Fluorescent Multilayer Disc
) was an optical disc
format developed by Constellation 3D
that uses fluorescent
, rather than reflective
materials to store data. Reflective disc formats (such as CD
) have a practical limitation of about two layers, primarily due to interference, scatter, and inter-layer cross talk. However, the use of fluorescence allowed FMDs to operate according to the principles of 3D optical data storage
and have up to 100 data layers. These extra layers potentially allowed FMDs to have capacities of up to a terabyte
, while maintaining the same physical size of traditional optical discs.
The pits in an FMD are filled with fluorescent
material. When coherent light
from the laser
strikes a pit the material glows, giving off incoherent
light of a different wavelength
. Since FMDs are clear, this light is able to travel through many layers unimpeded. The clear discs, combined with the ability to filter out laser light (based on wavelength and coherence), yield a much greater signal-to-noise ratio
than reflective media. This is what allows FMDs to have many layers. The main limitation on the number of layers in an FMD is the overall thickness of the disc.
A 50 GB prototype
disc was demonstrated at the COMDEX
industry show in November 2000. First generation FMDs were to use 650 nm red lasers, yielding roughly 140 GB per disc. Second and third generation FMDs were to use 405 nm blue lasers, giving capacities of up to a terabyte.
After Constellation 3D shut down due to a scandal (the scandal essentially involved the prototype "demonstrated" at COMDEX 2000 being a hoax — the content was actually playing on a hard drive — the device was faked) and the company consequently ran out of money.
A newly formed company called D Data Inc. acquired the patent portfolio of Constellation 3D in 2003, and plans to reintroduce the technology under the new name of Digital Multilayer Disk (DMD).