Researchers develop 5D optical data storage method that can preserve up to 5TB per disc

Optica has announced that researchers at the University of Southampton in the UK have developed a fast, efficient laser-writing method for producing high-density nanostructures in silica glass. Per Optica, the high-density nanostructures can be used for long-term five-dimensional (5D) optical data storage that is more than 10,000 times denser than Blu-Ray optical discs.

'Individuals and organizations are generating ever-larger datasets, creating the desperate need for more efficient forms of data storage with a high capacity, low energy consumption and long lifetime,' said doctoral researcher Yuhao Lei from the University of Southampton. 'While cloud-based systems are designed more for temporary data, we believe that 5D storage in glass could be useful for longer-term data storage for national archives, museums, libraries or private organizations.'

'Laser writing of birefringence structures inside silica glass. (a) Schematic of laser writing setup. EOM is an electro-optic modulator and QWP is a quarter-wave plate. (b) Images of the slow axis azimuth of voxels written by 100 laser pulses with the energy of 30 nJ at different repetition rates from 1 to 10 MHz; the pulse duration and wavelength in (b) are 250 fs and 515 nm, respectively. Pseudo-colors (inset) indicate the local orientation of the slow axis.' Caption and image credit: University of Southampton; Lei, Sakakura, Wang, Yu, Wang, Shayeganrad, and Kazansky

In Optica's journal, Lei and colleagues describe their new method. The method utilizes two optical dimensions and three spatial dimensions. The novel approach can write at speeds of 1,000,000 voxels per second, which is equivalent to 230 kilobytes of data per second. This isn't spectacularly fast speed, but the draw of the new technology isn't its speed, it's the immense storage capacity in a relatively small physical space. However, the new approach is relatively fast.

This isn't the first time that 5D optical data storage has been demonstrated. However, previous approaches have had limited application due to slow data writing and insufficient density. To overcome these challenges, the researchers in Southampton 'used a femtosecond laser with a high repetition rate to create tiny pits containing a single nanolamella-like structure measuring just 500 by 50 nanometers each.'

Image credit: Optica

'The physical mechanism we use is generic,' said Lei. 'Thus, we anticipate that this energy-efficient writing method could also be used for fast nanostructuring in transparent materials for applications in 3D integrated optics and microfluidics.'

Optica writes, 'Because the nanostructures are anisotropic, they produce birefringence that can be characterized by the light's slow axis orientation (4th dimension, corresponding to the orientation of the nanolamella-like structure) and strength of retardance (5th dimension, defined by the size of nanostructure). As data is recorded into the glass, the slow axis orientation and strength of retardance can be controlled by the polarization and intensity of light, respectively.' With precise localization of nanostructures, capacity is increased. Further, by using pulsed light, the energy demand for writing is reduced.

'Imaging of anisotropic nanostructures. (a) Image of the slow axis azimuth of voxels induced by two seeding pulses (E𝑠=36nJ) and eight writing pulses (E𝑤=16.8nJ) with a repetition rate of 500 kHz and the pulse duration of 190 fs at 515 nm wavelength. The pseudo-color represents the slow axis azimuth. (b) SEM image of the nanolamella-like structure after polishing and KOH etching; (c) enlarged area in the dashed square in (b); (d) SEM image of isotropic nanovoids created by two seeding pulses; (e) simulation of the evolution from a nanovoid to a nanolamella produced by two (eight) writing pulses for top (bottom) image. The nanovoid diameter is 160 nm, estimated from the SEM image. The polarization direction (E) is indicated in the figure, and the laser beam propagation direction is perpendicular to the screen.' Caption and image credit: University of Southampton; Lei, Sakakura, Wang, Yu, Wang, Shayeganrad, and Kazansky.

In testing, the team has used their new method to write 5GB of data to a silica glass disc about the size of a traditional CD. However, the method's writing density means you could put 500 terabytes of data on the same disc. It would take about 60 days to write this amount of data with an upgraded system that can perform parallel writing.

'With the current system, we have the ability to preserve terabytes of data, which could be used, for example, to preserve information from a person's DNA,' said Peter G. Kazansky, leader of the researcher team.

'Optical data storage of 5 GB data. (a) Schematic diagram of raster scanning by stage translation and (b) combination of raster and AOD scanning. Each green circle indicates one data voxel, and the numbers show the temporal sequence of data recording. (c) Birefringent voxels written by the combination of the PEM and AOD with 10 channels. The pulse trains include one seeding pulse and seven (or four) writing pulses (515 nm, 250 fs, 10 MHz, 96 mm/s, 9.6×105voxels/s). Pseudo-colors (inset) indicate the local orientation of the slow axis. (d) Distribution of the readout data points from (c) with eight azimuths of slow axis orientation and two levels of retardance. (e) Illustration of data encoding and decoding.' Caption and image credit: University of Southampton; Lei, Sakakura, Wang, Yu, Wang, Shayeganrad, and Kazansky.

The researchers are now working to increase the writing speed of their method and make the technology usable outside of a laboratory setting. For the method to make practical sense, faster reading methods will also need to be developed. However, for archival data storage, the new technology is fascinating.

If you'd like to read the paper, High speed ultrafast laser anisotropic nanostructuring by energy deposition control via near field-enhancement, visit Optica Publishing Group. The paper's authors are Yuhao Lei, Masaaki Sakakura, Lei Wang, Yanhao Yu, Huijun Wang, Gholamreza Shayeganrad and Peter G. Kazansky.

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