Opportunity
The information community has a growing need to diversify information storage and enhance the security and capacity of encrypted information. Metasurfaces, as ultra-compact optical devices, offer significant potential for image display and storage due to their sub-wavelength pixel control and precise light manipulation. A fundamental goal in metasurface imaging is the integration of printing images and holographic images, which requires independent control over the amplitude and phase of incident light. Existing methods to integrate multiple holographic images with a printing image, such as wavelength multiplexing, coherent pixel design, or combining Pancharatnam-Berry (PB) phase and propagation phase, face inherent limitations. Wavelength multiplexing, while simple, often suffers from intensity imbalance among different color channels due to variations in transmission efficiency and spectral crosstalk within multiplexing pixels, which is exacerbated by nano-fabrication tolerances. These issues degrade image quality and create efficiency disparities, hindering the realization of high-quality, high-capacity, and secure optical information encryption and storage devices.
Technology
This patent discloses a metasurface structure and method designed to integrate a multi-color optical-printing image with multiple encrypted monochromatic holographic images in a single device, addressing the limitations of prior art. The core innovation is the use of a plurality of sub-wavelength structures, such as silicon nano-blocks arranged in a monolayer on a substrate. These nano-blocks are engineered with specific dimensions (e.g., varying lengths) to exhibit different chromatic responses, enabling them to transmit specific colors (e.g., red, green, blue, yellow) under white light illumination, thereby forming a multi-color printing image for camouflage. Crucially, the same nano-blocks are also rotated to impart specific Pancharatnam-Berry (PB) phases. Using an optimized Gerchberg-Saxton (G-S) algorithm, the phase distributions required to generate multiple holographic images are calculated and encoded into the orientation of these nanostructures. A key technological advancement is the concept of "unevenly distributed pixels" (UEDP), where the metasurface is composed of super-pixel regions with different nano-block sizes, filling densities, and arrangements (e.g., an RGB region and monochromatic regions with different pixel periods). This UEDP design minimizes spectral crosstalk between color channels and balances the transmission intensities of different colored holograms by adaptively compensating for efficiency variations (e.g., enlarging the area of less efficient blue channels). The holographic images are decrypted only when the metasurface is illuminated with a specific laser possessing a precise combination of wavelength, polarization, spatial angle, and focal distance, with each hologram requiring a unique key.
Advantages
- Integrates a multi-color printing image (camouflage) with multiple independent monochromatic holographic images (encrypted data) into a single, ultra-thin monolayer device.
- The "unevenly distributed pixels" (UEDP) design effectively minimizes spectral crosstalk between different color channels, improving holographic image quality and color purity.
- Balances the intensity and efficiency among different colored holographic channels, overcoming inherent material transmission limitations.
- Provides high-security encryption through multi-parameter keys: each hologram requires a unique combination of wavelength, polarization, spatial observation angle, and focal distance for decryption.
- Offers high information storage capacity by multiplexing multiple independent images (one printing + several holograms) in one device.
- Utilizes a PB phase design, enabling precise wavefront control with high efficiency and simplified fabrication through nano-block rotation rather than complex 3D shaping.
- The camouflage printing image under white light provides a deceptive layer, enhancing anti-counterfeiting and security.
Applications
- High-security anti-counterfeiting labels and tags for products, currency, and official documents.
- Secure packaging where the printing image shows a brand logo (camouflage) and holograms contain authentication information.
- Compact optical data storage and encryption devices.
- Information multiplexing platforms for steganography and cryptography.
- Advanced optical components for displays, augmented/virtual reality (AR/VR), and optical computing.
- Educational or demonstration tools for optics and photonics.
