Optical Security Research Articles

Multi-dimensional disturbance secure communication system with dynamic key hiding transmission based on power-domain non-orthogonal multiple access

Data security is becoming more critical in networks as high-speed and large-capacity optical transmission becomes more common. Cryptographic protocols at the MAC layer and higher tiers of the protocol stack are under threat as a result of quantum computer developments. Optical physical layer encryption has great advantages in optical communication security transmission, which can be compatible with a variety of networks, and achieve an efficient and secured ultra-high high-speed data transmission. In this work, we propose a physical layer encryption scheme based on orthogonal frequency division multiplexing power-domain non-orthogonal multiple access (OFDM-PD-NOMA) technique for the dynamic key hiding transmission and multi-dimensional disturbance. The encryption scheme realizes multi-point mutual-coupling key transmission and multi-dimensional disturbance encryption by a 3D discrete chaotic model. The encrypted data and the dynamic key are transmitted together by multichannel signals in PD-NOMA, then, the chaotic signal generated by chaotic generator is used to mask the dynamic key. 3D chaotic sequences generated by the dynamic key are used to encrypt bits, symbols and carriers of the original signal. The initial key, the dynamic key and the chaotic signal realize multi-point mutual-coupling. We conduct a 74.6 Gb/s encrypted quadrature phase shift keying (QPSK)-OFDM-PD-NOMA signal transmission over 2 km 7 core fiber. The key space of encrypted scheme can reach 10462. Finally, experimental results show that the original data can be recovered accurately, and the bit error rate (BER) of the dynamic key is close to zero. The security and reliability of the system have been verified, and this scheme has an important application prospect in the future optical communication system.

Temperature-dependent phase formation of CuInSe2 for self-biased, broadband Si/CuInSe2 heterojunction photodetector

Owing to the numerous applications including optical communication, night vision, remote sensing, and security monitoring, a great interest has emerged in the development of the NIR (near-infrared) photodetectors. In this study, the self-biased Si/CuInSe2 heterojunction photodetectors have been developed and the annealing temperature has been optimized. CuInSe2 thin films have been prepared using the sequential elemental layer deposition followed by annealing at 550, 600, and 650 °C. The CuInSe2 annealed at 550 °C and 650 °C revealed the mixed-phase formation corresponding to CuInSe2 (tetragonal) and Cu7Se4 (Cubic). The CuInSe2 annealed at 600 °C confirmed the transition from mixed-phase to single-phase CuInSe2 tetragonal structure. The impact of annealing temperature-dependent phase formation on the optoelectronic characteristics of Si/CuInSe2 heterojunction has been studied. The Si/CuInSe2 heterojunction formation and photodetection in the self-biased mode have been investigated under varying Halogen light intensity and wavelength-dependent light. The highly sensitive, broadband spectral response and enhanced detectivity in the self-biased mode have been explored in the vicinity of varying annealing temperatures. The optimum Si/CuInSe2 heterojunction photodetector performance was achieved at 600 °C possessing the sensitivity, detectivity, and LDR up to 2.4×103, 0.05×1012 Jones, and 68 dB under Halogen light exposure and 0.8×104, 0.55×1012 Jones and 79 dB under 980 nm light. The present study provides useful insight into the Si/CuInSe2 heterojunction development as an optoelectronic device providing the correlation between the fundamental characteristics of CuInSe2 and its development as a broadband photodetector possessing excellent device performance in the NIR range.

Design and Simulation of Physical Layer Security for Next Generation Intelligent Optical Networks

With the latest technological advancements and attractive features of next generation intelligent optical networks such as high bandwidth, low power consumption, and low transmission loss, etc., they have been considered as most viable solution to satisfy promptly growing bandwidth demands. However, main optical network components bring forth a set of security challenges and reliability issues, accompanied by new vulnerabilities within the network. This paper proposes a new design for an optical encryption and decryption method for enhancing optical network security using p–i–n photodiode which generates Pseudo Random Binary Sequence (PRBS) as a shot noise fluctuations and wavelength converter based design using Semiconductor Optical Amplifier based XOR gate which utilizes Cross-Phase Modulation. The system performance based on Bit Error Rate and Q factor are analyzed at different data rates for different link lengths up to 100 km using OptiSystem. It is observed that error free transmission with a BER of 10–12 is achieved a data rate of 10 Gbps for a link length of only 30 km for the system with PIN photodiode’s shot noise being used for PRBS sequence generation. However, wavelength conversion based system enables transmission of signal at 10Gbps signal up to a link length of 90 km.

