Sub-diffraction Optical Writing Information Bits: towards A High-Capacity Optical Disk for Big Data

The total amount of data generated worldwide is expected to reach 175 ZB (Zettabytes; 1 ZB equals 1 billion Terabytes) by 2025. If 175 ZB were stored on Blu-ray disks, the disk stack would be 23 times the distance to the Moon. They face the urgent need to develop storage technologies that can accommodate this enormous amount of data.
The demand to store ever-increasing volumes of information has resulted in the widespread implementation of data centers for Big Data. These centers consume massive amounts of energy (about 3% of global electricity supply) and rely on magnetization-based hard disk drives with limited storage capacity (up to 2 TB per disk) and lifespan (up to 3-5 years). Laser-enabled optical data storage is a promising and cost-effective alternative for meeting this unprecedented demand. However, the diffractive nature of light has limited the size of the information bits that can be reached and, as a result, the storage capacity of the optical disks.
Researchers at USST, RMIT and NUS have now overcome this limitation by using earth-rich lanthanide-doped upconversion nanoparticles and graphene oxide flakes. This unique material platform enables low-power optical writing nanoscale information bits (nanoscale refers to sizes of 1–100 nanometers, where one nanometer is one billionth of a meter).
A much-improved data density can be achieved for an estimated storage capacity of 700 TB on a 12-cm optical disk, comparable to a storage capacity of 28,000 Blu-ray disks. Furthermore, the technology uses inexpensive continuous-wave lasers, reducing operating costs compared to traditional optical writing techniques using expensive and bulky pulsed lasers.
This technology also offers the potential for optical lithography of nanostructures in carbon based chips that are highly required in next-generation nanophotonic devices.
The impact
Optical data storage has advanced remarkably over the last decades, but the optical disk storage capacity is still limited to a few Terabytes.
The developed sub-diffraction optical writing technology can produce an optical disk with the largest storage capacity of all available optical devices.
While advances are needed to optimize the technology, the results open new avenues to address the global challenge of data storage. The technology is suited to the mass production of optical disks, so that the potential is enormous.
This ground-breaking technology could offer a cheaper and sustainable solution for the next generation of high-capacity optical data storage while enabling the energy-efficient nanofabrication of flexible graphene based electronics.
How it works
The technology uses a new nanocomposite material that combines graphene oxide flakes with upconversion nanoparticles.
Graphene oxide can be seen as a single layer of graphite with different oxygen groups. Reducing graphene oxide by eliminating these oxygen groups produces a material called reduced graphene oxide, which has similar properties to graphene.

Sub-diffraction information bits have been written in the nanocomposite using upconversion nanoparticles to reduce graphene oxide locally upon engineered illumination. The reduction of graphene oxide was induced by high-energy quanta generated in the excited upconversion nanoparticles through a process of resonance energy transfer.
The researchers chose upconversion nanoparticles because they enable efficient sub-diffraction optical writing using low laser beam intensity, resulting in low energy consumption and long lifetime of optical devices.
The team
The research was led by Distinguished Professor Min Gu at the Centre for Artificial-Intelligence Nanophotonics, USST and RMIT University, in collaboration with Professor Xiaogang Liu at the Department of Chemistry, NUS and the N.1 Institute for Health, NUS. The experimental work was led by Dr Simone Lamon, Postdoctoral Research Fellow at USST School of Optical-Electrical and Computer Engineering and RMIT School of Science.
The paper, “Nanoscale optical writing through upconversion resonance energy transfer” is published in Science Advances on Feb. 24, 2021.