Saving Data Like Superman

© iStock: Choreograph

Femtosecond lasers are storing data in quartz crystals. Once inside, the information can live on for eternity.

Superman is at a loss. He grabs one of the transparent crystals inside the Fortress of Solitude and thrusts it into the ice. A hologram of his mother, Lara, appears. Superman asks her for advice, and she is able to provide answers to his questions. This is made possible by the fact that the ice crystal is in fact a sort of storage device which contains the entirety of Kryptonian civilization’s knowledge within its structure.

At first glance, the new storage medium developed by scientists at the Optoelectronics Research Centre at the University of Southampton in England, and hailed by the media as the “superman crystal”, appears to have little in common with the device described above: a disk made of nanostructured glass only two-and-a-half centimeters wide.

Heat-Resistance, Durability, Huge Storage Capacity

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The bibel recorded into 5D optical data on the crystal. (Photo: University of Southampton)

And yet the quartz chip is similar to the fictitious crystal in several ways. Among these similarities are its enormous storage capacity. Despite its small size, the disk can store up to 360 terabytes of data (the equivalent of 76,000 DVDs). It can also resist temperatures up to 1,000 degrees Celsius and possesses a virtually unlimited lifetime at room temperature (13.8 billion years at 190 degrees Celsius). What better way to store humankind’s most important documents, such as the Universal Declaration of Human Rights, the Magna Carta or the Bible, in compact digital form for future generations − or beyond?

Three Dimensions: Arrangements in Space

Similar to a standard DVD, data is arranged three-dimensionally. To do this, a femtosecond laser with a wavelength of 1030 nanometers is used to modify tiny zones, or dots, within the crystal. Each of the three dots is assigned a value of 1 or 0, and is thus assigned a bit of information. The minuscule distance between the dots (five micrometers) provides considerable information density and with it a large storage capacity.


Thus the data comes on the disk:


The Fourth Dimension: Structural Orientation via Polarization

Polarization

Light is a propagating electromagnetic field. In natural light, all polarization directions are bundled together. Most laser beams, however, feature a common direction in which they move—the electrical field oscillates in a specific direction. The resulting angle to the direction of propagation is the polarization. So-called wave plates can be used to change the angle of the level of oscillation—that is, the propagation—in a targeted fashion.   

The researchers took things a step further by utilizing an effect caused by high power, ultra-short laser pulses in which specific periodic nanostructures are generated within the quartz crystal’s matrix. The structures are not the result of targeted laser scanning; rather, they form spontaneously as a result of the laser pulse’s high intensity and organize themselves according to variations in the crystal’s optical density. Exactly why and how these structures form is still unknown, but they form all the same.

And they can be used, since their shape is directly related to the intensity and polarization of the laser pulse. By using a wave plate to vary the polarization of the pulse, the researchers were able to change the orientation of the structures inside the dots.

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That is how the structure of the Magna Carta looks like on the quartz crystal. (Photo: University of Southampton)

They selected four angles at which to orient the structures—0, 45, 90 and 135 degrees—, thus assigning each dot four additional states that could be read and two additional bits of information. However, the potential to add even more information exists, since current limits are dictated be the capabilities of the device used to read the angles and not the laser system itself. 

The Fifth Dimension: Size via Pulse Energy

But if that weren’t enough, the researchers were also able to influence the size and density distribution of the matrix structure by using two different levels of pulse energy and, hence, two levels of pulse intensity. This allows each dot to carry an additional bit depending on whether it features a large or small structure. The potential here is also huge, since the size of the matrix structures can naturally be split into more than two gradations of size. The main limiting factor is, once again, the reading device. In total, the crystal can carry four bits of information per dot.

Optical 5D Data Storage Design

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The femtosecond laser uses a repetition rate of 200 kilohertz and a pulse duration of 280 femtoseconds. A spatial light modulator disperses the light intensity on the focal plane and splits the collapsing light into 256 beams. The hologram that appears on the spatial light modulator as a result is then displayed on the back of the objective by an optical 4f system. A wave plate is used to influence the alignment of the electrical field in the laser beam.

The End of Forgetting

The data stored in the crystal is read with the help of a simple optical microscope and a polarization filter. The researchers are currently looking for partners in the industry to help them continue development work on the medium and find a way to commercialize it. High on the list of potential partners are large archives, museums and libraries. Until now, organizations such as these have had to back up their digital archives every ten years. The new superman technology would save them from having to do this in the future. Project head, Professor Peter Kazansky, says: “It is thrilling to think that we have created the technology to preserve documents and information and store it in space for future generations. All we’ve learnt will not be forgotten.”


Superman explains, how his crystal works:


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