Abstract
AbstractSecuring optical information to avoid counterfeiting and manipulation by unauthorized persons and agencies requires innovation and enhancement of security beyond basic intensity encryption. In this paper, we present a new method for polarization-dependent optical encryption that relies on extremely high-resolution near-field phase encoding at metasurfaces, down to the diffraction limit. Unlike previous intensity or color printing methods, which are detectable by the human eye, analog phase decoding requires specific decryption setup to achieve a higher security level. In this work, quadriwave lateral shearing interferometry is used as a phase decryption method, decrypting binary quick response (QR) phase codes and thus forming phase-contrast images, with phase values as low as 15°. Combining near-field phase imaging and far-field holographic imaging under orthogonal polarization illumination, we enhanced the security level for potential applications in the area of biometric recognition, secure ID cards, secure optical data storage, steganography, and communications.
Highlights
Information security is an important concern in daily life from civil to military applications [1, 2]
Other attempts have been made for metasurface encryption, such as the combination of color printing and the holographic image [39, 40], image postprocessing based on spatial frequency [41], and tunable meta-hologram [42]
As a proof of concept, we demonstrate a binary quick response (QR) code in the single-channel metasurface (SC-MS) with the binary encoded phase of φh and φl for phase imaging
Summary
Information security is an important concern in daily life from civil to military applications [1, 2]. Optical encryption for information security has gained enormous attention owing to its ability to provide many degrees of freedom to encode the information relying on various optical channels such as frequency, amplitude, phase, and polarization [3, 4]. These efforts led to various encryption methods, including Lippmann plate [5], spatial correlators [6], and holograms [7]. Metasurfaces have been designed to perform far-field holographic encoding using the concept of meta-holograms. All of the proposed metasurface encryptions, relying either on the intensity of the color
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