[chbot] Fibre optic scraps? / synthetic ulexite?

[Helmut Walle]

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://incomusa.com/faceplate/
https://www.explosionproofvideoscopes.com/fiber-optic-image-bundle/
https://fibertech-optica.com/assemblies/fiber-optic-bundles/
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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