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FrozenGate by Avery

How to collimate a bare diode?

H

Hydrogen

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I have a Pioneer 106D which is a 16x DVDR burner I think, I have the sled ready, I'm going to solder the LM317 later, but is there any way to collimate the bare diode, I have loads of lenses, from old CD/DVD diode sleds, and from a broken camera etc. Will any of them work?
 





Generally you need single convex lens. Plani-convex is better, in which case you put the flat side toward the diode, and curved toward the parallel beam.
You can think of the diode as point light source .. so to get parallel (collimated) beam you have to place the diode in the focal point of the lens.
Also you have to know, that large output aperture will make the beam thicker at the beginning, but it will have lower divergence due to diffraction.
Since most diodes emit at angle about 60 degrees, you need lens which size and focal distance are roughly same .. so if you put diode into the focal point, the beam will cover whole lens. If the beam is wider than the lens, you are not collimating all the energy, if it is smaller, you don't use all lens area and you have smaller effective output aperture.
Common sunglass will work great. Lens in pointers are usually very small, thus very strong (short focal distance).
Some better lens have more elements .. but I'm not quite sure how is that good, probably it should lower the spherical aberration of the lens, but imho the plani-convex should do that pretty well.
Another problem is lens material and coating. You want to minimize the losses. Every air-glass transition will reflect some part of the light .. so better lens use special specific wavelength tuned coating to minimize that. This also usually means that simpler (single element, all mirror setup) is better, as there is fewer air-glass transitions.
Also with non-visible wavelength you might have to use different lens material than glass, as it might not pass that wavelength at all.
 
DrSid said:
Generally you need single convex lens. Plani-convex is better, in which case you put the flat side toward the diode, and curved toward the parallel beam.
You can think of the diode as point light source .. so to get parallel (collimated) beam you have to place the diode in the focal point of the lens.
Also you have to know, that large output aperture will make the beam thicker at the beginning, but it will have lower divergence due to diffraction.
Since most diodes emit at angle about 60 degrees, you need lens which size and focal distance are roughly same .. so if you put diode into the focal point, the beam will cover whole lens. If the beam is wider than the lens, you are not collimating all the energy, if it is smaller, you don't use all lens area and you have smaller effective output aperture.
Common sunglass will work great. Lens in pointers are usually very small, thus very strong (short focal distance).
Some better lens have more elements .. but I'm not quite sure how is that good, probably it should lower the spherical aberration of the lens, but imho the plani-convex should do that pretty well.
Another problem is lens material and coating. You want to minimize the losses. Every air-glass transition will reflect some part of the light .. so better lens use special specific wavelength tuned coating to minimize that. This also usually means that simpler (single element, all mirror setup) is better, as there is fewer air-glass transitions.
Also with non-visible wavelength you might have to use different lens material than glass, as it might not pass that wavelength at all.
Click to expand...


WOW, I cant thank you enough for that post, that is very good.

I have a few convex lenses from CD players/DVD players, they should work.

Can you also suggest me a safe operating current without any heatsink (I can blow a fan on it) for this Pioneer DVR-106D OEM DVD Writer: Amazon.co.uk: Computers & Accessories

Thank you very much.
 
Bad idea. A bare diode will over-heat very quickly. Maybe not at 10mA though.
 
you have to surround the diode with mass and with a press fit. a tec would be useless on a bare diode.

have you extracted the diode from the little heat sink it came in? if not the you could leave it in. if you want more power then possibly use thermal adhesive to mount that on to an alluminum plate. but a tec is over kill.
 
chipdouglas said:
you have to surround the diode with mass and with a press fit. a tec would be useless on a bare diode.

have you extracted the diode from the little heat sink it came in? if not the you could leave it in. if you want more power then possibly use thermal adhesive to mount that on to an alluminum plate. but a tec is over kill.
Click to expand...

I have it in the sled, but I only need to know the current, so I can solder the LM317 driver, then I have to put it all together.
 
Last edited:
if you have the time and an accurate multi meter, i would do time/heat tests at 10ma intervals. i would start at 10ma and go up. the tricky part with you is that we don't know what you are trying to do. and you are using a tiny heat sink. LD's can generate a lot of heat quickly. so i would say burning matches while mounted in the sled is highly un likely.
 
chipdouglas said:
if you have the time and an accurate multi meter, i would do time/heat tests at 10ma intervals. i would start at 10ma and go up. the tricky part with you is that we don't know what you are trying to do. and you are using a tiny heat sink. LD's can generate a lot of heat quickly. so i would say burning matches while mounted in the sled is highly un likely.
Click to expand...

I dont have multimeter (I broke it when it accidentally struck my Tesla coil)

I will buy one if needed, soon.
 
oh the old "it accidentally struck my tesla coil" excuse.... Well an aixiz module to mount your diode in comes with a lens and is a pretty good heatsink. you can easily find them for about 4bucks usd. and you can mount that and an lm317 and batteries into almost anything.

michael.
 
chipdouglas said:
oh the old "it accidentally struck my tesla coil" excuse.... Well an aixiz module to mount your diode in comes with a lens and is a pretty good heatsink. you can easily find them for about 4bucks usd. and you can mount that and an lm317 and batteries into almost anything.

michael.
Click to expand...

Awesome thanks for all your help :bowdown:
 
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