# 5D optical data storage

5D optical data storage (also branded as Superman memory crystal, a reference to the Kryptonian memory crystals from the Superman franchise) is an experimental nanostructured glass for permanently recording digital data using a femtosecond laser writing process. Discs using this technology could be capable of storing up to 360 terabytes worth of data (at the largest size, 12 cm discs) for billions of years. The concept was experimentally demonstrated in 2013. Hitachi and Microsoft have researched glass-based optical storage techniques, the latter under the name Project Silica.
The "5-dimensional" descriptor is because, unlike marking only on the surface of a 2D piece of paper or magnetic tape, this method of encoding uses two optical dimensions and three spatial co-ordinates to write throughout the material, which suggested the name '5D data crystal'. No exotic higher dimensional properties are involved. The size, orientation and three-dimensional position of the nanostructures comprise the so-called five dimensions.

## Technical design

The concept is to store data optically in non-photosensitive transparent materials such as fused quartz, which has high chemical stability. Recording data using a femtosecond-laser was first proposed and demonstrated in 1996. The storage medium consists of fused quartz, where the spatial dimensions, intensity, polarization, and wavelength are used to modulate data. By introducing gold or silver nanoparticles embedded in the material, their plasmonic properties can be exploited.
According to the University of Southampton:
   The 5-dimensional discs [have] tiny patterns printed on 3 layers within the discs. Depending on the angle they are viewed from, these patterns can look completely different. This may sound like science fiction, but it's basically a really fancy optical illusion. In this case, the 5 dimensions inside of the discs are the size and orientation in relation to the 3-dimensional position of the nanostructures. The concept of being 5-dimensional means that one disc has several different images depending on the angle that one views it from, and the magnification of the microscope used to view it. Basically, each disc has multiple layers of micro and macro level images.
Recorded data can be read with a combination of an optical microscope and a polarizer.
The technique was first demonstrated in 2009 by researchers at the Swinburne University of Technology and in 2010 by Kazuyuki Hirao's laboratory at the Kyoto University, and developed further by Peter Kazansky's research group at the Optoelectronics Research Centre, University of Southampton. Discs recorded from that time have been tested for 3100 hours at 100°C and shown to still work "perfectly" ten years later.

## Uses

In 2018, Professor Peter Kazansky used the technology to store a copy of Isaac Asimov's Foundation trilogy, which was launched into space aboard Elon Musk's Tesla Roadster in association with the Arch Mission Foundation.
In 2024, Kazansky's group encoded the three billion character human genome and etched it onto a coin-sized 5D disc. It includes a visual key explaining how to use it, in homage to the Pioneer plaques that were placed on board the 1972 Pioneer 10 and 1973 Pioneer 11 spacecrafts. It is stored in the Memory of Mankind archive, located in the world's oldest salt mine in Hallstatt, Austria.