Using fiber optic for moderate speed data links - Page 1
Forum section: electronics / projects

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 01, 2022, 06:33:52 pm
content: Just a current musing of mine. I'm investigating the benefits and relevance of using fiber optic data links for moderate data throughput - typically in the order of 10Mbps to like 250Mbps, at a reasonable cost. Something simpler and less costly than the typical transceivers used for gigabit+ fiber optic links.So far I've seen TOSLINK - which is already quite old, but variants of it allow up to 125Mbps or 250Mbps from what I've gathered, even though the typical implementation for use in digital audio is under 15Mbps or so. The downside is that there seems to be only one vendor (not surprisingly Toshiba) which sells TOSLINK front-ends, and availability of the higher-speed ones is almost non-existent, even though they are in Toshiba's catalog.So any idea, experience with that, welcome.

author: Marco
author_rank: Super Contributor
timestamp: March 01, 2022, 06:56:31 pm
content: No experience, but aren't the faster solutions mostly from Avago? (Now Broadcomm.)There's also Firecomms.

author: SeanB
author_rank: Super Contributor
timestamp: March 01, 2022, 08:37:41 pm
content: How about fibre adaptors for switches, you can pick up the old ones that are sub gigabit almost for free, and then buy a switch or three to get the matching sockets for them, plus a cheap reasonably good power supply and a case.

author: Hydron
author_rank: Super Contributor
timestamp: March 01, 2022, 09:58:38 pm
content: If you want cheap then SFP(+) fibre modules and sockets (which are 2 parts, SMD edge connector plus a cage to go over it) are probably the best way to go. The Avago/Broadcomm industrial fibre optics stuff is _significantly_ more expensive, and the SFP fibre transceivers will normally work at lower speed than rated (NOT down to DC though, as they are AC coupled - might need to ensure DC balance too).

author: dmendesf
author_rank: Frequent Contributor
timestamp: March 02, 2022, 01:06:36 am
content: Cheap means mass manufactured. Your options here are Toslink and Ethernet.

author: cncjerry
author_rank: Unknown
timestamp: March 02, 2022, 02:48:02 am
content: I put 10Gb in my house and it was dirt cheap. LC-LC cables are really cheap, cards can be had for $20, sfp+ for less than $10, the only thing a little costly is the switch. Go to the networking section of "servethehome.com". Toslink isnt made for data.

author: mjs
author_rank: Regular Contributor
timestamp: March 02, 2022, 08:19:01 am
content: You did not mention what protocols you're using, but gigabit SFP modules can be bought for less than 10€ singles and some types work ok at lower frequencies. Usually not on DC.A hint for using SFPs at low or even DC data rates: use simple FSK tranceiver with differential input/output or balun with some higher carrier frequency for easy SFP connection.Also: BiDi transceivers are mass produced, cheap and you get to run full duplex on single fiber!

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2022, 04:17:49 pm
content: For more reputable supply chains, SFP + socket doesn't seem far off from Avago or Firecomms to me. POF cables are safer to cut to size too.So if simplicity and supply chain factor in, there can still be a case made for the industrial stuff.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 02, 2022, 06:01:22 pm
content: Thanks for the answers so far.I realize my post was not clearly defining the context or applications I had in mind.So, the goal is not to create a network of any kind - there are already perfectly fine solutions these days - but to include an optical data link of some kind for point-to-point communication between devices. I'm mostly interested in the physical interface part, the protocol is already mostly take care of and doesn't have to be anything standard. Also, it would not be just for one-shot projects, but for a more general solution that one could integrate in products.SFP modules would certainly be the easiest path these days. But apart from cost (which admittedly can be mitigated, because yes one can find relatively cheap SFP modules these days, especially in quantities), they are pretty bulky, so anything smaller would be a great plus here.TOSLINK and derivatives are definitely an option, actually. Of course this is a relatively simple solution that works only up to a few meters or a few tens of meters depending on the front-end. But Toshiba has bidirectional front-ends that work up to 250 Mbps up to 20 m, which would actually fit my requirements. Namely, theTODX2402would have been a fit. Unfortunately, it's hard to get ahold of, and the last prices I've seen are not that competitive compared to the cheap SFP modules. So the only benefit here would be size (the TODX2402 is much smaller.) Power draw is also a factor. SFP modules tend to draw signifiant power - but I have not investigated this thoroughly yet.I'll definitely have a closer look at SFP modules and what I can do with them. If anyone has another idea, or knows of SFP modules that are smaller than the typical ones, don't hesitate to chime in.

