Dual-Channel Binary Gray-Image Display Enabled with Malus-Assisted Metasurfaces

Metasurfaces composed of anisotropic nanostructures possess the ability to manipulate the polarization and intensity of light simultaneously, which paves an emerging way to construct multiplexing metadevices capable of displaying gray images with high resolution and reliability. However, previous multiplexing metadevices for gray-image displaying are mostly based on nanostructures with varied geometries and/or supercell design strategies, which complicate both the metasurface design and manufacturing or decrease the information resolution. Here, benefiting from the orientation degeneracy implied in Malus’s law, we show that gray-image multiplexing can be implemented simply by a single-sized nanostructure-design approach. Specifically, by configuring the four-step orientations of silver nanobricks, two independent information channels can be established to store different gray images into a single metasurface. We experimentally demonstrate the Malus-assisted metasurface, which functions as a dual-channel gray-image display device to record two independent binary gray images without crosstalk. With the single-sized design strategy, each nanobrick can record information of two channels, and the proposed metasurface simultaneously owns an ultrahigh information density of 84 667 dots per inch for both of the two gray images. With advantages such as simplicity in nanostructure design, ultracompactness, high resolution, broadband working windows, and high security, the proposed metasurfaces empower advanced researches and applications in anticounterfeiting, information hiding, information multiplexing, ultracompact image displaying, high-density optical storage, integrated and multiplexed nanooptoelectronics, etc.

Figure 1

Principle of the dual-channel gray-image display based on a Malus-assisted metasurface. (a) Simplified nonorthogonal polarization optical path composed of a bulk-optic polarizer, a nanopolarizer, and an analyzer. (b) Details of nanopolarizers with four different orientation candidates for dual-channel binary-intensity manipulations. The nanopolarizers operate under channel 1 when (α₁, α₂) = (−22.5°, 22.5°) while under channel 2 when that is (22.5°, 67.5°). The green, red, and blue arrows in the polarization profiles denote the transmission axis directions of the bulk-optic polarizer, the nanopolarizers, and the analyzer, respectively. The intensity profiles indicate the binary-intensity manipulations of nanopolarizers under two channels. (c) Operation schematic of the dual-channel gray-image display based on a single-size Malus-assisted metasurface. A 50 × objective is used to enlarge the gray images, and a narrow-band source of 633 nm is employed for illumination.

Figure 2

Target patterns and experimentally captured images of the Malus-assisted metasurface in the transmission operating mode. (a)–(d) Target patterns and (e)–(l) the corresponding experimentally captured images of the dual-channel multiplexing metasurface. All experimental images are captured by the same optical microscope. (e)–(h) and (i)–(l) show the captured micrographs with a narrow-band filter of 633 nm and without the filter, respectively. Transmission axis directions of the polarizer and analyzer in all cases are denoted by the green and blue arrows, respectively. Scale bars of 20 µm are denoted in all experimental images.

Figure 3

Experimentally captured images for the dual-channel multiplexing metasurface in the reflection operating mode by using the same optical microscope like Fig. 2, observed by inserting a red filter (a)–(d) and without any color filter (e)–(h). Scale bars of 20 µm are denoted in all images.

Figure 4

Experimentally captured images of QR code patterns in the transmission operating mode. (a)–(f) Experimentally captured images under polarization optical paths with different polarization-state combinations. All transmission axis directions of the polarizer and the analyzer are denoted by green and blue arrows, respectively. (g) Experimentally captured images under an unpolarized optical path without the polarizer and the analyzer. A narrow-band filter (633 nm) is inserted into the optical system and all experimental results are optical micrographs with a 50 × objective. Scale bars of 20 µm are shown in all images.

Figure 5

Design of the single-size Malus-assisted metasurfaces. (a) Illustration of the nanobrick unit cell of a Malus-assisted metasurface. The unit cell is composed of a planar silica substrate and a silver nanobrick. The orientation angle of the nanobrick is denoted by φ. (b) Simulated reflectivities (R_l, R_s) and transmissivities (T_l, T_s) versus wavelength.

Figure 6

SEM image of the fabricated metasurface sample (partial view).