optical loss per mile

Unanswered Question
May 21st, 2008

I would like to try and figure out how to find my real world optical loss per mile.


In a recent install I did my OTDR distance read about 79,200 feet. My CWDM starting optical power was +2.62 and my ending was -4.51. So is my optical loss per mile -.48?


I just want to make sure my formulas are all correct so that I can predict things a little better.


Thanks!

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Tom Randstrom Thu, 05/22/2008 - 05:24

Typical fiber loss for singlemode fiber at 1550nm is 0.25dB/km.


79,200 feet = 24.2 km

24.2 km * 0.25dB/km = 6.5dB fiber loss


Estimated 15 splices at 0.06dB each (fusion splice) = 0.9dB


Your link loss was 7.13dB, so it looks like your link is performing within an acceptable range.


Make sure you document your links so you know your starting point when troubleshooting system issues in the future.


Hope this helps.


Tom



sjamison76 Fri, 05/23/2008 - 07:06

Thanks Tom! I am really new to figuring out all this optical loss stuff, and Im trying to get my head around it.


I didnt get the OTDR reading because the Aerial MUX I put in killed the OTDR because it couldnt pass that 1550 wavelength when I was doing 1470/1490 through it. So we read it from one direction to the passive, and then from the other direction to the passive then came up with how many feet.


So my next dumb question is, if Im taking the power readings at both ends after everything is installed with the laser up, wont the optical power meter be taking in account of all the loss already from the fusion splices and passives?


Im trying to just get some real world values, rather than try and say ya the lasers are good for 70km, when maybe I could do farther (or shorter) than that based off what Im seeing from the installs I do. (Since the OTDRs we have cant pass through those passive MUX's at those wavelengths.)


Thanks!

Tom Randstrom Fri, 05/23/2008 - 08:34

"So my next dumb question is, if Im taking the power readings at both ends after everything is installed with the laser up, wont the optical power meter be taking in account of all the loss already from the fusion splices and passives?"


If you are measuring the performance using a power meter, the reading on the meter will be inclusive of all losses on the link, including fiber, muxes/demuxes, splices, connectors, and bend induced losses. This type of testing confirms the actual received signal level and allows you to understand if the link is operating within the expected range. Again, it is good to document the power readings for future troubleshooting.


Hope this helps!

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