Dual-encryption freedom via a monolayer-nanotextured Janus metasurface in the broadband visible

Monolayer directional metasurface for all-optical image classifier doublet

Diffractive deep neural networks, known for their passivity, high scalability, and high efficiency, offer great potential in holographic imaging, target recognition, and object classification. However, previous endeavors have been hampered by spatial size and alignment. To address these issues, this study introduces a monolayer directional metasurface, aimed at reducing spatial constraints and mitigating alignment issues. Utilizing this methodology, we use MNIST datasets to train diffractive deep neural networks and realize digital classification, revealing that the metasurface can achieve excellent digital image classification results, and the classification accuracy of ideal phase mask plates and metasurface for phase-only modulation can reach 84.73% and 84.85%, respectively. Despite a certain loss of degrees of freedom compared to multi-layer phase mask plates, the single-layer metasurface is easier to fabricate and align, thereby improving spatial utilization efficiency.

9-bit spin- and wavelength-encoded hologram using a hybrid metasurface

Metasurface holographic encryption, with high resolution and strong concealment, is promising for information security. However, traditional metasurface holographic encryption is limited by spin-polarization channels and monochromaticity, restricting the level of security and information capacity. In this Letter, we propose a 9-bit spin- and wavelength-encoded hologram achieved by encoding phase and amplitude information into full spin polarization and primary color channels using a hybrid metasurface. Our hybrid metasurface structure can break the limitations of traditional metasurfaces, significantly increasing the number of encoded channels by an order of magnitude. We believe that this strategy can provide a new, to the best of our knowledge, approach to high-capacity information encoding and encryption.

Directionally duplexed all-dielectric metalens for multifunctional structured light generation

Directionally duplexed metalenses manipulated by the geometric phase of a silicon nano-bar are theoretically designed to generate multifunctional structured light. It is numerically demonstrated that incident light with different linear and circular polarization states, along forward and backward propagation directions, can be differentially converted into multiple focusing structured beams of arbitrary topological charges, either of vector light with azimuthally variant polarizations or of vortex light with helical phases. Due to the all-silicon and nonresonant metastructural design, the resultant high working efficiencies of our proposed metalens are promising for applications such as optical communication, nanoparticle manipulation, and other direction-duplexed multifunctional optical meta-devices.

On-chip asymmetric beam-steering for broadband visible light

Artificial optical nanostructures including three-dimensional (3D) metamaterials and two-dimensional (2D) metasurfaces have shown overwhelming capability to control electromagnetic waves in desirable manners. However, the challenges of manufacturing a complex 3D bulk architecture or achieving nanoscale alignment between multilayers limit their practical applications, and they are unable to be used in on-chip integrated photonic devices. Therefore, the emerging dimensionality-reduction to on-chip metadevices would be of promising research value. Here, we propose a visible-frequency on-chip dual-layer design by cascading one-dimensional (1D) plasmonic metawires with metagratings, which can effectively manipulate surface plasmon polariton (SPP) wavefronts and exhibit on-chip asymmetric beam-steering functionality. Our 1D metawires consist of trapezoidal plasmonic nanoantennas and can enable broadband (460-700 nm) on-chip beam-deflection with a high conversion efficiency. The cascading plasmonic coupling between metawires/metagrating is further demonstrated with broadband asymmetric propagation performance, which is crucial for on-chip plasmonic device development. Finally, we study and theoretically verify a cascade system that integrates a dual-functional (convergent/divergent) lens for the forward/backward propagation, respectively. Compared with conventional free-space multilayer metasurfaces, on-chip 1D metawires enjoy single-time lithography processing and no alignment requirement for implementation in multifunctional devices. We believe that the proof-of-concept on-chip metawires study will pave a new, to the best of our knowledge, way for creating multifunctional photonic integrated devices and hold tremendous potential in realizing on-chip transformation optics, information processing, spectrometers, as well as optical sensors.