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I'm looking for a way to convert UART data to multimode fiber. I've seen a few examples of single mode conversions, but that won't fit the application. Has anyone ever done this? I know that most SFP rated for at least 10MB transmission (minimum) requires differential signal connection, but I'm uncertain of the requirements for those devices. Hoping someone here has done it before. I can't buy a converter module either, it won't fit where this is going.

Jedi Engineer
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    Should be straightforward to hook up TOSLINK to almost anything if you only need megabit/s data rates. – user1850479 Jun 25 '21 at 00:26
  • As far as I am aware, the lowest speed supported by SFP modules is 1 Gbps. What data rate and distance do you actually need? – The Photon Jun 25 '21 at 00:54
  • https://www.amazon.com/UT-2077-Self-powered-RS-232-Optical-Fiber/dp/B00GI9GM68 – Chengxian Zhang Jun 25 '21 at 01:13
  • @Thephoton I happen to know people that have done the 10 MHz reference clock distribution in their home with SFP adapters directly attached to the clock source. See also hardware like http://osmocom.org/projects/misc-hardware/wiki/Sfp-experimenter – mmmm Jun 25 '21 at 07:23
  • Avago (nee HP) have some pcb modules that take ttl in/out to fiber. As mentioned, Toslink is a cheap alternative if you’re only doing short distances. – Kartman Jun 25 '21 at 09:20
  • @mmmm, 10 MHz is almost certain to work, because there is very high transition density. Even 10 Mbps data, with reasonable encoding like Manchester or even 8b/10b, is highly likely to work (but not guaranteed). 1 Mbps data without encoding, or 10 kbps data is pretty likely to cause problems (but YMMV, depending on the SFP vendor, blah blah blah). – The Photon Jun 25 '21 at 15:55
  • @Kartman, Avago is now called "Broadcom" although I think they do still use Avago branding for those products. – The Photon Jun 25 '21 at 15:58
  • @user1850479 Thanks, but can I use it over 1km distance? RS485 is good to 4000ft, but I can't use copper in this instance. – Jedi Engineer Jun 25 '21 at 23:57
  • @ThePhoton SFP is differential, running at 125MHz, not sure about the lower end though. I know the lowest TYPICALLY used with SFP is 10Mbps, but that's it.. – Jedi Engineer Jun 25 '21 at 23:58
  • @thePhoton good point! So, 10 MHz continuous carrier plus the data as say 16 MHz on-off-keying on top? – mmmm Jun 26 '21 at 00:34
  • Assuming you pick low loss MM fiber I think you could have almost arbitrarily long links with most protocols. At least at kilometer distances the delay is probably short enough that anything used with a UART is unlikely to care. – user1850479 Jun 26 '21 at 13:58

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