Troubleshooting Fiber Optic.

uptown47 said:

Just as a side note... I did a fibre installation course many many moons ago (about 25 years ago) and I remember that the Optical Time Domain Reflectometer (OTDR) used to use a principle called Fresnell Reflection in order to determine where the break/bad bend is in a fibre.

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You got a good memory, uptown.

So, because the speed of light is a constant, the OTDR fires light down the fibre.

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Going to pedantic for a moment. The speed of light in vacuum is a constant. Speed of light in fiber is not. It depends on the construction of the fiber and wavelength of light. Typical index of refraction in a fiber is about 1.45, so the speed of light in a fiber is only about 2/3 of the speed of light in vacuum. Knowing the index of refraction is important to be able to use an OTDR accurately.

Bit_Bucket_07 said:

I wouldn't make that kind of an investment simply for maintaining on-site fiber optic cables. It would make sense for someone who intends to do fiber optic installations on a regular basis. I suppose it would also make sense for maintenance personnel who work for companies that have unlimited budgets.

A simple laser is usually sufficient for basic troubleshooting.

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I agree completely. My facility has about a dozen fiber runs, 50% for IT and 50% for industrial. We keep basic tools on hand for troubleshooting and cleaning, but for deeper issues we use a contractor that has the tools and training to handle it.

Timbert said:

You got a good memory, uptown.

Going to pedantic for a moment. The speed of light in vacuum is a constant. Speed of light in fiber is not. It depends on the construction of the fiber and wavelength of light. Typical index of refraction in a fiber is about 1.45, so the speed of light in a fiber is only about 2/3 of the speed of light in vacuum. Knowing the index of refraction is important to be able to use an OTDR accurately.

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Yes!! I remember that now. I used to really like working with fibre. Spending ages stripping an outdoor cable down to it's bare fibre. Peeling off layers of anti-rodent poison on brown paper and cutting through wire armour to work your way down to just the tiniest strand of glass. Amazing stuff!

And the disappointment of flashing a joint and then looking through the microscope to see that one side had cracked or the joint had bulged and didn't look good. But the thrill of getting the joint absolutely bang on!

Great stuff!

My money is on a bad fiber converter. I find that the fiber is rarely the problem.

1. Look up the specs on the old vs the new converters. Make sure the fiber side specs are the same.

2. Aqua colored patch cables are a bit of a specialty thing. I commonly see orange patch cables for multimode.

3. If your original converters were working and now the new ones are not, that points to a mismatch between the old and new. Could be the laser type, the new pair isn't a match on each end, wrong fiber type, etc...

4. You may need to swap fibers AT ONE END ONLY. You may have the Tx laser pointed to the Tx laser on the other converter.

I wouldn't bother with a specialty tester at this point.

This is multimode, so get someone to blink a regular flashlight into each strand of the installed fiber one at a time. This will allow you to ensure that strand 1 matches strand 1, strand 2 matches strand 2, etc... as marked on both ends.

I once encountered a relatively short, multimode fiber optic link that wouldn't work because the signal was too strong, oversaturating the receiver. We had to tie a few loose knots into the fiber to attenuate the signal. There are probably attenuators designed specifically for that purpose, but the knots did the trick. I think it was on a RIO link for a PLC-5.

I know this thread is a few days old, but I wanted to let everyone know what the problem was.

I time and cleaned all connections with alcohol and, everything started working. I almost gave up at first. Every connection that I cleaned looked new. I was amazed when it started working. Im grateful though.

I wanted to thank everyone for their help with this problem.

HoldenC said:

I know this thread is a few days old, but I wanted to let everyone know what the problem was.

I time and cleaned all connections with alcohol and, everything started working. I almost gave up at first. Every connection that I cleaned looked new. I was amazed when it started working. Im grateful though.

I wanted to thank everyone for their help with this problem.

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Thanks for the follow up. I was involved in a rather large fiber optic installation several years ago, and upon testing, we encountered one particular link with very high loss. This link passed through numerous splice cabinets. We eventually discovered the culprit. While inspecting one of the connectors with a microscope, there was a tiny speck of green cladding that had landed precisely over the fiber core. Wiped it with a swab, reinserted it, and we were good to go.