[chbot] molten media / fibre optics

Sun Dec 4 09:10:58 GMT 2022

Good question. But it may help not to think of the Ulexite "doing" something. Ulexite is just a 
natural mineral that happens to have certain interesting optical properties, completely free of 
objectives. This makes it different from human-made technology that we have developed with 
certain objectives in mind.

For optical fibres we are usually interested in conducting light efficiently over some distance, 
and in many cases with minimal dispersion. These objectives lead to products that require 
bundling the optical energy onto a small spot at the end of the fibre, and often within quite a 
limited angle (numerical aperture). At the same time we do not want ambient light to couple into 
the fibre, because that could interfere with the signal that we want to transmit.

Ulexite, on the other hand, is not fraught with any such constraints, and it just is what it 
is... which is essentially a block of crystals formed by the mineral interleaved with water 
molecules, resulting in a crystal structure that guides light through reflection on internal 
boundaries, while at the same time being open to light coming in from the sides, allowing for 
good illumination of the object below. That object will usually reflect diffusely or scatter the 
incident light, that will then by and large travel to the top via the paths allowed by internal 
reflection.

Sooo... to replicate that effect I would suggest to disregard high-performance long-distance 
telecommunications fibres and instead go for something that is essentially just a "wire" made 
from transparent material, which could be either glass or plastic, because signal attenuation is 
not goint to matter much for a device that is only a few centimeters thick. I believe there are 
cheap lamps that may use that kind of plastic "wire". Something like this maybe 
https://www.aliexpress.com/item/32979843341.html (Or are they using glass fibres? Even so, they 
might still work, as they are probably "core-only" fibres in that case.)

The simplest arrangement would be a bundle held together by a cylindrical ring of some sort, 
maybe even a hose clamp, at both ends. As mentioned before filling the gaps with resin may be 
counterproductive, unless the resin is known to be of lower refractive index than the wire material.

Then, from seeing the word "fused" in the description of the fibre optic faceplate referenced 
below, it may be worthwhile experimenting with that idea to get the fibres closer together, and 
to reduce the volume of air between them, possibly also to secure them to each other. So if the 
material is plastic, gently heating the whole arrangement to a temperature somewhat below 
melting point may allo the fibres to change from a usually circular cross-section to something 
more hexagonal and lightly bonded... But I would expect this procedure to require some 
experimentation, and that one manufacturer of these faceplates is using glass and my well have a 
patent or two on the production method. If that is the case the patents might be informative too.

All the best for your experiments, and let us know how it's going.

Kind regards,

Helmut.

On 04/12/2022 02:31, andrew dean wrote:
[...]

> As to the fibre optic not having enough light to xmit or a surface to project on... How does 
> ulexite do that?
> 
> -a
> 
[...]

