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if one has a run of singlemode fiber terminated in a patch panel, how would you then connect it over to a device? singlemode patch? it was my understanding that singlemode had minimum refraction distance requirements.

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4 Answers 4

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With singlemode patch cables

http://www.lanshack.com/Singlemode-Fiber-Optic-Patch-Cables--C17.aspx

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Nunya is right, but you should also try to match your fibre patches to the existing patches - for instance there are a lot of different types of single-mode, read the details from the side of the existing fibre and try to match that ok. –  Chopper3 Jan 27 '10 at 8:38

I'm not a fiber expert, so take this for what it's worth: I support a campus network w/ 3 single mode gigabit Ethernet links to remote buildings. In the closets the fibers are patched with 1 meter single mode patch cables. They all work fine.

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I've never had a problem with refraction on single mode.

Here's some more related details:

Minimum lengths should only matter on high power interfaces.

With fiber you've got a Transmit path and a Receive path.

If you bought a very expensive port that transmitted on a power level that was higher than the maximum receive tolerance of your receive port, you could potentially 'burn out' the receive optics.

For example, take a look at this list of Cisco Gigabit Ethernet SFPs.

http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html

The 1000BASE-LX module (10,000ft over singlemode) is safe on short cables because the hottest it can transmit is -3db, and the hottest it can receive is -3db (same tolerance).

The higher power 1000BASE-ZX module (up to 70km over singlemode) can transmit at +5 db, but has a receive maximum of -3db. If you used a short cable to connect that directly to itself, you would likely burn out the receiver.

To be safe, fiber techs normally use fiber 'pads', which are just filters to lower the strength of a signal.

You can also get a fiber light meter from a company like Noyes. That will show you the strength of the signal at that patch.

Another rule of thumb is that most patches give you 2 to 3 db of loss. (depending on the quality of the work.)

I hope this helps.

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I've never heard of a minimum length of single-mode fiber, and since the "single mode" that's referred to means that the light travels straight along the fiber without internally reflecting, I don't think there could be one.

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Reflections wouldn't be the issue, just plain old signal strength. The longer the fiber (and the more connections/splices) the dimmer the light at the other end. A high-power transmitter can overload a sensitive receiver if there's not enough "dimming" (attenuation) between them. –  Paul Apr 27 '10 at 19:53

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