An all-dielectric optical antenna supporting Mie resonances enables light confinement below the free-space diffraction limit. The Mie scattering wavelengths of the antenna depend on the structural geometry, which allows the antennas to be used for colored imprint images. However, there is still room for improving the spatial resolution, and new polarization-dependent color functionalities are highly desirable for realizing a wider color-tuning range. Here, we show all-dielectric color printing by means of dual-color pixels with a subwavelength-scale resolution. The simple nanostructures fabricated with monocrystalline silicon exhibit various brilliant reflection color by tuning the physical dimensions of each antenna. The designed nanostructures possess polarization-dependent properties that make it possible to create overlaid color images. The pixels will generate individual color even if operating as a single element, resulting in the achievement of subwavelength-resolution encoding without color mixing. This printing strategy could be used to further extend the degree of freedom in structural color design.

Mie resonance wavelengths of a dielectric structure are strongly dependent on the inherent material property and structural geometry. In particular, a high-index nanostructure enables light confinement within itself over the range of visible wavelengths, which allows the Mie resonator to be applied to a pixel in color printing of subwavelength-scale resolution. However, if the Mie resonator is packed into a smaller area in order to achieve better resolution, the interaction between adjacent resonators occurs depending on these spatial distances, leading to unexpected color changes. Here, we demonstrate metal-masked Mie-resonant color printing for suppressing undesirable color changes. We observed that the interaction between monocrystalline Si resonators can be suppressed by the addition of a Cr mask. The pixels with this functionality can produce individual colors even if operating as a single element or in other periodic arrays, resulting in the realization of higher resolution encoding. The coincidence of resonance peak positions derived from excited electric/magnetic dipoles enables the demonstration of brilliant full-color printing with higher color purity. Furthermore, a vivid printing image with a resolution of more than 100 000 dpi was achieved using the designed subwavelength pixels. This study can contribute not only to the improvement of the resolution of color printing but also to the suppression of unwanted interactions of Mie resonance in optical devices.

All-dielectric color printing by means of high-index Mie resonators has enabled wider control of reflection colors depending on structural geometry. However, modifying the geometry, including the height, by using conventional fabrication processes remains challenging, and drastic color modification approaches via the addition of a new tuning axis are required to extend color varieties and applications. Here, we demonstrate all-dielectric pixel color control through Si oxidation. Oxidized monocrystalline Si nanostructures exhibit wider tunability of brilliant reflection colors depending on the oxidation reaction. The different color change properties of each nanostructure enable the construction of an "invisible ink" that can hide color information. This approach for controlling printing color could be utilized to further extend color variation and reactive applications.

Silicon photonics have attracted significant interest because of their potential in integrated photonics components and all-dielectric meta-optics elements. One major challenge is to achieve active control via strong photon–photon interactions, i.e. optical nonlinearity, which is intrinsically weak in silicon. To boost the nonlinear response, practical applications rely on resonant structures such as microring resonators or photonic crystals. Nevertheless, their typical footprints are larger than 10 μm. Here, we show that 100 nm silicon nano-resonators exhibit a giant photothermal nonlinearity, yielding 90% reversible and repeatable modulation from linear scattering response at low excitation intensities. The equivalent nonlinear index is five-orders larger compared with bulk, based on Mie resonance enhanced absorption and high-efficiency heating in thermally isolated nanostructures. Furthermore, the nanoscale thermal relaxation time reaches nanosecond. This large and fast nonlinearity leads to potential applications for GHz all-optical control at the nanoscale and super-resolution imaging of silicon.

We present an experimental demonstration of nanoscale gap plasmon resonators that consist of an individual suspended plasmonic nanowire (NW) over a metallic substrate. Our study demonstrates that the NW supports strong gap plasmon resonances of various gap sizes including single-nanometer-scale gaps. The obtained resonance features agree well with intuitive resonance models for near- and far-field regimes. We also illustrate that our suspended NW geometry is capable of constructing plasmonic coupled systems dominated by quasi-electrostatics.