Next generation of optical data storage technology towards Big Data: how to store a data bit within the space smaller than a photon with optical super-resolution techniques

That storing, accessing and sharing data generated during diverse human activities has been a hot topic in the era of information. Digital signals produced during the communications between machines, biogenetic data that records the beauty of life, atmospheric forecast that tells the weather, blossoms of information boosted our modernization yet the great informational revolution also brings about a new ‘crisis’. In accordance with a recent report, data produced in global range is estimated to reach as much as 175 ZB (which is equivalent to 175,000,000,000 TB) by 2025, which would be a great challenge for data-storage methodology and technology.
    Back in 1980s, conventional commercial optical storage technology is used to take superiority on its merits of high storing capacity, low energy consumption for about two decades, whereas the inevitable diffraction barrier confines the smallest size of one data bit in regime of light wavelength scale, which induces finite capacity (~GB scale) of conventional optical discs and far from the demand in contemporary data storage. Thus, breaking down the physical constraint and packing up more information in one single disc to elevate storing capacity from GB scale to TB or even PB scale is the key for settling the coming crisis of data storage. Lately, Prof. Cao Yaoyu and Prof. Li Xiangping et al. from Institute of Photonic Technology, Jinan University reviewed the super-resolution data storage techniques with ‘Research progress of super-resolution optical data storage’. The review summarizes fundamentals and principles of advanced super-resolution data storage techniques and introduces current progress in regions of both near-field 2D and far-field 3D high-capacity optical storing techniques.
    On account of the diffraction limit, the size of one single data bit recorded via conventional optical storage techniques could ever reach is in about half of wavelength scale. Yet the Stimulated Emission Depletion (STED) microscopy proposed by Stefan. W. Hell in 1994 inspires a new direct laser writing approach of utilizing the nature in one optically saturated process to bypass the diffraction barrier. Simultaneously adapting a Gaussian excitation laser beam and a depletion beam, novel optical two-beam lithography methods have been developed. In 2013, Prof. Gan Zongsong, Prof. Cao Yaoyu and their colleagues achieved finest lateral double-line resolution of 52 nm and realized the fabrication of dangling nanowire with feature size down to 9 nm. In 2015, Prof. Li Xiangping and Prof. Cao Yaoyu et al. combined the concept of dual-beam super-resolution with multifocal array technique and successfully recorded data bits with size down to 33 nm. Meanwhile, solution to recording data in a rate of ~Gb/s was suggested and verified (as demonstrated in Figure 1) , which brings light to the issue of storing capacity, recording rate and energy consumption. In addition, two-photon absorption (TPA) storage technique based 3D far-field super-resolution optical storage, 2D near-field super-resolution techniques like scanning probe storage technique solid-state immersed lens storage technique and super-resolution near-field structural storage technique are also involved (Figure 2). At the end of the review, the remaining dark clouds that linger over super-resolution optical storage techniques and the prospect on the future would be discussed and concluded.

Fig. 1  Parallelized super-resolution data storage technique for ultrahigh capatcity and ultrafast optical recording

Fig. 2  Development of super-resolution optical data storage techniques

About team
The Nanophotonic devices researching group, Institute of Photonic Technology, Jinan University have been committed to developing advanced photonic technology including laser nanofabrication technique, super-resolution imaging and optical storage techniques, meta-materials and surface plasmonic technique, etc. Remarkably, by developing dual-beam super-resolution optical storage technology, Prof. Li Xiangping, Prof. Cao Yaoyu and their collaborators unprecedentedly realized the fabrication of ultrasmall recording bit with size of 33 nm, lifting the theoretical storing density of optical storage for over ten-thousand folds. At present, the research group is comprised of 11 teachers (including 2 professors/researchers, 5 associate professors/researchers), 4 postdoctoral researchers and over 20 graduate students. Up to date, more than 30 peer-reviewed papers has been published in several internationally acclaimed journals including Science, Light Science & Applications, Nano Letters, ACS Nano, etc. So far, the group is equipped with ultra-clean laboratory and advanced femto-second laser fabricating systems and electron beam fabricating facilities, providing robust backbone for their advancing researches.

Jiang Meiling, Zhang Mingsi, Li Xiangping, et al. Research progress of super-resolution optical data storage[J]. Opto-Electronic Engineering, 2019, 46(3): 180649.