In the 90s there was lots of work on storing data in 3d holograms, by using photorefractive materials. That works by interfering a reference wave and an image wave (which contains the information in bit form for example) to create 2d maps and the multiple amps through translation. You can read out the information using a reference wave only. IBM was one of the big research labs in this space.
They achieved some impressive bit densities for the time. There were even some prototypes. However, the rapid increase of drive storage densities and the alignment issues of these systems, (together with the lack of good error correction codes I suspect), meant all this was shelved eventually.
There is now quite a bit of research on using laser writing for storage (Microsoft research is working on this for example). However largely in 2d (3d is difficult because you want 2d read outs for speed and the other layers distort your image), I think they are also thinking about spinning disc type devices, so CD 2.0.
Meh, you only need a little imagination to scan in 3D.
Instead of a disc, use a glass cylinder, mounted excentrically on an axis. (The actual glass cylinder doesn't even have to be excentric for this to work, because the data can be excentrically stored, but it's harder to explain. So assume it's a glass cylinder mounted excentrically on its axis.)
Spin the cylinder on its axis. For each revolution, move the laser one step along the axis. When the laser has reached the end of the cylinder, move the laser one stop closer to the spinning cylinder, then repeat the process in reverse.
The point of the excentricity is to get the "autofocus mechanism for free".
Search speeds could be a dog, but data density and durability could be insane. Plus it would look like something straight out of Star Trek. "Put the data crystal in there."
I think we misunderstand each other (and I've probably caused this confusion because I said CD 2.0). I think they are looking at reading whole 2D images at once, so not a point by point reading process.
