The current nanofabrication techniques including electron beam lithography provide fabrication resolution in the nanometre range. The major limitation of these techniques is their incapability of arbitrary three-dimensional nanofabrication. This has stimulated the rapid development of far-field three-dimensional optical beam lithography where a laser beam is focused for maskless direct writing. However, the diffraction nature of light is a barrier for achieving nanometre feature and resolution in optical beam lithography. Here we report on three-dimensional optical beam lithography with 9 nm feature size and 52 nm two-line resolution in a newly developed two-photon absorption resin with high mechanical strength. The revealed dependence of the feature size and the two-line resolution confirms that they can reach deep sub-diffraction scale but are limited by the mechanical strength of the new resin. Our result has paved the way towards portable three-dimensional maskless laser direct writing with resolution fully comparable to electron beam lithography.

The emerging metasurfaces with the exceptional capability of manipulating an arbitrary wavefront have revived the holography with unprecedented prospects. However, most of the reported metaholograms suffer from limited polarization controls for a restrained bandwidth in addition to their complicated meta-atom designs with spatially variant dimensions. Here, we demonstrate a new concept of vectorial holography based on diatomic metasurfaces consisting of metamolecules formed by two orthogonal meta-atoms. On the basis of a simply linear relationship between phase and polarization modulations with displacements and orientations of identical meta-atoms, active diffraction of multiple polarization states and reconstruction of holographic images are simultaneously achieved, which is robust against both incident angles and wavelengths. Leveraging this appealing feature, broadband vectorial holographic images with spatially varying polarization states and dual-way polarization switching functionalities have been demonstrated, suggesting a new route to achromatic diffractive elements, polarization optics, and ultrasecure anticounterfeiting.

The advance of nanophotonics has provided a variety of avenues for light-matter interaction at the nanometer scale through the enriched mechanisms for physical and chemical reactions induced by nanometer-confined optical probes in nanocomposite materials. These emerging nanophotonic devices and materials have enabled researchers to develop disruptive methods of tremendously increasing the storage capacity of current optical memory. In this paper, we present a review of the recent advancements in nanophotonics-enabled optical storage techniques. Particularly, we offer our perspective of using them as optical storage arrays for next-generation exabyte data centers.

Phase, polarization, amplitude, and frequency represent the basic dimensions of light, playing crucial roles for both fundamental light-material interactions and all major optical applications. Metasurfaces have emerged as a compact platform to manipulate these knobs, but previous metasurfaces have limited flexibility to simultaneous control them. A multi-freedom metasurface that can simultaneously and independently modulate phase, polarization, and amplitude in an analytical form is introduced, and frequency multiplexing is further realized by a k-space engineering technique. The multi-freedom metasurface seamlessly combines geometric Pancharatnam-Berry phase and detour phase, both of which are frequency independent. As a result, it allows complex-amplitude vectorial hologram at various frequencies based on the same design strategy, without sophisticated nanostructure searching of massive geometric parameters. Based on this principle, full-color complexamplitude vectorial meta-holograms in the visible are experimentally demonstrated with a metal-insulator-metal architecture, unlocking the longsought full potential of advanced light field manipulation through ultrathin metasurfaces.functional layers, emerge as a desirable platform to manipulate the light field at will with large control and flexibility. [3][4][5][6][7] Exciting applications have already been demonstrated on the metasurface platform, including flat diffractive and polarization optical components, much more compact and lightweight than conventional bulky counterparts. By engineering the scattering properties of the individual metaelements constituting the metasurface to mold the geometric phase, resonant phase or propagation phase, we are able to control phase, [8,9] amplitude, [10,11] polarization, [12,13] or frequency [14][15][16] of light, leading to high-efficiency metalenses, [9] high-fidelity holograms, [8] broadband polarization components, [12,17] and highperformance biosensors. [15] However, these ultrathin components tend to focus on single-dimensional light manipulation, controlling either the local phase, or amplitude, or polarization, or frequency, at a time, inherently limiting potential opportunities. For example, metasurface holograms and metalenses based on resonant phase and propagation phase are typically limited to a narrow range of frequencies. [18,19] Geometric Pancharatnam-Berry (P-B) phase metasurfaces operate over broader bandwidths, but they are restricted to circular polarization only. [8] To improve the performance and enrich the functionality of metasurfaces for a broader range of applications, independent

The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths. The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application, in addition to high fabrication precision demands. Utilizing a different design principle, we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances (near-grazing incidence) in the visible–near-infrared regime. By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters, the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle. The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand, thereby opening new routes for flat optics with high performances and improved practicality.