Any COMPELLING reason to opt for single multimode fiber, instead? I'm only looking at a few hundred feet run. (the dual fiber solution is "free" for me)
Single mode, dual fiber optical link downsides
Started by ●September 22, 2020
Reply by ●September 22, 20202020-09-22
On Tue, 22 Sep 2020 11:52:01 -0700, Don Y <blockedofcourse@foo.invalid> wrote:>Any COMPELLING reason to opt for single multimode fiber, instead? >I'm only looking at a few hundred feet run. > >(the dual fiber solution is "free" for me)I'm about to get my first articles of a duplex fiber link, ECL in and out at maybe 1M to 2 GHz. It's for testing missiles or something. I'm using a Cisco 10G 850nm multimode SFP module, which is probably good for a few hundred meters at my speed. It will run through several gymbal joints that have "fiberoptic slip rings" What's strange is that Amazon wants about $20 for the SFP. Digikey wants $94. The list price is $1200. How fast do you plan to go? Need DC coupling?
Reply by ●September 22, 20202020-09-22
On 9/22/20 12:52 PM, Don Y wrote:> Any COMPELLING reason to opt for single multimode fiber, instead? > I'm only looking at a few hundred feet run. > > (the dual fiber solution is "free" for me)I would strongly advocate for dual fibers (one in each direction) unless you have a specific reason to not use dual fibers. Single fiber usually means that you need Bi-Directional optics which are more rare and more expensive. They also transmit and receive on different wavelengths. So sparing parts is more complicated because the ends aren't like for like. -- Grant. . . . unix || die
Reply by ●September 22, 20202020-09-22
On Tuesday, 22 September 2020 20:47:28 UTC+1, John Larkin wrote:> On Tue, 22 Sep 2020 11:52:01 -0700, Don Y > <blockedofcourse@foo.invalid> wrote: > > >Any COMPELLING reason to opt for single multimode fiber, instead? > >I'm only looking at a few hundred feet run. > > > >(the dual fiber solution is "free" for me) > > I'm about to get my first articles of a duplex fiber link, ECL in and > out at maybe 1M to 2 GHz. It's for testing missiles or something. > > I'm using a Cisco 10G 850nm multimode SFP module, which is probably > good for a few hundred meters at my speed. It will run through several > gymbal joints that have "fiberoptic slip rings" > > What's strange is that Amazon wants about $20 for the SFP. Digikey > wants $94. The list price is $1200. > > How fast do you plan to go? Need DC coupling?I bought four of those a few years ago on eBay for about $10 in total. Hardly anyone uses 850nm multi-mode anymore which is why they are so cheap. Single mode fibre is now usually cheaper than multimode. John
Reply by ●September 22, 20202020-09-22
On 9/22/2020 12:47 PM, Grant Taylor wrote:> On 9/22/20 12:52 PM, Don Y wrote: >> Any COMPELLING reason to opt for single multimode fiber, instead? >> I'm only looking at a few hundred feet run. >> >> (the dual fiber solution is "free" for me) > > I would strongly advocate for dual fibers (one in each direction) unless you > have a specific reason to not use dual fibers.That was, essentially, the question: IS there any reason to avoid the dual single-mode solution? Yeah, it "looks" a bit more dated...> Single fiber usually means that you need Bi-Directional optics which are more > rare and more expensive. They also transmit and receive on different > wavelengths. So sparing parts is more complicated because the ends aren't like > for like.Good point! I can probably dredge up the necessary SFPs, etc. but I only have dual, single-mode fiber available to me, presently, so that's the most straight-forward solution...
