High-speed laser writing could pack 500 terabytes into CD-sized glass disk

Data written in glass

Researchers developed a new fast and energy-efficient laser writing method for producing nanostructures in silica glass. They used the method to record 6 GB of data in a one-inch silica glass sample. The four squares in the picture each measure only 8.8 x 8.8 mm. They also used the laser writing method to write the university logo and mark on the glass. Credit: Yuhao Lei and Peter G. Kazansky, University of Southampton

Advances make 5D high-density optical storage convenient for long-term data archiving.

Researchers have developed a fast and energy-efficient laser writing method for the production of high-density nanostructures in silica glass. These small structures can be used for long-term five-dimensional (5D) optical data storage that is more than 10,000 times closer than Blue-Ray optical disk storage technology.

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

IN OPTICAL, Optica Publishing Group’s journal of high impact research, Lei and colleagues describe their new method of writing data that includes two optical dimensions plus three spatial dimensions. The new approach can write at speeds of 1,000,000 voxels per second, which is equivalent to recording about 230 kilobytes of data (more than 100 pages of text) per second.

“The physical mechanism we use is generic,” Lei said. “Thus, we expect that this energy-efficient writing method can also be used for rapid nanostructuring in transparent materials for applications in 3D integrated optics and microfluidics.”

Faster, better laser writing

Although 5D optical data storage in transparent materials has been demonstrated before, it has proved challenging to write data fast enough and with a high enough density for real world applications. To overcome this obstacle, the researchers used a femtosecond laser with a high repetition rate to create tiny pits that contained a single nanolamel-like structure measuring only 500 times 50 nanometers each.

Instead of using the femtosecond laser to write directly into the glass, the researchers used the light to produce an optical phenomenon known as near-field amplification, where a nanolamella-like structure is created by a pair of faint light pulses from an isotropic nanovoid. generated by a single pulse micro explosion. Using near-field enhancement to make the nanostructures minimized the thermal damage that has been problematic for other approaches using high repetition rate lasers.

Because the nanostructures are anisotropic, they produce birefringence that can be characterized by the slow axis orientation of the light (4th dimension, corresponding to the orientation of the nanolamel-like structure) and retardance strength (5th dimension, defined by the size of the nanostructure). As data is recorded in the glass, the slow axis orientation and retardance strength can be controlled by the polarization and intensity of the light, respectively.

“This new approach improves data writing speed to a practical level so we can write dozens of gigabytes of data in a reasonable amount of time,” Lei said. “The highly localized, precision nanostructures enable higher data capacity because multiple voxels can be written in a unit volume. In addition, the use of pulsed light reduces the energy required to write.”

Writing data on a glass CD

The researchers used their new method to write 5 gigabytes of text data on a silica glass disk the size of a conventional CD with almost 100% readout accuracy. Each voxel contained four bits of information, and each other voxel corresponded to a text character. With the write density available from the method, the disk would be able to hold 500 terabytes of data. With upgrades to the system that allow parallel writing, the researchers say it should be possible to write this amount of data in about 60 days.

“With the current system, we have the ability to preserve terabytes of data that could, for example, be used to preserve information from a person’s DNA, ”Said Peter G. Kazansky, head of the research team.

Researchers are now working to increase the writing speed of their method and to make the technology usable outside the laboratory. Faster methods for reading the data for practical data storage applications must also be developed.

Reference: “High-speed ultra-fast laser anisotropic nanostructuring by near-field enhancement energy deposition control” by Yuhao Lei, Masaaki Sakakura, Lei Wang, Yanhao Yu, Huijun Wang, Gholamreza Shayeganrad, and Peter G. Kazansky, October 28, 2021, OPTICAL.
DOI: 10.1364 / OPTICA.433765

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