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CD-RW Laser diode usage

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uzzors2k

Sat Mar 22 2008, 11:21AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I ripped open a CD burner and scavenged some parts, among them what I'm pretty sure is a laser diode. I tried to determine the pin-out by measuring the voltage across the pins while exposing the diode to light. With a 25W bulb shining directly at the diode, one pin would produce 600mV, while the other did nothing. I've also measured the voltage drop and the pin which produced no voltage had an infinite drop in both directions, while the 600mV pin had a drop of 1.7V.

Is it likely that the working pin is just a photo-diode? I think 0.7V is more common for photo-diodes, and there seemed to be an external photo sensor across from the diode behind a half-mirror. Do CD burner diodes have separate read and burn diodes? Maybe that's why there's three pins, could the open pin have a voltage drop of more than 5V? Also what is a typical current range for CD burner diodes, and how do I know once I've hit the threshold?

lpfthings

Sat Mar 22 2008, 11:39AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

First, i just want to let you know that CD burner diodes are IR, thus they appear only a dim red to the human eye. They are also not very powerful. If you are using it just as an experimental thing, then its fine, but if you want a laser that will do something you will need a DVD burner. Do you have a picture of the pinout? The current ranges vary dramatically from diode to diode, but nothing more than 100ma i would say. You can tell you hit the threshold once it starts producing collimatable light. Below the threshold it may just be like a LED.

Proud Mary

Sat Mar 22 2008, 11:59AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Relative to the Common terminal you should see the following voltages when the device is exposed to strong illumination

~ +500 mV. photodiode anode.
~ -500 mV. photodiode kathode.
~ +5 mV. Laser diode anode.
~ -5 mV. Laser diode kathode.

The voltages will depend on the strength of the illumination, but the photodiode voltage will always be very much higher than the laser diode, because it is more efficient photovoltaic converter.

I'm sure you know already that laser diodes are often extremely vulnerable to ESD, and to even momentary supply line spikes and over voltages.

It is good practice to keep the device terminals shorted with a jumper wire until after the device is soldered into the circuit to reduce the chance of ESD damage.

As a rule, the faster the CD burner, the more powerful the laser diode. 32x burners will have approx 100mW diodes, 48x will have 120mW cw and >200mW pulsed and so on.

CD burners usually work at 780 nm, IR, so you'll need a way of detecting it, and not putting your eye out with the invisible beam.

uzzors2k

Sat Mar 22 2008, 12:32PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

My cell-phone camera can see some infrared, so I can see it real-time without having my eyes anywhere in the beam direction. This is mostly for experimentation, and something to do. It'll also give me some experience if I want to experiment with DVD laser diodes. I saw the voltage measurement trick on Sam's laser faq, which is why I'm a bit concerned about the voltage measurement. Then again I did some googling for datasheets and found that most CD burner diodes have an NC pin and that the case is the cathode. Both of which seem to agree with what I had found.

Mid-post update: I tried it at 20mA and knowing that it will act as a LED I shone it toward the camera, and it works! I'll bring the current up some more and see if it will start lasing.

lpfthings

Sat Mar 22 2008, 11:52PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Well, TBH DVD burner diodes are completely different. They are in a 5.6mm can, and can easily be pushed in to a focusing module. The common one to use are the "Aixiz" modules.

uzzors2k

Sun Mar 23 2008, 12:03PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I took the cheap optics from one of those 2 dollar laser pointers and modified it to fit the diode. The range isn't all that great, but it focuses the beam enough to burn plastic at a few cm distance. I've taken the diode up to 115mA at which point it's voltage drop is 2.5V. I'm not sure how much further is safe to go, so I'll stop there. The power into the diode is 290mW at this point, can I assume 150mW out? What's the typical efficiency of these diodes?

Proud Mary

Sun Mar 23 2008, 01:05PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have a Hitachi HL6504FM laser diode (664nm visible light) module from a DVD burner.

According to the data sheet, it has 50mW Po for Pin ~300mW. (2.6V @ 115mA typical/3.0V @ 135 mA max)

Of course, the technology in your IR unit may be different.

uzzors2k

Sun Mar 23 2008, 06:14PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I went through some datasheets and the efficiency is quite low, but a little more than DVD diodes it seems. Most 100mW units would consume 300-350mW, so I guess mine is closer to 80-90mW.

Conundrum

Mon Mar 24 2008, 03:58PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Anyone have any specs on the diodes used in Liteon DVD burners? I know that the two or so I gutted have virtually identical optics and diodes, however both won't read a DVD.

Apparently this is a common fault with these and many other drives, it looks like the electronics can't handle the normal drop in output power with age properly as the write diode is also used for reading.

Interestingly, I have been told that there is no difference in power between a 4x and a 16x burner, it is the ability to rapidly change power that has been improved (to accurately burn pits and lands). This would be useful to confirm.

I have also discovered that a single CR2032 or CR2025 will run these diodes at around 30% power without cooking them.

Regards, -A

lpfthings

Tue Mar 25 2008, 05:55AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

The liteon drives have open can diodes IIRC. They are much more fragile than a normal closed can, but if you get them heatsinked right, they can be awesome burners at high power. As for the 4-16 thing, i'd have to disagree. Since with the higher X, the disk spins faster, so the laser has less time to etch, thus you need a higher power diode.

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