Single or multi mode for fiber optic link?

defcon.klaxon · Apr 6, 2020

Hi all,

I have a project where there is a remote control panel that's just a bit outside the range of copper CAT5 so we're going to do fiber optic. I understand there are two modes for fiber optic, single mode and multi mode. From my understanding, single mode is usually used for kilometers long runs where multimode is used for shorter runs. However, when I looked at the specs for a project I worked on a couple years ago (and I didn't have anything to do with the design), I found that we spec'ed single mode and the distance between the two control panels is only ~150 meters, maybe a bit longer due to conduit. After doing some Google searching I really couldn't find a good definitive guide for selecting modes, so I was wondering if anyone here might be able to guide me through which mode to pick, and why? Thank you!

shawn_75 · Apr 6, 2020

Multimode is usually not used in new installations anymore. You won't go wrong if you install singlemode. Be sure to select appropriate equipment with low power levels for your low loss run. You'll likely need attenuators for such a short run.

defcon.klaxon · Apr 6, 2020

shawn_75 said:
Multimode is usually not used in new installations anymore. You won't go wrong if you install singlemode. Be sure to select appropriate equipment with low power levels for your low loss run. You'll likely need attenuators for such a short run.

Thank you for the suggestions!

JaxGTO · Apr 6, 2020

Rockwell/Panduit/Cisco all recommend Multi mode. That is what I am doing at a plant right now using all Stratix switches and a couple of Cisco routers.

Lare · Apr 6, 2020

multi mode is much cheaper

defcon.klaxon · Apr 6, 2020

Well I did some research on the switch that one of the mfr's is providing and it's multimode only, so that's been set.

Now my question is, which OM should I go with?

tragically1969 · Apr 7, 2020

shawn_75 said:
Multimode is usually not used in new installations anymore. You won't go wrong if you install singlemode. Be sure to select appropriate equipment with low power levels for your low loss run. You'll likely need attenuators for such a short run.

Huh ? Multimode is still by far the most common fibre out there, i would use MM without thinking about it.

tragically1969 · Apr 7, 2020

defcon.klaxon said:
well i did some research on the switch that one of the mfr's is providing and it's multimode only, so that's been set.

Now my question is, which om should i go with?

om4

defcon.klaxon · Apr 7, 2020

tragically1969 said:
om4

so my big question is, is a multimode switch able to deal with OM3/OM4 like it's no big deal or do I have to worry about compatibility? Sounds like OM4 provides OM3 bandwidth, but can do it for longer fiber lengths. I'm dealing with less than a kilometer of run so does it matter? All we're dealing with is an Allen Bradley CompactLogix at the remote site sending/receiving data from the main control panel, we're talking about very low data between two PLCs, no internet or anything crazy.

tragically1969 · Apr 7, 2020

defcon.klaxon said:
so my big question is, is a multimode switch able to deal with OM3/OM4 like it's no big deal or do I have to worry about compatibility? Sounds like OM4 provides OM3 bandwidth, but can do it for longer fiber lengths. I'm dealing with less than a kilometer of run so does it matter? All we're dealing with is an Allen Bradley CompactLogix at the remote site sending/receiving data from the main control panel, we're talking about very low data between two PLCs, no internet or anything crazy.

If the switch you have selected is MM then OM1, OM3 or OM4 will work fine, just check the spec of the switch that it will give you a km, for instance the Moxa switches we use state a typical distance of 4km on OM1 (62.5/125) and 5km on OM3, OM4 (50/125)

Charbel · Apr 7, 2020

dear,

Please refer to the below
https://en.wikipedia.org/wiki/Multi-mode_optical_fiber

it given an indication about several type of OM's

I am still using multimode for distances less than 2 km.

Ken Moore · Apr 7, 2020

I would go with OM3 or OM4, both offer gigbit at decent distances if needed. Who knows what you may need in the future. When you pull the fiber, I would pull at least 12 strands, most of the cost is in the labor, so 12 versus 4 strands is minimal.

Lare · Apr 7, 2020

You can even pull fiber which has both SM and MM fibers, even that you need only multimode. Then on future you have allready also SM fibre installed.
Still don't mix different size OM fibres and adapters together.

defcon.klaxon · Apr 7, 2020

Thanks for the help everyone!

Single or multi mode for fiber optic link?

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