Research progress of super-resolution optical data storage

Overview: With the rapid development of Big Data and artificial intelligence, emerging information technologies such as Smartphone, Internet of Things, Biogenetic Data, Atmosphere, and Geographic Information compel dramatically increasing demands on extremely high information storage capacity and speed. At present, data storage and archiving methods mainly rely on conventional magnetization-based information storage method which generally suffers from technique challenges raised by short lifetime and high energy consumption. Optical data storage technology, in comparison, is well known for its advantages of high storage capacity, low energy consumption, and high security. However, the disc capacity of optical data storage technology inevitably gets stuck in the physical fundamental barrier-optical diffraction limit. The diffraction limit of light is substantially introduced by the lack of spatial frequencies higher than that can be supported by certain light wave and optical system. As a consequence, light spot cannot be infinitely squeezed down to a mathematically ideal point, giving rise to limited density and capacity of optical data storage. How to crash through optical diffraction barrier and improve resolution of optical storage system, thereby increasing the data storage capacity of the optical storage system is the key to incorporating optical storage technology with information technology trend such as big data and cloud computing. In this review, we have introduced the principle of contemporary optical storage techniques capable of storing and retrieving data in a manner of being beyond the diffraction-limit and recent progress in ultra-high capacity optical data storage techniques, including far field super-resolution three dimensional (3D) optical storage techniques and near field super-resolution two dimensional (2D) optical storage techniques. The far field super-resolution is the technique can reduce the full width at half maximum (FWHM) of the intensity distribution of the focused spot in the far field. The main techniques of far field super-resolution optical storage are based on nonlinear interaction between light and recording medium, such as two-photon absorption-based process and saturation stimulated emission depletion fluorescence-inspired approaches. The near field super-resolution is the technique that mainly utilize the evanescent wave within the sub-wavelength distance between the light source and the recording medium. The main techniques of near field super-resolution optical storage involve near field scanning probe methods, solid immersion lens approaches, and super-resolution near-field structure methods. Eventually, the here-and-now problems confronted by the super-resolution optical data storage and future development of optical storage technology towards ultra-high capacity optical disc based on optical super-resolution techniques are discussed.