Optical metasurfaces can offer high-quality multichannel displays by modulating different degrees of freedom of light, demonstrating great potential in the next generation of optical encryption and anti-counterfeiting. Different from the direct imaging modality of metasurfaces, single-pixel imaging (SPI) as a typical computational imaging technique obtains the object image from a decryption-like computational process. Here, we propose an optical encryption scheme by introducing metasurface-images (meta-images) into the encoding and decoding processes as the keys of SPI encryption. Different high-quality meta-images generated by a dual-channel Malus metasurface play the role of keys to encode multiple target images and retrieve them following the principle of SPI. Our work eliminates the conventional digital transmission process of keys in SPI encryption, enables the reusability of a single metasurface in different encryption processes, and thereby paves the way toward a high-security optical encryption between direct and indirect imaging methods.

By virtue of the extraordinary capability of manipulating the polarization state, amplitude and phase of electromagnetic fields, metasurfaces can be employed to display holographic or nanoprinting images with unprecedented spatial resolution. Bringing holography and nanoprinting together is an effective way toward information multiplexing. However, current approaches mostly utilize interleaving or stacking nanostructures with different functionalities to construct multiplexed metasurfaces, hence they are equivalent to a combination of several metasurfaces and the information capacity of each metasurface remains unchanged. Here, by combining intensity modulation governed by Malus's law with phase manipulation based on both geometric and propagation phases, a single‐cell‐designed metasurface for three‐channel image displays is proposed. The new design strategy can significantly improve the information capacity since the extra phase modulation originates from the orientation degeneracy and dimension variation of nanostructures rather than multilayer or interleaving design. Specifically, a three‐channel metasurface is experimentally demonstrated, which can simultaneously record a continuous grayscale nanoprinting image in the near field and project two independent holographic images in the far field. With the advantages of crosstalk‐free and ultracompactness, the proposed three‐channel metasurfaces can empower the design of multifunctional nano‐optical elements for applications in image displays, optical anticounterfeiting, optical storage and many other related fields.

With the rapid progress in computer science, including artificial intelligence, big data and cloud computing, full-space spot generation can be pivotal to many practical applications, such as facial recognition, motion detection, augmented reality, etc. These opportunities may be achieved by using diffractive optical elements (DOEs) or light detection and ranging (LIDAR). However, DOEs suffer from intrinsic limitations, such as demanding depth-controlled fabrication techniques, large thicknesses (more than the wavelength), Lambertian operation only in half space, etc. LIDAR nevertheless relies on complex and bulky scanning systems, which hinders the miniaturization of the spot generator. Here, inspired by a Lambertian scatterer, we report a Hermitian-conjugate metasurface scrambling the incident light to a cloud of random points in full space with compressed information density, functioning in both transmission and reflection spaces. Over 4044 random spots are experimentally observed in the entire space, covering angles at nearly 90°. Our scrambling metasurface is made of amorphous silicon with a uniform subwavelength height, a nearly continuous phase coverage, a lightweight, flexible design, and low-heat dissipation. Thus, it may be mass produced by and integrated into existing semiconductor foundry designs. Our work opens important directions for emerging 3D recognition sensors, such as motion sensing, facial recognition, and other applications.

Metasurfaces capable of controlling more than two types of optical properties have drawn a broad interest recently, as they can bring great flexibility and possibilities to the design of highly-integrated multifunctional devices such as simultaneous nanoprint and holograms. However, current multifunctional metasurfaces can perform only two types of optical manipulations separately. Furthermore, their supercell or multilayer design strategies would complicate both the nanostructure design and manufacturing, and are difficult to implement the miniaturization, low-cost, and multifunctionality of light integration. Herein, merely with a single-cell design approach, a tri-functional metasurface enabled with triple manipulations of light is proposed. By merging the spectrum, polarization and phase manipulations into a single metasurface, a "three-in-one" meta-device simultaneously acting as a structural-color nanoprint, a polarization-controlled grayscale meta-image displayer and a phase-modulated meta-hologram can be constructed. Specifically, the structural-color image appears right at the metasurface plane under a natural light source while the grayscale meta-image and holographic image are reconstructed by taking different optical setups as decoding keys, which can not only significantly increase the light integration but also improve the reliability of both images. The proposed metasurface represents a new paradigm in designing multifunctional meta-devices, and has promising prospects in image displays, optical storage, optical anti-counterfeiting, etc.

Interference usually occurs between two non-orthogonally polarized light beams. Hence, metasurface enabled polarization multiplexing is generally conducted under two orthogonal polarization states to realize independent intensity and/or phase modulations. Herein, we show that polarization multiplexed metasurfaces can work under three non-orthogonal polarization states to realize tri-channel image displays with independent information encoding. Specifically, enabled by orientation degeneracy, each nanostructure of the metasurface operates with triple-manipulations of light, i.e., two channels for independent intensity manipulation under π/4 and 3π/8 linearly polarized (LP) light, respectively, and one channel for phase manipulation without polarization control. We experimentally demonstrate this concept by recording one continuous-brightness polychromatic image and one binary-brightness polychromatic image right at the metasurface plane, while a continuous-brightness polychromatic image is reconstructed in the far field, corresponding to three independent channels, respectively. More interestingly, in another design strategy with separated image encoding of two wavelengths, up to six independent image-display channels can be established and information delivery becomes safer by utilizing encryption algorithms. With the features of high information capacity and high security, the proposed meta-devices can empower advanced research and applications in multi-channel image displays, orbital angular momentum multiplexing communication, information encryption, anti-counterfeiting, multifunctional integrated nano-optoelectronics, etc.