Do mechanical splices have more reflectance? On Fri, Aug 22, 2025 at 5:47 AM Adam Moffett <[email protected]> wrote:
> Well, I couldn't let it go. It dawned on me this morning why -32dB > optical return loss figure actually matters. The OLT will get reflections > from every output leg of every splitter. Start adding all of that up and > you can start to approach the specified limits of total optical return > loss. > > The logarithmic scales aren't always intuitive. One bad value can hurt > really bad. In this example, my one "Bad connector" with -40 reflectance > has the impact of adding roughly 300 SC-APC connectors. > > > ------------------------------ > *From:* Adam Moffett <[email protected]> > *Sent:* Thursday, August 21, 2025 5:34 PM > *To:* AnimalFarm Microwave Users Group <[email protected]> > *Subject:* Re: [AFMUG] Help me Grok this - tolerance to reflected power > > I think I figured out the limits.....or a limit. > > ITU G.9807 is saying that the minimum optical return loss for > 10Gig operation is 32dB. > Return loss is the opposite of reflectance. -65dB reflectance = 65dB > return loss. You sum the power of all the reflections to get the total > optical return loss on the path. A simple way is every time you double the > number of connectors you get another 3dB of reflectance (better formulas > exist of course). > > If I have 8 of those -65dB APC connectors then my total ORL (all else > being perfect) is 56dB. It would take a whole lot of good connectors to > get you to 32dB ORL. Or one really bad connector. I suppose the twist-ons > aren't a big problem as long as they're done decently. > > Technically Raleigh scattering also adds to the total ORL, but it's > negligible compared to the connectors. > > -Adam > > > > ------------------------------ > *From:* AF <[email protected]> on behalf of Mark Radabaugh < > [email protected]> > *Sent:* Thursday, August 21, 2025 1:15 PM > *To:* AnimalFarm Microwave Users Group <[email protected]> > *Subject:* Re: [AFMUG] Help me Grok this - tolerance to reflected power > > It’s not much of an issue on PON as far as I can tell. If you are > running RFOG (analog cable added to the fiber) I think it’s a much bigger > issue. I don’t know of very many companies still running RFOG. > > Mark > > On Aug 21, 2025, at 1:00 PM, Adam Moffett <[email protected]> wrote: > > I think the "tolerance to reflected power" was the wrong direction to > look. That seems like it's more about not damaging the equipment. I'll > back out of the rabbit hole and just ask what I'm trying to figure out: > > How much does reflectance actually hurt you on PON? Google results are > vague. > > Example: You generally need to have two connectors at the OLT (device to > patch panel), and there's one connector at the ONT. If you fusion spliced > everything else so there were no additional reflective events, would there > be a measurable BER or stability difference compared to having a coupler in > the NID, connectorized splitters in the field, etc. > > Another example: An AFL Fastconnect twist-on SC/APC field termination has > -50dB reflectance according to the spec sheet. A factory terminated > connector or splice-on connector is -65dB. How much does the twist-on hurt > you? > > > -Adam > > > ------------------------------ > *From:* Adam Moffett <[email protected]> > *Sent:* Thursday, August 21, 2025 11:54 AM > *To:* AnimalFarm Microwave Users Group <[email protected]> > *Subject:* Help me Grok this - tolerance to reflected power > > > Definition from ITU G.987: > 3.3.15 tolerance to reflected power (transmitter): A transmitter parameter > that characterizes the > maximum admissible ratio of the average reflected optical transmit power > incident at the transmitter > to the average optical transmit power. > > If my average transmit power is +6dBm and the tolerance to reflected power > is -15dB, then 6 - 15 = -9, so reflected power as strong as -9dBm won't > harm the transmitter? > Is it that easy or am I misunderstanding the definition? > > -Adam > > > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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