As the demand from businesses and consumers for data storage explodes, developers of optical storage technologies are scrambling to condense more and more bytes into a smaller space. Until the promise of holography as a storage medium is realized, fluorescent multilayer discs (FMD) may do quite nicely.

Constellation 3D (C3D) in New York has come up with a method of using red lasers and fluorescent dye to increase to 10 the number of information layers that can be put on each side of a disc, while matching the density and transfer speeds of DVD. In the future, the discs could have as many as 100 layers, according to John Ellis, director of marketing at C3D.

CD-ROMs use one information layer that reflects an infrared laser to supply 650 MB of storage on a one-sided disc. DVDs use a red laser to supply up to 9 GB of storage on a two-sided disc with two layers of storage per side.

In FMD technology, fluorescent dye replaces the reflective and semireflective coating in which information is stored in CD-ROMs and DVDs. This allows for more layers of information, because laser light isn't blocked from traveling deeper into the medium.

There's less noise and interference in the return signal as well, according to Ellis. That's because the fluorescent light that's emitted when a focused laser strikes a pit on one of the information layers has a different wavelength than the laser. The emitted fluorescent light carries the information, and the reflected laser is filtered out in the read device.

Both Philips Electronics NV and IBM have proposed the concept of multilayer reflective optical discs. The reflected coherent light of the probing laser, however, causes interference and cross talk among different information levels that drastically degrade the emitted signal.

The cost of a single FMD may be higher than that of other storage media, but its cost per gigabyte should be considerably lower, according to C3D. FMDs now in development will hold 140 GB of data, as opposed to the 20 GB predicted for next-generation DVDs.

C3D is banking on FMD technology becoming the standard in all kinds of small portable appliances and electronic devices. FMD will allow gigabytes of storage on a disc the size and shape of a credit card. Lev Zaidenberg, C3D's director of business development, says he expects the technology to revolutionize data storage within five years. It will replace CD and DVD technology and will be used in mobile phones, handheld computers, video recorders, PCs, digital cameras and high-definition TVs, he predicts.

Other technologies

Some industry analysts note, however, that users interested in enhanced data storage shouldn't plan on tossing out their CD-ROMs and DVDs soon. Other efforts to accelerate the progress of storage technology have promised much -- some for many years -- but as yet have yielded little.

One of the technologies that hasn't made it out of the laboratory is blue lasers.

With shorter wavelengths and, subsequently, greater storage capabilities than red lasers, blue lasers would burn smaller pits and cram more bits onto removable data. In the mid 1990s, some trade magazines predicted that blue lasers would be in commercial development by 2000. Even with companies like Sony Corp., 3M Co., Philips, and Panasonic Industrial involved in research and development, blue-laser devices remain too unwieldy for commercial applications.

In April 1999, another laser technology, very small aperture lasers (VSAL), was sold by Lucent Technologies to Siros Technologies in San Jose. At the time, the firms touted VSAL as a technique that would "enable significant improvements in data storage density" -- as much as 200 GB to 500 GB per square inch.

Unfortunately, the read-write head in VSAL systems has to be a hard disk drive 25mm from the surface of the disc, requiring assembly in a clean room and making the product appropriate for nonremovable media. This isn't a formula for success in the storage market, where capacity rules and portability is very important.

A similar history can be written of more revolutionary storage ideas such as holography, whose antecedents aren't rotating discs but photography and holography.

The lure of holography is the density of data that can be saved -- about 1 TB in a crystal the size and shape of a sugar cube. The recording material is a photosensitive crystal, which is illuminated by a reference beam and a signal beam. The resulting interference pattern is recorded in the crystal. Shining a reference beam through the interference pattern returns the original signal beam. Entire pages of data can be restored and read simultaneously. The address of the data is the angle and frequency of the reference beam.

The holographic storage "revolution" has been coming since the 1960s and hasn't arrived yet, says Ellis. FMDs provide a large incremental step in optical storage capacity while users wait for the terabyte-holding crystal cube.

» posted by ITworld staff

Computerworld

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