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Quantum key distribution (QKD), ensuring the unconditional security of information, attracts a significant deal of interest. An important task is to design QKD systems as a platform for education as well as for research and development applications and fast prototyping new QKD protocols. Here, we present a modular QKD setup driven by National Instruments (NI) cards with open source LabView code, open source Python code for post-processing procedures, and open source protocol for external applications. An important feature of the apparatus developed is its flexibility offering the possibility to modify optical schemes, as well as prototype, and verify novel QKD protocols. The other distinctive feature of the setup developed is the implementation of the decoy-state protocol, which is a standard tool for secure long-distance quantum communications. By testing the plug-and-play scheme realizing BB84 and decoy-state BB84 QKD protocols, we show that the developed QKD setup shows a high degree of robustness beyond laboratory conditions. We demonstrate the results of the use of the developed modular setup for QKD experiments in the urban environment. [ABSTRACT FROM AUTHOR]

Highilights • Optical image authentication scheme using dual polarization decoding is purposed and validated. • We examine a sparse encoding method based on image division to process the original image. • The proposed scheme resolves the alignment problem of previous polarization encoding methods. • Our verification system exhibits high robustness and flexibility against attacks and interference. • Results might be useful for polarization-encoding based optical verification. Abstract We report on an optical image authentication scheme using dual polarization decoding configuration. We examine a sparse encoding method based on image division to process the original image. Next, the sparse original image is separated into two noise-like structure images with random polarization parameters which are digitally encoded. During the decoding stage, the encoded images are sent into a dual polarization decoding configuration where a pixelated polarizer with sparse distribution of transmission angle is employed for image recovering. The proposed scheme avoids complicated recording of complex information and resolves the alignment problem of previous polarization encoding methods. Then we examine numerical simulations to show that the proposed scheme is well suited to recover the original image when decryption keys are correctly used. We find evidence that the verification system exhibits high robustness and flexibility against attacks and interference. We expect that these results might be useful for polarization-encoding based optical verification. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) provides theoretic information security in communication based on the laws of quantum physics. In this work, we report an implementation of quantum-secured data transmission in the infrastructure of Sberbank of Russia in standard communication lines in Moscow. The experiment is realized on the basis of already deployed urban fiber-optics communication channels with significant losses. We realize the decoy-state BB84 QKD protocol using the one-way scheme with polarization encoding for generating keys. Quantum-generated keys are then used for continuous key renewal in the hardware devices for establishing a quantum-secured VPN Tunnel between two offices of Sberbank. The hybrid approach used offers possibilities for long-term protection of the transmitted data; it is promising for integrating in the already existing information security infrastructure. [ABSTRACT FROM AUTHOR]

In recent years, dielectric and metallic nanoscale metasurfaces are attracting growing attention and are being used for variety of applications. Resulting from the ability to introduce abrupt changes in optical properties at nanoscale dimensions, metasurfaces enable unprecedented control over light's different degrees of freedom, in an essentially two-dimensional configuration. Yet, the dynamic control over metasurface properties still remains one of the ultimate goals of this field. Here, we demonstrate the optical resonant interaction between a form birefringent dielectric metasurface made of silicon and alkali atomic vapor to control and effectively tune the optical transmission pattern initially generated by the nanoscale dielectric metasurface. By doing so, we present a controllable metasurface system, the output of which may be altered by applying magnetic fields, changing input polarization, or shifting the optical frequency. Furthermore, we also demonstrate the nonlinear behavior of our system taking advantage of the saturation effect of atomic transition. The demonstrated approach paves the way for using metasurfaces in applications where dynamic tunability of the metasurface is in need, for example, for scanning systems, tunable focusing, real time displays, and more. [ABSTRACT FROM AUTHOR]

• A coding strategy based on polarization and light intensity is adopted. • The method can be easily combined into different types of phase-shifting methods. • Defocused binary fringe projection method encodes the degree of polarization. Polarized structured light is an important method to measure shiny surface. In this paper, a type of structured light encoded by polarized light is proposed. A coding strategy based on polarization and light intensity is adopted to improve the quality of the projection fringe. A type of robust phase-shift fringe is generated using the characteristics of a liquid crystal display projector by the defocus method. Compared with other polarized structured light coding methods, the proposed method requires simpler equipment and no additional custom instruments. Experiments show that the method could effectively improve the robustness of fringes. Experiments suggest that the range accuracy is improved by 2.4%. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate experimentally an intrinsically stable polarization coding and decoding system composed of optical-fiber Sagnac interferometers with integrated phase modulators for quantum key distribution. An interference visibility of 98.35% can be kept longtime during the experiment without any efforts of active compensation for coding all four desired polarization states. [Copyright &y& Elsevier]

Abstract: We present an optical encryption method based on geometrical phase, which is originated from polarization manipulation. The decrypted picture is retrieved by measuring the polarization of the beam emerging from the encrypted element. The encrypted element is achieved by using a computer-generated space-variant subwavelength dielectric grating. Theoretical analyses of the optical concept by use of Jones and Mueller formalisms, as well as experimental results including full optical decryption process are introduced. Digital implementation and the possibility of using watermarking are also discussed. [Copyright &y& Elsevier]

• A compact optical authentication system using generator of spatially variant vector beam is proposed. • A novel sparse sampling technique of ciphertexts is developed that can simultaneously complete information removal and data compression. • Requirement for strict alignment of phase mask key is relaxed greatly. • Random polarization parameters constitute a key space with multiple dimension to resist against potential brute force attacks. An innovative image authentication scheme using spatially variant vector beam is introduced. During encoding period, the original image is converted into two angle distribution images by making use of the modified Gerchberg–Saxton algorithm (MGSA) and random polarization parameters in a digital way. By using image division and sparse sampling, two mosaic ciphertexts which retain partial encoded information are obtained. A generator of spatially variant polarized beam, combined with a sparse phase-only key, can decrypt the ciphertexts into a noise-like result that can be authenticated by a nonlinear correlator. Numerical simulation tests demonstrate the security strength and robustness of this scheme. Moreover, this scheme exhibits a higher resistance against misalignment of phase-only key, which is advantageous for practical implementation. We expect that these results might be useful for future application of polarization encoding in security application. [ABSTRACT FROM AUTHOR]