Fluorescent Multilayer Disc
Fluorescent Multilayer Disc (FMD) is an optical disc format developed by Constellation 3D that uses fluorescent, rather than reflective materials to store data. Reflective disc formats (such as Compact Disc and DVD) 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.
|Media type||Optical disc|
50 gigabytes (prototype)|
1 terabyte (hypothetical)
|Developed by||Constellation 3D|
|Usage||3D optical data storage|
|Extended to||Digital Multilayer Disk|
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.