Researchers have presented a method of recording up to 1TB of data in three-dimensions throughout the volume of a standard-size (120mm x 1.2mm) optical disc, which has hundreds of layers.
The research paper was published in this week's edition of Applied Optics
and describes the latest experiments of the California-based Call/Recall, a company that provides advanced research into optical storage technologies and ultra-high storage solutions.
Call/Recall supports a patented 2-photon recorded 3D optical storage technology that can provide 40 times the capacity of Blu-ray.
2-Photon-3D uses a special "near-field" lens and fluorescent media technology to record hundreds of layers three-dimensionally. 2-Photon-3D offers more than DVD recording because the near-field lens can dynamically focus into the depth of the fluorescent media, taking advantage of the full depth of standard 120mm, DVD-size media to achieve recording densities as good as holographic technologies.
The company has developed a series of stable two-photon 3D recording materials using photochromic fluorescence compounds that are well suited as media for 3D optical storage memory devices.
The disc is composed of two components: a photoacid generator (PAG) and a dye precursor (DP). Both were uniformly dispersed in a polymer host such as polymethyl methacrylate (PMMA). The PAGs used are light sensitive compounds that are thermally stable, however when excited with light of the appropriate wavelength, two 532 nm photons in this case (disc recorded using a 532nm laser) undergoes photochemical reaction that results in the generation of acid.
The dye precursor molecules are thermally stable, colorless non-fluorescing molecules, that react with the produced photo-induced acid and are transformed to strongly fluorescent dye molecules with absorption maximum at 650 nm. After recording, a compact 650 nm CW diode laser was used to excite the dye and induce the dye to fluoresce. The readout fluorescence is detected by a photodiode and used as the 1 in the computer code, while the non-fluorescing bits are used as zero.
The researchers managed to record 1 Tbyte of data in 200 layers inside the volume of one of our two-photon 3D disks. Each layer contains 5 Gb of data similar to the capacity of a single layer DVD.
The researchers also experiment on materials sensitive at 405 nm by recording with a 405 nm Nichia laser diode. Using very high sensitivity materials, they claim that they will be possibly be able to record data with bit energies as low as 250 pJ/bit ?a 24th of the power used in their current test device.
The results showed that bit dimensions are further reduced, which enables future recordings of 5 Tbyte disk capacities by recording 25 Gb/layer, the equivalent of a Blu-ray disk capacity per layer.
Although the paper provides a proof of concept of the new technology, there is no indication that such a system will be released on the market anytime soon.