China Breakthrough Promises Optical Discs That Store Hundreds Of Terabytes

Optical discs that can store up to 200 TB of data could be possible with a new technology developed in China. If commercialized, it could revive optical media as an alternative to hard disk or tape for cost-effective long-term storage.

Researchers at the University of Shanghai for Science and Technology (USST) and Shanghai Institute of Optics and Fine Mechanics (SIOM) say they have demonstrated that optical storage is possible up to the petabit level by using hundreds of layers, while also claiming to have broken the optical diffraction barrier limiting how close together recorded features can be.

In an article published in Nature titled "A 3D nanoscale optical disk memory with petabit capacity," the researchers detail how they developed a novel optical storage medium they call dye-doped photoresist (DDPR) with aggregation-induced emission luminogens (AIE-DDPR).

When applied as a recording layer, this is claimed to outperform other optical systems and hard drives in terms of areal density – the amount of storage per unit of area. To be specific, the researchers claim it to be 125 times that of a multi-layer optical disk based on gold nanorods, and 24 times that of the most advanced hard drives (based on data from 2022).

The proposed recording and retrieval processes for this medium calls for two laser beams each. For optical writing, a 515 nm femtosecond Gaussian laser beam and a doughnut-shaped 639 nm continuous wave laser beam are focused on the recording area.

Here, the first beam initiates the polymerization, which is deactivated by the second beam, resulting in a recording spot with what the researchers call a "sub-diffractive volume size," meaning smaller than would otherwise be possible. For reading, a 480 nm pulsed laser and a 592 nm continuous wave laser are used.

According to the researchers, blank disks with the AIE-DDPR film can be manufactured using a process compatible with the standard workflow for conventional DVDs involving spin-coating and a process for blank disk molding.

In tests, the researchers claim the AIE-DDPR film is so transparent that they were able to write and read up to 100 layers on such disks, with a distance between neighboring layers of just 1 micrometer (1 μm).

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The data used for this was actually the USST and SIOM logos written into alternating layers, and the team states that when read, the even and odd layers had clear alternating patterns with no cross-talk, and the resolution of the pattern in the deeper layers was found to be comparable to that in the upper layers.

With 100 layers to a disc plus a minimum spot size of 54 nm and a lateral track pitch of 70 nm, the researchers estimate this should make possible a capacity of 1.6 petabits (200 TB) within the area of a DVD-sized disc.

However, they caution that although this increases the areal density of storage substantially, improvements in writing speed and energy efficiency are needed for commercial viability. This could be accomplished by using a femtosecond laser beam with a higher repetition rate and a more sensitive photoresist than those used in the current system.

This means the nanoscale optical storage system is some way off from any commercial availability of drives and media, but the researchers assert that such products should prove less costly than current state-of-the-art optical disc libraries and hard drive arrays for meeting the vast data storage requirements of the AI era.

Flash storage and disk drives also have high energy burdens, they claim, leading to high operation costs and short lifespans, while optical media can store data safely for decades.

However, for archive purposes, the tech may not have much of a lead over plain old tape technology. Last year, IBM announced the TS1170 tape drive with 50 TB cartridges, which are capable of storing up to 150 TB through 3:1 compression. ®