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Tiny spheres enhance data storage

03 Mar 2005

An optical storage system that uses tiny polystyrene spheres could have a capacity ten times that of a DVD.

An optical storage system with a recording density of up to ten times that of a DVD is under development in Japan. The idea is the brainchild of two researchers from Shizuoka University and uses an array of 500 nm diameter dye-doped spheres placed on a surface-relief grating (Optics Letters 30 299).

“The recording density is double that of a DVD at present,” researcher Naoki Kobayashi told Optics.org. “We think that is possible to increase the density to ten times that of a DVD by reducing the size of the spheres and using three-dimensional stacking and multilevel recording.”

Kobayashi and his colleague Chikara Egami create their storage medium by placing an array of tiny polystyrene spheres onto a grating. Data is recorded by illuminating the array with green light and read out by analysing the reflection of red light. In essence, each sphere acts as a data bit. The recording process changes a sphere’s refractive index so that the sphere is labelled as either a 1-bit (enhanced red reflection) or a 0-bit (weaker red reflection).

The spheres are doped with fluorescent dyes such as rhodamine and a reflection-type confocal system is used to both record and read out the data. The duo uses a frequency-doubled Nd:YVO4 laser emitting at 532 nm to record a bit of data within selected spheres.

The readout process involves firing a 633 nm He-Ne beam through the same confocal system and analyzing the reflection and scatter from the spheres to reconstruct the recorded data bits.

The researchers are now expanding the scheme to make a three-dimensional storage media. “We plan to stack the spheres and are also working on multi-level recording and three-dimensional structuring,” said Kobayashi.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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