Optical secret sharing with cascaded metasurface holography (2110.03265v1)

Abstract: Secret sharing is a well-established cryptographic primitive for storing highly sensitive information like encryption keys for encoded data. It describes the problem of splitting a secret into different shares, without revealing any information about the secret to its shareholders. Here, we demonstrate an all-optical solution for secret sharing based on metasurface holography. In our concept, metasurface holograms are used as spatially separable shares that carry an encrypted message in form of a holographic image. Two of these shares can be recombined by bringing them close together. Light passing through this stack of metasurfaces accumulates the phase shift of both holograms and can optically reconstruct the secret with high fidelity. On the other hand, the holograms generated by the single metasurfaces can be used for identifying each shareholder. Furthermore, we demonstrate that the inherent translational alignment sensitivity between the two stacked metasurface holograms can be used for spatial multiplexing, which can be further extended to realize optical rulers.

• The paper introduces a novel optical secret sharing scheme using cascaded metasurface holography, where individual optical shares combine to reconstruct a hidden secret image.
• Cascading two specific metasurfaces at 100 µm distance is shown to generate a unique holographic image of the secret, which neither metasurface produces alone.
• Translational multiplexing, using in-plane alignment, adds another dimension for multiplexing holographic images, illustrating potential for high-resolution optical rulers and scalability.

Optical Secret Sharing with Cascaded Metasurface Holography

In the paper of optical secret sharing through cascaded metasurface holography, the authors present an intriguing approach to cryptography leveraging advanced optical techniques. This work explores secret sharing, a cryptographic primitive originally developed by Adi Shamir and George Blakley, using physical rather than digital means. Specifically, the research makes use of metasurface holography—a versatile mechanism capable of dense information storage with strong encryption potential.

Key Contributions

Central to this work is the use of metasurface holograms as spatially separable shares, each capable of carrying an encrypted message encapsulated within a holographic image. When combined, these holographic shares reconstruct the original secret image with high fidelity. The single-layer holograms generated by each metasurface serve as identifiers for each shareholder, yet maintain the integrity of the secret as individual layers cannot reveal the encrypted information alone.

The paper demonstrates several key aspects:

1. Cascaded Configuration: When two metasurfaces are stacked at a distance of 100 µm and illuminated by circularly polarized light, the resulting cascade generates a unique holographic image illustrating the encrypted secret—a process not achievable by either metasurface alone.
2. Design and Fabrication: The metasurfaces feature silicon nanofin structures designed using the Pancharatnam-Berry-phase concept, allowing phase manipulation of light with controlled polarization. Different sets of metasurfaces (Set A and Set B) enable multiple configurations by altering spatial overlap, presenting ample opportunities for scalability in application.
3. Imaging Quality: The reconstructed cascaded images achieve nearly equivalent quality to their single-layer counterparts, proving the robustness of the method in terms of optical authentication.
4. Translational Multiplexing: The experiment introduces translational alignment as an additional degree of freedom, allowing for multiplexing of holographic images at different in-plane positions. This illustrates potential for applications such as high-resolution optical rulers.

Implications and Future Directions

This research offers compelling implications for the cryptographic and optical technology fields. Practically, metasurface-mediated secret sharing heralds advancements in secure data handling, intellectual property rights protection, and product authentication—areas heavily reliant on robust encryption. Theoretically, it expands the landscape of metasurface functionality, merging optics and cryptographic sciences innovatively.

The scalability of metasurface arrangements underscores future potential in allowing complex encryption schemes, such as (t, n)-threshold arrangements, where a subset of shares can reconstruct a secret. Furthermore, the design flexibility inherent in metasurfaces suggests future use in dynamic encryption systems when combined with spatial light modulators.

Speculations on AI Integration

Future advancements may witness the integration of AI-driven methodologies into metasurface design frameworks. Predictive algorithms and automated differentiation could enhance metasurface optimization processes, providing greater precision in holographic visualization.

Conclusion

This paper highlights the transformative potential of metasurface holography in encryption technologies. As optical systems converge with cryptographic needs, the innovative use of metasurfaces for secure, scalable secret sharing represents not just an enhancement of existing methodologies, but also a promising avenue towards novel cryptographic applications.