Testing Fibers

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Stril

Member
Sep 26, 2017
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Hi!

Currently, I have a lot of problems with my fibers (MMF and SMF). The fibers have been installed by a local company some years ago, but some of them do not operate on 10GbE, some also not on 1GbE.


To cut a long story short:
I want to be able to verify the fibers, if they have damages or if they are not installed properly.

Can you recommend me a setup <5000$ to do this?

My first try was:
2x Mikrotik-router with SFP+-Modules
--> Shows up input/output-level
--> Can REALLY show, if 10GbE is possible
--> does not show length or details about problem
--> not very handy


Second idea:
Simple Optical Power Meter
--> Easy to use
-->handy
--> very unprecise


Third idea:
OTDR
--> Too expensive...

Thank you for your help!

Regards,
Phil
 

Terry Kennedy

Well-Known Member
Jun 25, 2015
1,140
594
113
New York City
www.glaver.org
Currently, I have a lot of problems with my fibers (MMF and SMF). The fibers have been installed by a local company some years ago, but some of them do not operate on 10GbE, some also not on 1GbE.

To cut a long story short:
I want to be able to verify the fibers, if they have damages or if they are not installed properly.
Are these fibers within a room, within a building, within a city, or...? That makes a great deal of difference as to how they would be tested.

If these runs have splices in them (typical on longer runs), furnishing OTDR plots is pretty much standard as part of the installation. Did you receive copies of those when your fibers were originally run?

Since you mention MMF, I would assume that those are relatively short runs, likely within a single building. If these are the older 62.5/125 fiber (orange jacket) you need to use mode-conditioning cables at each end for reliable 1GbE operation.

You won't get a good answer simply using router / switch ports with SFP/SFP+ modules. That only shows if the link will work (or won't) at the present time and doesn't tell you anything about margins.

The optical power meter should give you accurate loss readings, assuming your meter operates at the wavelength(s) that you plan on using on the fiber. Simply plugging a unit onto each end of the fiber isn't sufficient, though - you should connect the transmitter and receiver using known lengths (10' is good) and a coupler, of the same type of fiber you are using for the actual run on each end, and measure the loss. Now connect the transmitter and receiver to the fiber you want to test. The difference between the reading you get from that and the reading you got when connecting the units together with the 10' launch cables is the link loss in your fiber under test. In difficult situations, you may want to swap the transmitter and receiver. Asymmetric loss is unusual, but it can happen.

For longer runs you are going to need an OTDR. You don't have to buy one, though - you can ask the company that originally installed your fiber to run the tests for you, or you can contact a different company. Sometimes a company will do the OTDR scans at a reduced price (or even free) if they think you will use them to repair / replace any defective fiber. This depends on where you are, though - you'll likely find more companies in New York, NY than you will in a less-populous city.

Here is a sample OTDR report from a long (150,000-foot) fiber with many splices: