Digital Multilayer Disk (DMD) or Fluorescent Multilayer Storage (FMS) as it used to be called, is now more likely to be an upgrade for DVD technology, if it appears at all. Now that flash storage is mainstream, this seems more and more unlikely.
The technology is owned by D Data Inc and was originally developed by the defunct company Constellation 3D. According to this site, 'the prototype demonstrated (by Constellation 3D) at COMDEX 2000 (was) a hoax — the content was actually playing on a hard drive — the device was faked'.
One of the problems with holographic storage is that the reflected laser light has the same frequency as the read beam, so the two interfere with each
other. FMS works on a different principle. It still uses a laser beam to read multi-layer optical storage, but when it reads the substrate, it emits fluorescent light at a different wavelength. This means there is no interference between the two light beams.
Potentially, this means that FMS can store up to a terabyte in 100 layers on a DVD size disk, and read it back in parallel at 1GB/s. This number has been scaled back since the original announcement to nearer 100GB per disk.
The technology below refers to the 'ClearCard' product as prototyped by Constellation 3D.
The FMS recording media consists of layers of substrate, which contain 'pits' of fluorescent material, each about 0.5um across. These substrate layers are bound together in 10-50 layers, and held on a support platter, which could be like a CD-ROM or like a credit card.
The read heads are very similar to a DVD drive, except they have the ability to read more layers. This means that a FMS drive could read a DVD disk, which could help the product the gain acceptance.
WORM (write once read many) heads use heat to destroy the fluorescent material in selected 'pits', to create a digital pattern. Once the pattern is burnt in, it is permanent.
Constellation 3D planned to roll FMS out in three stages
The technology sounds promising and is still being investigated by other companies, but in 2018 there is no sign of any commercial products.