author: Marco
author_rank: Super Contributor
timestamp: March 02, 2022, 06:27:53 pm
content: It's a transceiver, but it's not bidirectional in the way BiDi SFP is (the TOSLINK transceiver has two fibers).What's wrong with AFBR-59F2Z/AFBR-59F2Z/AFBR-5972EZ/FB2M5LVR/FB2M5LBR/FB2M5KRR/FB2M5KVR?FB2M5KRR/FB2M5KVR are available for $18.56 for singles, which seems competitive if 250 Mbps is enough. The Gbps version is twice that.PS. also you can just jam the cut POF cable into them, simplifies things.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 03, 2022, 02:59:56 am
content: Quote from: Marco on March 02, 2022, 06:27:53 pmIndeed. It's a simple solution, requiring a particular cable and connectors. Actually they even had a TODX2404 for up to 500 Mbps, up to 10 m. Not too shabby. The whole thing was designed for the " Small Multimedia Interface" - but it seems to be pretty much abandoned.Quote from: Marco on March 02, 2022, 06:27:53 pmNothing per se - some mentioned SFP, which I find rather bulky, but that's why I asked if anyone knew of more compact alternatives - so, you answered that.Quote from: Marco on March 02, 2022, 06:27:53 pmYep. But it's still (way) more expensive than any wire-based solution. To be fair though, we would have to factor in the isolation - something that certainly requires extra cost for wired solutions.I also found relatively "compact" (well, they are wider but much less long) and cheap alternatives to SFP, such as the 1x9 bidir SC optical transceivers. I ordered a couple to evaluate this.

author: TC
author_rank: Contributor
timestamp: March 03, 2022, 03:43:24 am
content: Checkout Firecomm Redlink and Optolock. Also MOST... Media oriented system transport.General search terms are pof plastic optical fiber transceiver.Others have replied with related products.

author: Renate
author_rank: Super Contributor
timestamp: March 03, 2022, 11:37:39 am
content: I was looking at this stuff for even lower speeds and it still seems like you are talking ~$10 for a transceiver.I used to have some of that 1mm plastic "cut it with a knife" stuff. It's still around, but as I said, ~$10.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 03, 2022, 05:50:08 pm
content: Quote from: Renate on March 03, 2022, 11:37:39 amI suppose you're talking about the cheap plastic connectors containing either a LED or a photodiode (so unidirectional), and for use with cheap plastic fiber?Like this?https://www.digikey.fr/en/products/detail/industrial-fiber-optics/IF-E91A/243775They used to be a bit cheaper than this, but they're still there and affordable. For low-speed stuff (probably to be used for max 1Mbps or so), that should do it. Of course that's unidirectional, so if you need bidirectional communication, that requires two connectors and two cables, which becomes clunky.Edit: this onehttps://www.digikey.fr/en/products/detail/industrial-fiber-optics/IF-E91D/389820is claimed to be good for up to 100Mbps up to 10m, so that's certainly a cheap option if unidirectional is OK.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 03, 2022, 05:58:29 pm
content: Quote from: TC on March 03, 2022, 03:43:24 amThanks about that, I had a look and those are a definite option from a technical standpoint. Have no clue about pricing though. They are apparently not distributed through the usual distributors and I'll need to contact sales to get an idea of the pricing...Quote from: TC on March 03, 2022, 03:43:24 amYeah, as I mentioned: TOSLINK and SMI. While TOSLINK is still there, but rumored to become obsoloted, SMI has disappeared. Do you know of any other kind of optical "media-oriented" system (other than the now standard SFP stuff?)

author: Renate
author_rank: Super Contributor
timestamp: March 03, 2022, 06:44:51 pm
content: What is the cheapest bi-directional (half duplex) out there?

author: Nominal Animal
author_rank: Super Contributor
timestamp: March 03, 2022, 07:19:59 pm
content: TME has cheap Cliff TOSLINK transmitters and receivers in the 2-6€ range in singles, with max. 16 MBit/s bandwidth using NRZ. Only need a couple of bypass caps per transmitter and receiver.I've played with (logic-inverted) UART via TOSLINK –– that is, a pair of TOSLINK cables for a bidirectional link –– a few years ago. IIRC, I used 2 Mbaud (8n1) between two Teensies at 3.3V.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 04, 2022, 05:46:37 pm
content: Quote from: Renate on March 03, 2022, 06:44:51 pmI suppose you mean single-fiber?Define "cheap". As I mentioned, I found 1.25Gbps bidir modules for about $10 a pair, which I consider cheap. Those are not SFP, but with relatively similar characteristics.The downside is the size - while not quite as long as SFP modules, they are wider and still pretty "chunky".https://www.aliexpress.com/item/4000423193534.htmlI've taken a look at Firecomm Redlink and Optolock stuff though. Not seen all the offering yet, but maybe there's something there that would fit.

author: Marco
author_rank: Super Contributor
timestamp: March 04, 2022, 10:49:35 pm
content: Also likely they are here today, gone tomorrow.