Hi,
my current pet project is a digital optical communications system. For that, I was given a large bunch of old, identical DVD drives (non broken) to salvage parts from. So took the DVD drives' laser diodes, of course with ESD protection.
The first unusual thing I noticed was, that those laser diodes had four, not the usual three connectors. So I spent some time figuring out (or so I think) the pinout:
LD_Cathode LD_Anode PD_Anode PD_Cathode
In the end I had the laser diode shining, regulating up the current and laser operation beginning at around 10mA -- directing it through an etalon I could see the fringes, as soon as coherent radiation was emitted.
Since I have a large number of those diodes I decided to sacrifice one or two to measure their safe operation limits. So I began yanking up the current, expecting COD or some other form of damage at some point. At about 100mA it got dimmer, but to my surprise when I reduced the current back to 10mA it was again emitting bright, coherent radiation (passing through the etalon fringes well visible). So in "vain" I yanked up the current up to 500mA, but still no damage on the laser diode, which isn't what you'd expect.
Any ideas what is going on there?
Wolfgang