# Lasers harvested from scrap CD/dvd drives.



## ianfield (Mar 31, 2013)

Whenever I scrap an old CD/DVD drive, I usually harvest the laser - someday I might get around to experimenting with them. As the vast majority do not have type numbers, telling the difference between the laser junction and the detector diode is just one of the hurdles to firing it up - DVD lasers generally have 2 laser junctions (one of which is non-visible IR) which serves only to add to the confusion. Is there any way to sort the emitters from the detectors in the absence of any data sheets?Thanks for any help.


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## AnAppleSnail (Mar 31, 2013)

Thermocouple to aid testing?


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## bshanahan14rulz (Apr 1, 2013)

The emitters are the ones with the laser diode chip in it 

All smart-assery aside, detectors generally look a lot 'cheaper,' i.e. plastic backing, encapsulated in clear resin, while the diodes will generally be in a metal can, like this image: http://4.bp.blogspot.com/-B1iPej24xCQ/TZJtVzC9PsI/AAAAAAAABl0/EDAcGf6Knjc/s1600/Laser_diode-26.jpg < not my image, just googled to find it.

To add to the confusion, you're lucky if your diodes have any markings, much less markings that can be decoded with publicly available info.

Some odd diodes will actually be in one of those plastic, encapsulated packages, mounted onto the detector chip, so if you have a detector but can't find it's emitter, look closely at the detector and you may see an extra chunk of semiconductor sticking out from the surface of the detector chip.


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## ianfield (Apr 1, 2013)

bshanahan14rulz said:


> The emitters are the ones with the laser diode chip in it
> 
> All smart-assery aside, detectors generally look a lot 'cheaper,' i.e. plastic backing, encapsulated in clear resin, while the diodes will generally be in a metal can, like this image: http://4.bp.blogspot.com/-B1iPej24xCQ/TZJtVzC9PsI/AAAAAAAABl0/EDAcGf6Knjc/s1600/Laser_diode-26.jpg < not my image, just googled to find it.
> 
> ...



I thought you were going to put "All smart-assery aside"! I was referring to the emitters & detectors that share the same encapsulation in a typical CD and/or DVD laser device - and for your information, the devices range from professional looking similar to TO18 encapsulation to real cheap & nasty block of plastic with wires from one end.


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## bshanahan14rulz (Apr 1, 2013)

Ah, gotcha. You are trying to find out, of the three pins, what the pinout of the diode is, assuming there is an internal photodetector inside the "TO-56" package? I would be willing to bet that your diodes will most likely not have an integrated photodetector if they were pulled from consumer grade optical drives. I haven't harvested many, only about 15 drives total, and only one of them had the laser diode and photodetector all in one package. It was a clear, cube-shaped package with a diffraction based optic, and you could see a tiny laser resonator mounted on a pedestal off to the side of the photodetector.

I think, mainly the photodetector is used for laser output stabilizing, less for signal detection on the return trip.

The cheap and nasty block of plastic with wires from one end, sounds like one of the open-air plastic diodes, decent performance, but once you take them out of teh drive, they are hard to keep clean and mount in standard hobbyist mounts (aixiz style)
(found this image of the two common harvested diode packages while looking for a different post: http://www.emred.fi/images/laser_diode_structure.gif)
http://laserpointerforums.com/f50/flat-red-laser-diode-testing-2nd-phase-47044.html < this has a bit of info on one type of flat plastic diode that people have found.

http://laserpointerforums.com/f51/diodes-compilation-all-diodes-data-one-thread-45042.html < I was gonna try to find an image of the pinout, most reds have the same pin-out as IRs, but this thread is much more useful.


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## ianfield (Apr 2, 2013)

bshanahan14rulz said:


> Ah, gotcha. You are trying to find out, of the three pins, what the pinout of the diode is, assuming there is an internal photodetector inside the "TO-56" package? I would be willing to bet that your diodes will most likely not have an integrated photodetector if they were pulled from consumer grade optical drives. I haven't harvested many, only about 15 drives total, and only one of them had the laser diode and photodetector all in one package. It was a clear, cube-shaped package with a diffraction based optic, and you could see a tiny laser resonator mounted on a pedestal off to the side of the photodetector.
> 
> I think, mainly the photodetector is used for laser output stabilizing, less for signal detection on the return trip.
> 
> ...



The most recent acquisition was from what appeared to be a cheap & nasty DVD player, the laser device was in a top grade looking TO 18 style case with 4 pins - presumably red laser, IR laser PD & GND. I could try powering up with; say 70 - 80mA, but the invisible IR is potentially dangerous and that much current probably won't do the PD much good - the red laser pins should be easy to find, but how do I tell the difference between the invisible IR & the PD which doesn't emit anything - is there a discernible difference between the various junctions Vf that I can see with the diode check on my DMM?


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## bshanahan14rulz (Apr 2, 2013)

The Vf of the IR diode will be a smidge lower than the red.

Also, you could power it with a low current, and use a cheap digital camera to detect infrared. The camera's sensor can pick up the IR, and will display it as a pinkish white hue. Try it with a TV remote and whatever digital cameras you have available.


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## ianfield (Apr 2, 2013)

bshanahan14rulz said:


> The Vf of the IR diode will be a smidge lower than the red.
> 
> Also, you could power it with a low current, and use a cheap digital camera to detect infrared. The camera's sensor can pick up the IR, and will display it as a pinkish white hue.



I've used a digital camera before - but it isn't easy without 2 pairs of hands. There is always some risk with an invisible IR beam.


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## bshanahan14rulz (Apr 2, 2013)

Yeah, I would suggest powering the bare diode (no optics) with low current when testing. The raw output should diverge fairly quickly (i.e. a foot away, the spot would be like, 5 inches "diameter"). If you do a search in google, there are a few Power vs Current plots for various common laser diodes, and most of these diodes are harvested from DVD burners, just like what you are doing.

a few generic datasheets for you:
http://www.me-sh.cn/products/pdf/ml1xx27.pdf
The Infamous "Long, Open Can" diode: http://redlum.xohp.pagesperso-orange.fr/electronics/data/ML101U29.pdf

At Ith, the resonator will start lasing. Under Ith, you still might get some incoherent radiation. I'd say that's a good value to start testing with.

I hear some PSUs can have nasty spikes when you first start cranking up current or voltage from 0, so you might consider trying on what you think may be a crappier diode, like one of those plastic ones.

Have fun, but be safe! I don't think you will get hurt if you keep your current limited relatively low and don't use any additional optics, but still, make it a point to have these devices pointing away from you when testing. You can have a piece of paper or something as a target, and have your digital camera set down and pointing at the target too while you test, so that both you and the camera are only viewing radiation indirectly.


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## ianfield (Apr 3, 2013)

bshanahan14rulz said:


> Yeah, I would suggest powering the bare diode (no optics) with low current when testing. The raw output should diverge fairly quickly (i.e. a foot away, the spot would be like, 5 inches "diameter"). If you do a search in google, there are a few Power vs Current plots for various common laser diodes, and most of these diodes are harvested from DVD burners, just like what you are doing.
> 
> a few generic datasheets for you:
> http://www.me-sh.cn/products/pdf/ml1xx27.pdf
> ...



Thanks.


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