The key performance data targeted by the technology that has been developed at the University of Southampton are impressive: A 5D fused quartz data storage disc suitable for femtosecond laser writing (see info element) is supposed to be able to store up to 500 terabytes of data in a space equal to that of a CD – which would equate to 10,000 times the data density of a Blu-ray disc.

About femtosecond lasers

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Femtosecond lasers are infrared lasers with very weak, short light pulses in the range of femtoseconds. Femto is a unit prefix. One femtosecond (1 fs) equates to 10^–15 seconds. Among other things, these lasers are used in a wide range of medical applications such as dental medicine, ophthalmology (cataract surgery) and cancer therapy.

To illustrate the point: Storing the information contained in all of the 39 million books held by the U.S. Library of Congress in Washington, D.C. on shelves with a length of about 838 miles (1,349 kilometers) would occupy around 20 terabytes. A digital library of the written pages from all the books in the world has a size of some 400 terabytes – and would therefore fit on a single one of these new wonder discs. Or, instead of written documents, 125,000 movies could be stored on such a CD-size 5D storage disc with 500 terabytes. The current record stands at 360 terabytes.

The long life of the data is another advantage of this novel storage device. The scientists estimate that the information stored at room temperature would still be retrievable after 13.8 billion years. By contrast, a Blu-ray disc has a maximum estimated life span of 80 years. The fused quartz storage systems are supposed to be able to withstand short-term exposure even to temperatures of around 1,000 degrees centigrade (1,832 degrees Fahrenheit), which makes them perfectly suited for eternity. “While cloud-based systems are designed more for temporary data, we believe that 5D data storage in glass could be useful for longer-term data storage for national archives, museum, libraries or private organizations,” says Yuhao Lei from the University of Southampton.

Timeline of data storage history

Optimization of existing technology

5D optical data storage in transparent materials per se is not a novelty. In 1996, initial ideas emerged of burning data onto transparent materials using ultrafast lasers. However, it took 17 years to accomplish the leap from theory into practice: in 2013, the scientists in Southampton presented the first prototype of a transparent storage system with data points having been laser-engraved into its structure.

Crystal storage as a Hollywood vision

Don’t be surprised if glass or crystals as data storage devices seem familiar to you – HAL 9000, the computer on board of the Discovery One spaceship featured in the epic Academy Awards winning science fiction movie “2001: A Space Odyssey,” had such a crystal memory, a vision that Stanley Kubrick had as far back as in 1968. And he wasn’t the only one: in the first Superman movie released in 1978, the entire memory of the planet Krypton had been committed to a crystal storage device. So, preserving this classic movie on a crystal disc suggested itself. Microsoft did so in 2019 in its “Silica” project (pictured below).

The advantage of the glass storage discs is remarkable: The engraved data points are tiny nanograting units. These complex structures feature the three commonly known spatial dimensions (length, width, height) and additionally generate two optical dimensions splitting the incident light (double refraction). While the orientation of the light defines the fourth dimension, the retardance caused in the process defines the fifth. That’s why researchers refer to the technology as 5D data storage. Sounds – and is indeed – complicated, but the crucial part is that the interaction of the light enables clearly more information to be stored and read. The data density increases to eight bits per nanograting, not least because the data points with a mere size of 500 by 50 nanometers can be read out from various directions, using a combination of a light microscope and a polarizer, which essentially is nothing but a sunglass lens with a polarizer.

Writing at higher speed

The laser writing technology used in 2013 still had a huge flaw because the data transmission speed was extremely slow. But now the researchers have given the process a boost: by means of an enhanced writing method using laser pulses of varying intensities the nanograting structures are burned into the silica glass disc with both greater energetic efficiency and at much higher speed. “This new approach improves the data writing speed to a practical level, so we can write tens of gigabytes of data in a reasonable time,” says Lei. Furthermore, thermal damage to the grating structure, which kept occurring with the previously used burning method, can be avoided by the ultrashort light pulses.

The UK researchers have managed to write text data onto silica glass discs with nearly 100-percent readout accuracy at a high rate of up to 1,000,000 voxels per second – equating to a data volume of 230 kilobytes or more than 100 pages of text per second.

This new storage technology has been causing a sensation not only on Earth. In 2018, US billionaire and SpaceX owner Elon Musk launched a Tesla Roadster into space aboard a Falcon Heavy rocket for PR purposes. The car had a 5D data storage disc on board with the entire Foundation trilogy – the popular science fiction series by the Russian writer and inventor of the Three Laws of Robotics Isaac Asimov.