The first CD. This is a standard CD with thermal fax paper laminated on it. It was used for proof of concept. I machined the fixture to hold the CD and the very small diode laser above it. We used an XY stage to move around between 'pixels' that the laser laid down:
One of the first 'special sauce' versions using the same XY fixture:
And another we used for contrast development:
Here'* the lab we did it in (note the white sign above the door):
In the early days, as we were developing the process to work while spinning, it was obvious that we had to know EXACTLY how fast the CD was spinning so as we moved from the inner to the outer diameter, the software could calculate how quickly it had to trigger the laser. Initially, we laser-engraved 'encoder' lines on the hub of the CD drive assembly itself. A small sensor in the drive read the encoder lines in much the same manner as your VSS or WSS on your cars. Now the encoder lines are embedded in the center of the CD itself:
As you can see, it'* not just firmware/software. The drive itself has to be able to read the speed of the disc, and report that back to the software during the entire burn process. It uses the same laser that the data is burned with, but in that mode, it also uses that extra sensor reading the encoder in the disc. As the laser moves from the inner diameter towards the outside edge of the disc, the laser pulses have to be fired more rapidly.
(this information was at one time proprietary, but hp now owns all the patents relating to it, and has licensed the technology to other companies. all this information is displayed at hp now in the aisle just outside my/greyhare'* desks)