On Sat, 26 Sep 2020 16:04:13 +0000 (UTC), David Lesher
<wb8foz@panix.com> wrote:
>Grant Taylor <gtaylor@tnetconsulting.net> writes:
>
>
>>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.
>
>My friend does not put connectors on; rather he buys pigtails
>and fusion-splices them onto the run.
>
>He hates to splice multi-mode so badly, we moved to single mode
>just to keep him happy. When you have someone with the right
>tools, just do what he wants.
We order what we need from Fiberopticcableshop.
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by David Lesher●September 26, 20202020-09-26
Grant Taylor <gtaylor@tnetconsulting.net> writes:
>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".
What He Said. The single worst thing about the Valley culture is
the mistaken belief that "New is always better & fixes everything..."
Which leads to everyone abandoning good approaches that need some
refinement, because New is Here!
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply by David Lesher●September 26, 20202020-09-26
Grant Taylor <gtaylor@tnetconsulting.net> writes:
>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.
My friend does not put connectors on; rather he buys pigtails
and fusion-splices them onto the run.
He hates to splice multi-mode so badly, we moved to single mode
just to keep him happy. When you have someone with the right
tools, just do what he wants.
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply by David Lesher●September 26, 20202020-09-26
Don Y <blockedofcourse@foo.invalid> writes:
>That was, essentially, the question: IS there any reason to
>avoid the dual single-mode solution? Yeah, it "looks" a bit
>more dated...
The cost of connectors and terminating doubles. It may be that
is trivial in your case, but if deploying over a large campus,
etc.....
>> Single fiber usually means that you need Bi-Directional
>> optics which are more rare and more expensive.
A friend who deploys systems as I mentioned said sources from
fs.com, amid others & said:
A simplex, dual color (bidi sfp) gigabit SFP module is $12,
a duplex (dual fiber) is $9. So for $6 a link, you can get
by with 1 strand. $6 doesn't even buy the connectors for the
ends of the cable.
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply by Phil Hobbs●September 23, 20202020-09-23
On 2020-09-23 20:18, Chris Jones wrote:
> 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.
BITD expanded-beam connectors were fairly common, but IIRC Amphenol is
the only company making them these days.
> 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.
A Dove prism rotates the image at twice its own speed, interestingly
without doing a great lot to the polarization. (It will go mildly
elliptical, but a single TIR bounce off an air/low index glass causes
way less retardation than a Fresnel rhomb, which is a pretty good
achromatic quarter-wave plate.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Chris Jones●September 23, 20202020-09-23
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.
Reply by Phil Hobbs●September 23, 20202020-09-23
On 2020-09-23 15:50, whit3rd wrote:
> 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).
>
That's not the issue. Fibre modes are orthogonal, and your average
piece of MMF has about 100 of them. Light gets spread out through the
mode volume and loses phase coherence pretty fast, so at the other end
you can couple at most 1% of the light from MMF into SMF, compared with
100% in the other direction.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Phil Hobbs●September 23, 20202020-09-23
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.
Some fibre slip rings intended for solid shafts use one or two MM fibres
on the stationary side, illuminating a split fibre bundle that fans out
into a ring around the outside of the rotating side, so that at least
one Rx fibre is illuminated at all times. That requires a larger
detector, which is slower. Alternatively you can do it the other way
round, which is faster but wastes beaucoup laser power. It's easier at
smaller radii.
One could think of weirder things, e.g. a circular optical waveguide
whose core is exposed on one side, and a sliding tap using some coupling
fluid and frustrated TIR. Dunno if anybody has done that. It would
produce some entertaining data synchronization problems at higher
speeds, but probably not as bad as a sliding metal contact.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Phil Hobbs●September 23, 20202020-09-23
On 2020-09-22 20:47, John Larkin wrote:
> 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.
>
Depending on the application, you can do continuous rotation using the
Indian dancer's trick. Try it with a can of soda: hold it by the
bottom, up near your ear. Rotate it towards you as you pass it under
your armpit and back up next to your ear. Unlimited continuous rotation
without a rotating joint.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Don Y●September 23, 20202020-09-23
On 9/23/2020 12:50 PM, whit3rd wrote:
> 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.
You add a mode conditioning patch cable. You don't magically get all the
benefits of single mode but the cable isn't "wasted" or a multimode converter
needed.
> Two unidirectional lanes isn't 'stuck', it's 'well-equipped' (though having a spare would
> be nice, too).