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fiber optic

fiber optic

Hi all,
the OTDR testing of 14km fiber optic shows attenuation -0.174 dB,it my first time seeing negative attenuation,please help to interpret this value knowing that the acceptance criteria is 0.1 dB as per specification.

RE: fiber optic

People get funny with decibels (dB). To make 10 dB of attenuation sound worse than 0.1 dB of attenuation they put a negative sign in front of it. That gets confusing, because theoretically -0.174 dB of attenuation is the same as 0.174 dB of gain (if your fiber is designed to be non-linear it might give you gain). It also gets based on perspective, as in if attenuation is a good thing (something you are designing for) or a bad thing (something real you need to overcome).

All that said, if your spec is 0.100 dB of attenuation, it looks like you are failing by 0.074 dB. That isn't much; is your OTDR tester properly calibrated?


RE: fiber optic

thx zappedagain for your reply.
I confirm,our tester is properly calibrated.
warm regards

RE: fiber optic

Generally, fiber optic cable has no gain, being purely passive. However, there are certain wavelengths that might excite non-linear behavior, such as 2nd harmonic generation.

What material is the fiber?
What wavelength is the OTDR using?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
FAQ731-376: Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list

RE: fiber optic

thanks for reply.
1550 nm and 1330 nm for wavelength.

RE: fiber optic

So, negative attenuation is essentially gain, but it's unlikely that you actually have gain, so there may be a coupling error somewhere in the path.

How does the system actually do the measurement, i.e., what is it comparing against to determine attenuation? I'm thinking that there's a measurement with and one without the cable, and the system takes the difference to be the attenuation.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
FAQ731-376: Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list

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