Range using single-mode SFPs across multi-mode fiber

Jeff Kell jeff-kell at utc.edu
Wed Dec 14 20:50:47 UTC 2011

On 12/14/2011 3:37 PM, Keegan Holley wrote:

> Single mode just has a smaller core size for the smaller "beam" emitted by
> laser vs. LED.  it works although I've never done it outside of a lab (MM
> is cheaper). As for the distance it theory that should come down to the
> optics and your transmit power.  Hopefully this is just a cable connecting
> the router to a long line.  I've never heard of a 10K MM fiber run since SX
> optics can't shoot that far.  You should be able to get through the 500m or
> so that MM optics are rated for, but YMMV (errors, light levels, bounces,
> etc etc)

Cisco gives specs for SFP LX over MM (they aren't that great at gig, and really suck at
10G; if you have 50u OM3/OM4 you can do much better at 10G).

See SFP/fiber/distance table at

We have run LX-over-MM (62.5) on short building runs as a band-aid until SM is
available, and trying to do all new building MM with 50u OM3/OM4.  We do have some
dependence on 62.5u MM - used by our aging Simplex alarm system - which does
point-to-point looped token ring <*cough*> on the alarm side.  I'm trying to get them to
confirm 50u will work point-to-point, but at some non-alarm-points there would be a
necessary 50-to-62.5 exchange taking place and I'm not certain how to accomplish that
(50->62.5 would likely have tolerable loss, but not 62.5->50).

(I would suspect similar results cross-vendor but YMMV)


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