Reply by ●September 22, 20202020-09-22
On 9/22/20 4:14 PM, jrwalliker@gmail.com wrote:> Hardly anyone uses 850nm multi-mode anymore which is why they are > so cheap.I see multi-mode / 850 nm / short reach used all the time, including new installations. I've seen a LOT of Fibre Channel make *HEAVY* use of 850 nm. It all has to do with the distance that you need to go. 850 nm / multi-mode / short reach is almost always cheaper and earlier to appear than single-mode counterparts at faster and faster speeds. If you need something to go from a switch to equipment in the same cabinet / row / moderate sized data center, then 850 nm / multi-mode / short reach is a perfectly viable candidate. I've done some 100 Gbps over multi-mode within the last few months. -- Grant. . . . unix || die
Reply by ●September 22, 20202020-09-22
On 9/22/20 5:18 PM, Don Y wrote:> That was, essentially, the question: IS there any reason to avoid > the dual single-mode solution?In my personal, and professional opinion. Nope. Not at all. Duplex (separate fiber in each direction) single mode works perfectly fine. I've installed a lot of it in the last few months.> Yeah, it "looks" a bit more dated...So. I don't mind being blunt here. IPv4 (and v6) is also dated. Yet almost all of us are doing new deployments or expansions with it every single day. I believe that Steve has said something to the effect of "just because something is old does not mean that it has a problem".> Good point! I can probably dredge up the necessary SFPs, etc. but > I only have dual, single-mode fiber available to me, presently, > so that's the most straight-forward solution...If you have dual single mode fiber, you also have two single strand single mode fiber too. ;-) Use what you have. Worry about changing it later if it ever becomes a problem. -- Grant. . . . unix || die
Reply by ●September 22, 20202020-09-22
On Tue, 22 Sep 2020 15:14:18 -0700 (PDT), jrwalliker@gmail.com wrote:>On Tuesday, 22 September 2020 20:47:28 UTC+1, John Larkin wrote: >> On Tue, 22 Sep 2020 11:52:01 -0700, Don Y >> <blockedofcourse@foo.invalid> wrote: >> >> >Any COMPELLING reason to opt for single multimode fiber, instead? >> >I'm only looking at a few hundred feet run. >> > >> >(the dual fiber solution is "free" for me) >> >> I'm about to get my first articles of a duplex fiber link, ECL in and >> out at maybe 1M to 2 GHz. It's for testing missiles or something. >> >> I'm using a Cisco 10G 850nm multimode SFP module, which is probably >> good for a few hundred meters at my speed. It will run through several >> gymbal joints that have "fiberoptic slip rings" >> >> What's strange is that Amazon wants about $20 for the SFP. Digikey >> wants $94. The list price is $1200. >> >> How fast do you plan to go? Need DC coupling? > >I bought four of those a few years ago on eBay for about $10 in total. >Hardly anyone uses 850nm multi-mode anymore which is why they are so >cheap. >Single mode fibre is now usually cheaper than multimode. > >JohnI think the customer's optical slip ring things only work multimode. It's sort of mind bogling to make a duplex fiberoptic swivel joint, and pipe light through 3 axes of twirling gymbals.
Reply by ●September 22, 20202020-09-22
On 9/22/20 6:47 PM, John Larkin wrote:> I think the customer's optical slip ring things only work multimode. > > It's sort of mind bogling to make a duplex fiberoptic swivel joint, > and pipe light through 3 axes of twirling gymbals.The only slip ring that I've seen was for a single fiber. Hence why we /had/ /to/ use Bi-Di optics over a single fiber. The device we were using was single-mode. But I (naively) assume that there are multi-mode counterparts. -- Grant. . . . unix || die
Reply by ●September 23, 20202020-09-23
On 9/22/2020 5:09 PM, Grant Taylor wrote:> On 9/22/20 5:18 PM, Don Y wrote: >> Good point! I can probably dredge up the necessary SFPs, etc. but I only >> have dual, single-mode fiber available to me, presently, so that's the most >> straight-forward solution... > > If you have dual single mode fiber, you also have two single strand single mode > fiber too. ;-)I don't see what that buys me. IIRC, I can use multimode fiber for single mode operation but not the reverse. So, I'm still stuck with two unidirectional lanes (?)> Use what you have. Worry about changing it later if it ever becomes a problem.It'll never be swapped out. I just need it in place for a demo and then will likely retire the link. (hence my reluctance to *buy* something different unless there was a good reason to do so!) Thanks!