout Drive
Richardson, TX 75082
Phone:  972.792.3155
Fax:      972.792.3111

David Cunningham <david_cunningham@AGILENT.COM>
Sent by:

08/18/2004 02:24 PM
Please respond to "IEEE 802.3aq 10GBASE-LRM"

        cc:        (bcc: Paul F Kolesar/CommScope)
        Subject:        [10GMMF] 62MMF connector loss and draft test link config

Dear All,

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 configuration.