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Dear All, I have attached a presentation which analyzes the connector offset based on the legacy Ethernet and building cabling standards maximum connector loss specifications and worst-case link configurations. Both Ethernet and the building cabling standards limit the maximum per connector loss with overfilled launch (OFL) to 0.75 dB. Furthermore, the worst-case cable model for Gigabit Ethernet is one with two 0.75 dB connectors and, for LX, offset launch jumper cables at each end (in place of normal jumper cables). I have therefore calculated the loss versus offset for 62 MMF with OFL. The allowable worst-case offset is then the offset which produces 0.75 dB of loss - this occurs at approximately 6 um. The main conclusions are: 1) For 62 MMF, if all the loss is attributed to lateral offset, the worst case connector offset is approximately 6 um for a loss of 0.75 dB(OFL). 2) For 62 MMF, the worst case link for modal noise or channel variance measurements is one with two connectors each having 6 um offset equivalent to 0.75 dB (OFL) loss. This is because modal variation effects are larger when there is a small number of higher loss components in the optical path. 3) If three connectors are used the maximum loss (OFL) per connector must be reduced to 0.5 dB which is equivalent to a 4 um lateral offset per connection. Interestingly, if we use the Rayleigh distribution with a mean of 3.58 um, as proposed by Joerg, the probability of a 6 um offset is about 0.1 and the probability of two 6 um offset connectors is about 0.01. If the Rayleigh distribution is correct this means that we are investigating the 1 percentile case which is consistent with the Ethernet methodology. This does not mean that I have confirmed that the proposed distributions of connector offsets is correct - rather I'm just noting that for the 62 MMF case there does seem to be agreement between the two methods on this point. I also have placed the presentation on the FTP site per Jonathan King's e-mail. Regards, David
Worst Connector Offset Calculations.pdf