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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    – Ron Maupin
    Dec 16 '20 at 23:48

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.


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.

  • The 'M' in -LRM stands for multi-mode - the L indicates Long wavelength (1300 nm).
    – Zac67
    Nov 25 '19 at 21:52
  • 1
    @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
    Nov 25 '19 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
    Nov 25 '19 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
    Nov 26 '19 at 16:35
  • 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
    Nov 4 '20 at 10:29

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.

  • SMF may be more expensive to terminate but the actual fiber is cheaper than MMF.
    – Zac67
    Nov 4 '20 at 10:25

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