Fig. 1. 200-layer 3D optical storage based on two-photon absorption^[11]. (a) Experimental system used for data recording; (b) confocal scanning results in xy and xz directions

Fig. 2. Examples of four-dimensional optical storage. (a) Recording of three kinds of pattern “X”, “Y”, and “Z” in the same portion^[15] (polarization angles of the recording beam are 0°, 60°, and 120°, respectively); (b) erasure of 3×3 lattices at the center with the horizontal polarization light, then rewrite with the vertical polarization light^[15]; (c) three-layer data storage with two polarization states achieved using two-photon absorption, where the letters “I” and “J” encoded in the same region in the second layer are completely erased and rewritten as letters “F” and “E”^[16]; (d) ultrafast laser-induced liquid nanophase separation in the Br^-and I^- doped glass^[19]; (e) multicolor patterns are generated in the glass by adjusting parameters during writing^[19]

Fig. 3. Multidimensional optical storage based on surface plasmon in gold nanorods. (a) Photothermal reshaping of gold nanorods through polarization and wavelength selective absorption^[21]; (b) 18 images stored in the same area using three different laser wavelengths and two laser polarization states^[21]; (c) schematic of OAM-based six-dimensional optical storage encoding and decoding^[25]

Fig. 4. Five-dimensional (5D) optical storage based on nanogratings. (a) Scanning electron microscopy (SEM) images of nanostructures under different pulse numbers^[26]; (b) schematic of data recording setup^[29]; (c) 100-layer error-free 5D optical storage^[37]

Fig. 5. Far-field superresolution optical storage technology. (a) Realizing superresolution optical storage using the pupil-plane filter^[45]; (b) superresolution recording by focusing radially polarized beams with a annular objective lens, where γ=d1/d2 is defined as the ratio of inner to outer radii^[47]; (c) relationship between the maximum capacity of a single disk and the feature size of the recorded bits, where the inset illustrates the principle underlying SPIN’s ability to achieve superresolution recording^[2]; (d) feature size of free-standing lines varies with the intensity of the inhibition beam, with a minimum value of 9 nm^[53]

Fig. 6. Using rsEGFP to achieve superresolution optical storage^[54]. (a) Diagram of optical writing steps; (b) experimental recording results

Fig. 7. Superresolution parallel reading and writing systems. (a) 3D parallelized recording through a volumetric superresolved multifocal array generated by SLM^[55]; (b) multibeam parallel superresolution laser direct writing system based on rotary mirror scanning^[56-58]

Fig. 8. Using elastic substrates to reduce pixel pitch in dual-beam superresolution storage^[61]. (a) Schematic diagram of writing on pre-stretched PDMS substrate; (b) SEM image of pixel pitch array on PDMS substrate with 30% stretching ratio; (c) SEM images of pixel pitch array on normal PDMS substrate; (d) a leaf-shape nanodot pattern with average pixel spacing of 96 nm and single-dot size of 34 nm

Fig. 9. Dual-beam superresolution technology based on upconversion resonance energy transfer (RET)^[62]. (a) Principle of nanoscale optical storage, where 980 nm writing beam induces GO reduction through RET of high-energy quanta from UCNPs, while the 808 nm inhibition beam inhibits GO reduction through suppression of high-energy quantum generation in UCNPs; (b) readout results without (left) and with (right) inhibition beam; (c) intensity profiles along the dashed lines in the insets of (b)

Fig. 10. Ultra-high density optical storage based on AIE-doped polymer ^[64-66]. (a) Change of fluorescence intensity of TPE with water content, where the percentage in the picture represents the water content^[64]; (b) TPE solid state thin film under UV lamp irradiation^[64]; (c) readout result of nine layers, with a spacing of 1.5 μm between adjacent points and an interval of 2 μm between different layers^[65];(d) writing and reading principle of superresolution 3D disk based on AIE-DDPR, where the illustration shows the readout results of 100 layers, and the minimum spot size and the lateral distance between two adjacent spots are 54 nm and 70 nm, respectively^[66];(e) the storage capacity of a single superresolution 3D disk is approximately equivalent to that of a petabit-level blu-ray library or an HDD data array^[66]