Solved: Connecting a 100 Base FX transceiver to single mode fiber

George Karimi · ‎11-14-2014

I'm looking to connect to an ISP circuit. The fiber run is single mode and they have a 100 Base FX transceiver on their end.

I've looked up the specifications on that transceiver and it say's it should only be run on SMF.

Anyone had any success with this?

Marvin Rhoads · ‎11-14-2014

You're welcome.

For a VERY short run your MIGHT be able to get a SM transceiver to work over MM fiber.

The coherent light ("single mode") from the laser that launches into much larger core of the multimode fiber (usually 50 or 62.5 microns vs 9 micron for SM and having different propagation and dispersion characteristics) may "punch through" over short distances.

I wouldn't do it in any production environment though as it would likely be unstable in the long term (and is definitely not how the equipment is designed to work).

View solution in original post

Marvin Rhoads · ‎11-14-2014

The 100BASE-FX is designed for and only works with multimode fiber. This is noted in the product data sheet.

The singlemode variants of the product line are listed on the same data sheet.

Whatever variation is being used should match at both ends and use the proper fiber (MM or SM).

George Karimi · ‎11-14-2014

thank you for your response Marvin.

I'm just wondering if anyone has actually tried this. The ISP i'm working with claims that it works on both, though I highly doubt it.

Marvin Rhoads · ‎11-14-2014

You're welcome.

For a VERY short run your MIGHT be able to get a SM transceiver to work over MM fiber.

The coherent light ("single mode") from the laser that launches into much larger core of the multimode fiber (usually 50 or 62.5 microns vs 9 micron for SM and having different propagation and dispersion characteristics) may "punch through" over short distances.

I wouldn't do it in any production environment though as it would likely be unstable in the long term (and is definitely not how the equipment is designed to work).

George Karimi · ‎11-14-2014

Understood.. thanks again.

dcioffi · ‎09-02-2016

Hello George,

I know you posted this question two years ago but I have a provider now that's doing the same thing: They're using a 100Base-FX SFP over singlemode fiber. Like you, we're thinking this shouldn't work.

Did you try it? And did it work?

jack.scuba@gmail.com · ‎03-07-2019

I have a situation similar to George's

The tower supplier suggested MOXA EDS-308-SS-SC-T.

I get that you might get a SM transceiver to work over a MM Fiber for a short distance but that does not apply to this situation. Here we have an optical Standard 100FX from another Vendor (MOXA) that claims to work over SM Fiber. In my case this switch is paired with a SM Fiber. What I'm looking for is a CISCO Transceiver that will Work with the MOXA Optical Standard 100FX over SM Fiber. I've provided a link to their Switch's page.