Metasurface‐Based Optical Fractional Fourier Transform: Implementation and Applications

ABSTRACT The fractional Fourier transform (FrFT), a generalization of the classical Fourier transform (FT) with a fractional‐order parameter, enables flexible tuning between time and frequency domains, making it a powerful tool in signal processing. However, its utility in optics is constrained by the lack of compact, efficient analog implementation platforms, limiting progress in optical information processing. Herein, a compact analog optical FrFT system based on metasurface phase planes able to realize accurate analog FrFT computation is presented. Building on this platform, and leveraging FrFT's unique advantages of tunable fractional orders and independent time‐frequency domains, two novel image encryption algorithms are developed: a single‐image scheme integrated with Arnold transform for enhanced scrambling, and a dual‐image scheme enabled by iterative computation for parallel data processing. Comprehensive numerical calculations, optical simulations, and physical experiments validate the robustness and reliability of the proposed system and algorithms. Notably, the tunable fractional order of FrFT provides a large encryption key space and high key sensitivity, significantly boosting encryption security. This work establishes a versatile analog optical FrFT platform and two high‐security encryption schemes, offering a new paradigm for advancing optical information processing, paving the way toward developing practical optical cryptosystems.