Roadmap on optical security

Postprint (author's final draft

Secure storage and retrieval schemes for multiple encrypted digital holograms with orthogonal phase encoding multiplexing

Recent developments in 3D computational optical imaging such as digital holographic microscopy has ushered in a new era for biological research. Therefore, efficient and secure storage and retrieval of digital holograms is a challenging task for future cloud computing services. In this study, we propose a novel scheme to securely store and retrieve multiple encrypted digital holograms by using phase encoding multiplexing. In the proposed schemes, an encrypted hologram can only be accessed using a binary phase mask, which is the key to retrieve the image. In addition, it is possible to independently store, retrieve, and manage the encrypted digital holograms without affecting other groups of the encrypted holograms multiplexed using different sets of binary phase masks, due to the orthogonality properties of the Hadamard matrices with high autocorrelation and low cross-correlation. The desired encrypted holograms may also be searched for, removed, and added independently of other groups of the encrypted holograms. More and more 3D images or digital holograms can be securely and efficiently stored, retrieved, and managed. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement1

Optical triple random phase encryption

We propose an optical security technique for image encryption using triple random-phase encoding (TRPE). In the encryption process, the original image is first double-random-phase encrypted. The obtained function is then multiplied by a third random-phase key in the output plane, to enhance the security level of the encryption process. This method reduces the vulnerability to certain attacks observed when using the conventional double random-phase encoding (DRPE). To provide the security enhancement of the proposed TRPE method, three attack cases are discussed: chosen-plaintext attacks, known-plaintext attacks, and chosen-ciphertext attacks. Numerical results are presented to demonstrate feasibility and effectiveness of the proposed method. Compared with conventional DRPE, the proposed encryption method can provide an effective alternative and has enhanced security features against the aforementioned attacks

Optical metasurfaces for polarization generation, detection and imaging

Like phase and amplitude, polarization is a fundamental property of light, which can reveal hidden information and has been used in many research fields, including material science, medicine, target detection and biomedical diagnosis. Polarization generation, detection and imaging are of importance for fundamental research and practical applications. Although conventional optics can perform these tasks, it suffers from a complex system, large volume and high cost, which cannot meet the continuing trend of miniaturization and integration. Optical metasurfaces, the two-dimensional counterparts of metamaterials, are planar nanostructured interfaces, which have recently attracted tremendous interest in realizing ultrathin and lightweight planar optical devices. Optical metasurfaces can manipulate light’s amplitude, phase and polarization in a desirable manner, providing a new and compact platform to generate, detect and manipulate light’s polarization. This thesis utilises optical metasurfaces to realise and experimentally demonstrate novel optical devices for polarization generation, detection and imaging. Due to the simplicity of the design and fabrication, this thesis is mainly focused on geometric optical metasurfaces, which are superior to other types of metasurfaces. 2D and 3D polarization structures are generated based on a metalens approach. A ring focal curve, an Archimedean spiral focal curve, and seven-segment-based decimal numbers are experimentally demonstrated in 2D space, while a 3-foil knot, a 4-foil knot, and a 5-foil are realized in 3D space. The geometric metasurfaces are designed based on colour and phase multiplexing and polarization rotation, creating various 3D polarization knots. Various 3D polarization knots in the same observation region can be achieved by controlling the incident wavelengths, providing unprecedented polarization control with colour information in 3D space. Novel polarization detection is experimentally demonstrated through optical holography, light’s orbital angular momentum, and optical ring vortex beams. The measured polarization parameters such as major axis, ellipticity, and handedness are in good agreement with the theoretical prediction. A multifunctional microscope is proposed and developed to image different objects, including biological samples such as cheek cells and beef tendons. For the same sample, five images with different optical properties are obtained on the same imaging plane, which can simultaneously perform edge imaging, polarimetric imaging, and conventional microscope imaging. Benefiting from the ultrathin nature, compactness and multifunctionality of the optical metasurface devices, the integration does not excessively increase the volume of the optical system. With its promising capabilities and potential for expandability, we believe our microscope will herald an exciting new era in biomedical research. The ultrathin nature of optical metasurfaces and their unprecedented capability in light control have provided a compact platform to develop ultrathin optical devices with novel functionalities that are very difficult or impossible to achieve with conventional optics. The metasurface platform for polarization detection and manipulation is very attractive for diverse applications, including polarization sensing and imaging, optical communications, optical tweezers, quantum sciences, display technologies, and biomedical research as well as wearable and portable consumer electronics and optics where miniaturized systems are in high demand

Projektionsalgorithmen im wellenoptischen Transmissionsdesign

Innerhalb dieser Arbeit werden Aspekte des wellenoptischen Transmissionsdesigns untersucht. Die Optimierung von optischen Transmissionsfunktionen entspricht einer Betrachtung des optischen Systems im Funktionsbild. In einem späterem Schritt -- dem Strukturdesign -- kann die ermittelte Transmissionsfunktion in die geometrische Beschreibung eines optischen Elements überführt werden. Zur Optimierung von Transmissionsfunktionen betrachten wir die Anwendung sogenannter Projektionsalgorithmen. Dies sind iterativ arbeitende Algorithmen, bei denen Projektionen auf sogenannte Einschränkungsmengen eingesetzt werden, um für die freien Parameter des Optimierungsproblems eine Lösung zu finden, welche die den Einschränkungsmengen entsprechenden Zielanforderungen möglichst gut erfüllt. Neben einer Untersuchung des Designs diffraktiver Strahlteiler erfolgen in der Arbeit Betrachtungen zur Verbesserung des Konvergenzverhaltens von Projektionsalgorithmen mit Hilfe verstärkter Projektionen. Weiterhin werden sogenannte multifunktionalen Projektionsalgorithmen zur gleichzeitigen Optimierung hinsichtlich einer beliebigen Anzahl von Systemanforderungen entwickelt und deren Einsatz bei der Verbesserung der Toleranzeigenschaften optischer Systeme untersucht