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I just started working with new company and found they are using SFP-10G-LRM with single mode fiber. How could this be? I thought since the SFP-10G-LRM is Multimode, it can't work with single mode fiber. apparently I'm missing something here.

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin ♦
    Commented Dec 16, 2020 at 23:48

4 Answers 4

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It can use multimode, but it doesn't have to:

The Cisco 10GBASE-LRM Module also supports link lengths of 300m on standard Single-Mode Fiber (SMF, G.652).

From the data sheet.

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  • Not all -LRM modules work well with SMF. It depends on their design.
    – Zac67 ♦
    Commented Apr 21, 2022 at 6:29
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If you use the Cisco utility to search for transceiver compatibility on a router/switch model with SFP+ ports, it WILL list the -LRM part twice.

XcverProdID Reach Media

SFP-10G-LRM 220m MMF

SFP-10G-LRM 300m SMF

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  • Please do not ask questions in an answer. Start a new question to ask a question.
    – Ron Maupin ♦
    Commented Apr 21, 2022 at 1:14
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Generally speaking, any transceiver type that begins with "L" (for example: LR, LX, or LH) are designed to get their best range over SM fiber.

In some cases they may also be used on MM fiber, typically with reduced ranges. They may also require a mode conditioning patch cable to do so properly. You should check the respective data sheet for the transceiver to verify if it can be used on MM fiber and if it requires a mode conditioning patch cable.

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  • The 'M' in -LRM stands for multi-mode - the L indicates Long wavelength (1300 nm).
    – Zac67 ♦
    Commented Nov 25, 2019 at 21:52
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    @Zac67, it is the variation of LR that operates with both SM and MM. IIRC, the other 109G one that operates with both is LX4. Doesn't change the facts that just like any of the other "L" mediums that can operate on both, it has better range characteristics on SM and may require the use of line conditioning patch cords to operate properly on MM.
    – YLearn
    Commented Nov 25, 2019 at 21:57
  • Check IEEE 802.3 clause 68 - officially, LRM is intended for MMF only. Of course, it's possible to use it on "short" SMF runs as well.
    – Zac67 ♦
    Commented Nov 25, 2019 at 22:09
  • So If LRM is intended for MMF only, then it would be better to change all SMF to MMF then?
    – A Culver
    Commented Nov 26, 2019 at 16:35
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    By IEEE standard, -LRM is only suited for MMF (see Clause 68.5 PMD to MDI optical specifications) - however, many actual products do support SMF, check their spec sheet. SMF will likely work anyway but the achievable reach can vary extremely, depending on the laser type and coupling method within the transceiver.
    – Zac67 ♦
    Commented Nov 4, 2020 at 10:29
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Yes, it can and the transmission distance can be little longer, as single mode fiber is expensive and higher performance than that of multimode one.

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  • SMF may be more expensive to terminate but the actual fiber is cheaper than MMF.
    – Zac67 ♦
    Commented Nov 4, 2020 at 10:25

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