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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)
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)
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?
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.
Hardly anyone uses 850nm multi-mode anymore which is why they are
so cheap.
That was, essentially, the question: IS there any reason to avoid
the dual single-mode solution?
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...
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
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.
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. ;-)
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.
John
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.
On 9/22/2020 5:09 PM, Grant Taylor wrote:
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 (?)
I can use multimode fiber for single mode operation but not the
reverse.
On Wednesday, September 23, 2020 at 6:44:11 AM UTC-7, Don Y wrote:
On 9/22/2020 5:09 PM, Grant Taylor wrote:
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 (?)
Oh, no; you cannot use multimode fiber for single-mode operation, because it will
add dispersion and alter polarization... all the benefits of single-mode fiber
are lost. Single-direction operation, yes. Single-mode operation, no.
Two unidirectional lanes isn\'t \'stuck\', it\'s \'well-equipped\' (though having a spare would
be nice, too).
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.
John
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.
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.
That\'s not the issue. Fibre modes are orthogonal, and your averageOn Wednesday, September 23, 2020 at 6:44:11 AM UTC-7, Don Y wrote:
On 9/22/2020 5:09 PM, Grant Taylor wrote:
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 (?)
Oh, no; you cannot use multimode fiber for single-mode operation, because it will
add dispersion and alter polarization... all the benefits of single-mode fiber
are lost. Single-direction operation, yes. Single-mode operation, no.
Two unidirectional lanes isn\'t \'stuck\', it\'s \'well-equipped\' (though having a spare would
be nice, too).
On 2020-09-22 22:46, Grant Taylor wrote:
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.
If you have a hollow shaft and really good bearings, you can do that for
a single channel--it just has to stay within a micron or two of the
rotation axis. MM allows a lot more slop.
On 24/09/2020 07:37, Phil Hobbs wrote:
On 2020-09-22 22:46, Grant Taylor wrote:
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.
If you have a hollow shaft and really good bearings, you can do that
for a single channel--it just has to stay within a micron or two of
the rotation axis. MM allows a lot more slop.
The designs I have seen usually put a collimating lens on the source
fibre and pass an expanded beam across the gap between the rotating
parts, and then focus it onto the receiving fibre with another lens.
That allows a lot more translational slop, though only limited angular
slop (which is probably fine if there is more than one rows of balls /
rollers in the bearing races on the axis).
Some of the multi-channel ones with geared dove prisms look quite
mechanically complicated and expensive, and are probably better avoided
by using some some sort of WDM or digital multiplexing. Still, there
seem to be a lot of fibre optic slip rings available, with up to 16
channels from several suppliers, in a choice of single or multi-mode
versions.
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.