> 
>     Message: 5
>     Date: Sat, 3 Dec 2022 22:13:10 +1300
>     From: Helmut Walle <helmut.walle at gmail.com <mailto:helmut.walle at gmail.com>>
>     To: chchrobotics at lists.ourshack.com <mailto:chchrobotics at lists.ourshack.com>
>     Subject: Re: [chbot] Fibre optic scraps? / synthetic ulexite?
>     Message-ID: <d13ef30f-2f40-6c3a-a19c-7cda2f850f41 at gmail.com
>     <mailto:d13ef30f-2f40-6c3a-a19c-7cda2f850f41 at gmail.com>>
>     Content-Type: text/plain; charset=UTF-8; format=flowed
> 
>     Sounds a bit like a fibre optic faceplate, which exists as a commercial product. But while
>     possible in principle, this idea of embedding fibres in resin is unlikely to work well in
>     practice, because:
> 
>     a) a visible image relies on the presence of light that the eye can see; but how will you
>     illuminate the original image if you put the flat image-sized fibre bundle on the original?
>     (Sure, if the original is translucent you can illuminate from the back... In theory you could
>     also illuminate from the viewing side of the fibre bundle through the same, however in order to
>     make that work you would need a polished transparent surface there, and that would then mean
>     that the transferred image simply exits the same polished surface without becoming visible...)
> 
>     b) if you are thinking of using telecommunications optical fibre it won't work well if at all,
>     because that kind of fibre consists of a core and cladding, where only the core transfers
>     light,
>     however the cladding takes up the larger part of the cross-section - so you won't be able to
>     couple much light into the fibres. So you are probably looking at using something like these
>     transparent plastic wires used in fibre optic decorative lamps. However, these are very
>     probably
>     made from just one plastic material, thus relying on the refractive index step from the plastic
>     to the surrounding air. If you are embedding them in a resin then that resin needs to have a
>     lower refractive index than the wire to make it work. Even so, it probably won't work well -
>     see
>     point a) above.
> 
>     c) even if you can couple a sufficient amount of light into the end of the fibre bundle sitting
>     on the original, how are you going to make the image visible on the open end? The simplest
>     approach might be to frost that end by sanding it finely. But that will be very inefficient as
>     it will lead to a further loss of light, because much light will simply pass through into the
>     open air and will thus be lost for imaging.
> 
>     I would think it may work somewhat, maybe to a degree where you can see something in a dark
>     room, but it is highly unlikely that this will be useful as a daylight application with
>     reasonable effort.
> 
>     All of that being said, fibre optic imaging bundles are commercially available, but they are
>     generally being used together with optics that couple the original image into the fibre bundle
>     efficiently at the object end, and further optics that efficiently couple the image out of the
>     fibre bundle at the viewing end. These bundles are used for applications like endoscopes. And
>     then there are the aforementioned fibre optic faceplates. More info on them here
> 
>     https://www.photonics.com/Category.aspx?CatID=24500
>     <https://www.photonics.com/Category.aspx?CatID=24500>
>     https://incomusa.com/faceplate/ <https://incomusa.com/faceplate/>
>     https://www.explosionproofvideoscopes.com/fiber-optic-image-bundle/
>     <https://www.explosionproofvideoscopes.com/fiber-optic-image-bundle/>
>     https://fibertech-optica.com/assemblies/fiber-optic-bundles/
>     <https://fibertech-optica.com/assemblies/fiber-optic-bundles/>
>     https://www.edmundoptics.com/f/fiber-optic-image-conduits/11464
>     <https://www.edmundoptics.com/f/fiber-optic-image-conduits/11464>
> 
>     All of this stuff is pretty hard to make on your kitchen bench.
> 
>     And regarding question "2. Would gluing fibre optic strands together ruin their optical
>     isolation?" - it depends... If you are doing this with telecommunications fibre (either
>     monomode
>     or multimode) it won't affect their performance, because they have a well-defined optical
>     cladding layer around the light-conducting core. But if you are using a plastic "wire" made
>     from
>     one homogenous material then embedding in a resin may well destroy its light-conducting
>     properties, particularly if the refractive index of the resin is the same or greater than that
>     of the "wire".
> 
>     I would recommend getting the physics of the whole system sorted first before starting to
>     experiment.
> 
>     Kind regards,
> 
>     Helmut.
> 
> 
>     On 03/12/2022 19:20, Mark Atherton wrote:
>      > Sounds possible to me. The trick may be to keep the bundle coherent during gluing.
>      >
>      >
>      >
>      > On 12/3/2022 6:29 PM, andrew dean wrote:
>      >> I’ve been obsessed with ulexite for years and was curious if I could make a high quality
>      >> synthetic by using epoxy resin to glue a bunch of fibre optic pieces together that I could
>      >> cut/turn/mill into a solid that would (ideally) have the weird quality of making an image
>      >> appear on the top of it.
>      >>
>      >> 1. You reckon it would work?
>      >> 2. Would gluing fibre optic strands together ruin their optical isolation?
>      >> 3. Know anybody with some scrap optical wire or a super cheap source for fibre optic
>      >> scraps/b-grade stuff I could play with?
>      >>
>      >>
>      >> Cheers!
>      >> -Andrew
>      >> (No, the other one)
>      >> ...
>      >> (Not that one either)
>      >> ...
>      >> (Ok, fine... <sigh> the fat American one… yeah, that one.)
>      >> _______________________________________________
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