How to make your own fat optical fiber for solar device?

I'm prototyping a solar energy device, and need to transport a concentrated light beam a couple of meters without loss or, ideally, burning anyone's hand off. I was thinking of some kind of 'total internal reflection' medium, such as glass, but it needs to be cheap and easy to make/find, and it would be great if it had at least a little flexibility. Is there any way to make your own? Some kind of gel, or crystal, or maybe water if it wouldn't attenuate or absorb too much of the energy? Failing that, is there some existing material I could wrench out the back of something? Cheers, Daniel.

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SolarFlower_org (author) 9 years ago
A guy over at Makezine is recommending mineral oil (aka liquid paraffin) as a liquid medium for a light pipe. It has an refractive index of 1.46 and boils at about 300 C. And is cheap as chips. What do you guys reckon? Lenses are a good idea, but I'm not sure how easily sourceable they'd be in some parts of the world. And how would they hold up to high temperatures, and how much energy is lost going through them? But I will have to use them if I can't get the mirrored surfaces exact enough. This is all really helpful, thanks heaps guys.
NachoMahma9 years ago
. For what you're doing, mirrors and air will probably work best. If you have to have a cable of some sort, look into the light pipes used for lasers.
SolarFlower_org (author)  NachoMahma9 years ago
A beam through air is an option, and if the whole pipe thing doesn't work out (which I was kind of suspecting it wouldn't) then that's the way I'll probably have to go. The only problem with that (other than having to make a protective housing so no one walks through it) is if I'm firing this thing a couple of meters the beam will probably lose focus by a fair amount. But I guess that comes down to how well I make the reflective surfaces. Also, there's the question of what to use for mirrors. Standard glass mirrors aren't actually as reflective as you might think, and something like Mylar might not handle the heat. Thanks for the input guys. I've been looking into light pipes, they would be perfect, if I could get just about anywhere...
You need to look for "first surface" mirrors - most mirrors are silvered on the back, and the light has to ravel through the glass twice, refracting at the air/glass boundary each time. "First surface" mirrors, as the name implies, are coated on the front, reflecting much more light.

To prevent it losing focus, you need a lens to collimate the beam, that is, turn the beam of light from a spreading cone to a parallel-sided cylinder. If I've not made that clear, look at this sketch - imagine the your focussed sunlight in place of the bulb.
  • Standard glass mirrors aren't actually as reflective as you might think
I don't think that most optical fiber is as transmissive as you think, either, except perhaps over a small frequency range.

I found an An interesting link that implies that a heat-pipe is more efficient than an optical waveguide.
SolarFlower_org (author) 9 years ago
Ok, so. Thanks for the heat pipe mention, I've been doing some research. They do seem to be very efficient, but there would be several problems using them here: They work partly on capillary force, using a metal or ceramic wick, which makes them a little tricky to construct, and kind of limited in length and vertical orientation. ie, the shorter and flatter, the better. At these temperatures you'd have to use a fluid medium like sodium, or something else with a very high boiling point. They'd need to be solidly constructed and very well insulated. So I don't think I could use that here, which is a shame because they're pretty cool. Getting back to light pipes: A good silica or acrylic pipe will give transmittance of about 95-98% per meter, which isn't too bad. If you can get good silica or acrylic. I've been looking up optical gels and supersaturated solutions as possible mediums but haven't found anything yet that could be easily produced. Hmm.
kelseymh9 years ago
As killerjackalope wrote below, what you want is a light pipe. Go to a local plastics supplier (we have a company called "TAP Plastics" in California) and get a couple of meters of 3-5 cm acrylic cylinder. That should be flexible enough for your needs. You will need to polish the ends, and if you want to attach the pipe directly to your light source, then you should get some optical grease. Otherwise there will be a mismatch in indices of refraction and you'll get reflective losses.
If the beam's already been made straight then it could work with alot of things, like those prism bars, old science depts. throw a lot out in favour of acrylic ones, however both could be got on Ebay. I don't know if plastic would hold up to that punishment, Also, test all incidence angles before starting the mirrors on it, you might break reflection and start a fire...
The beam entering will be pretty much unidirectional and perpendicular. The thing taking the light will need to be kind of hose-like. ie long, skinny, and somewhat flexible. It'll also have to have no breaks or internal surfaces, etc. Water will do it, but I can't see as even with really clear water it won't just start boiling...
Hmm light pipes and fibre optics use their surfaces, it bounces off the edge of it, though the angles are critical to it functioning... Mirrors would probably be an easier solution, if you're trying to move the light beam around afterwards then a mirror at the end that's very finely controlled by a couple of motors so it can pan and tilt would do nicely... Not trying to put you off the idea it's just likely to be incredibly expensive to use fibre optics. You could use prisms instead of mirrors aswell... Maybe an old periscope or even making one could be a good arrangement, then you'd have freedom of movement and a fairly simple setup.