Low-dose shift- and rotation-invariant diffraction recognition imaging

A low-dose imaging technique which uses recognition rather than recording of a full high-resolution image is proposed. A structural hypothesis is verified by probing the object with only a few particles (photons, electrons). Each scattered particle is detected in the far field and its position on the detector is analysed by applying Bayesian statistics. Already a few detected particles are sufficient to confirm a structural hypothesis at a probability exceeding 95%. As an example, the method is demonstrated as an application in optical character recognition, where a hand-written number is recognized from a set of different written numbers. In other provided examples, the structural hypothesis of a single macromolecule is recognized from a diffraction pattern acquired at an extremely low radiation dose, less than one X-ray photon or electron per Å2, thus leaving the macromolecule practically without any radiation damage. The proposed principle of low-dose recognition can be utilized in various applications, ranging from optical character recognition and optical security elements to recognizing a certain protein or its conformation.

Random motion blur for optical image encryption

We present a compact optical encryption scheme by using a continuous-random-motion blurring model in an optical imaging system. Image encryption is performed by additive motion blur effects with continuous and random shifts of a camera. Real-time random phase modulation can be achieved without the use of random phase mask. Storage of the key is more convenient, which only requires parameters of motion. In addition, modulation characteristics are different from the traditional encryption schemes. On the premise of high security, modulation space is broadened, and flexibility of encryption is further improved. Simulations and experiments verify the validity of the motion blur-based crypto-system and demonstrate its security under several attacks. This novel method will be significant for the practical applications in the field of optical information security.

Liquid-crystal q-plates with a phase core to generation vortex beams with controllable number of singularities

Based on the method of azo dye photoalignment, electrically controlled liquid crystal (LC) q-plates for the generation of a given number of polarization and phase optical singularities have been designed. The results of experimental studies of polarization and phase characteristics of the generated singular beams are in good agreement with the proposed theoretical model. The proposed devices can be adapted for a variety of problems of modern photonics, including implementation of structured illumination microscopy, information coding, optical security technology, microrheology etc.

Optical encryption based on biometrics and single-pixel imaging with random orthogonal modulation

Computational ghost imaging (CGI), as a novel single-pixel imaging (SPI) technique, has a great potential and bright prospect in the field of optical information security owing to its encryption performances of data compression and real-value ciphertext. However, there are some vulnerabilities in CGI-based encryption technique, such as serious noise in the decrypted result, huge amount of keys, and several potential security loopholes. To address these issues, we propose an optical encryption method based on biometrics and SPI with random orthogonal modulation (ROM) in this paper. The ROM, which is generated by Hadamard matrix, not only improves the clarity of the decrypted images but also reduces the amount of keys to be transmitted. Besides, the security loophole for forgery attack in CGI-based encryption system is effectively blocked by fingerprint key. Both numerical simulations and optical experiments are carried out to test the feasibility and performance of our proposed method.

Optical perfect absorption for information security realized by the novel multi-layered nanofilm structures filled with lossy dopant

Optical absorption devices have been widely used in optical communication, optical information security, optoelectronics and many other optical fields. But, it is very difficult for the device to achieve 100% light absorption. For the above problem, the concept of lossy EMNZ medium has been proposed and the lossy EMNZ medium has been designed by the multi-layered Ag/SiC film structures with lossy dopant based on doping method. Theoretical analysis and simulation experiments show that the proposed structure achieves the ability 100% absorption of light. Compared with coherent perfect absorption (CPA) device, the proposed structure has no requirements for the number and phase of incident light in the process of light absorption, which undoubtedly greatly expands the application range of the structure. The work in this paper has well guiding significance for the development of new high-performance optical absorption devices for information security.

Terahertz switchable VO2-Au hybrid active metasurface holographic encryption.

The combination of metasurface and holographic technology is the most cutting-edge development, but most of the proposed designs are static and do not allow active changes through external stimulation after fabrication, which takes only a limited part of the advantage provided by metasurface. Here, we propose and demonstrate a switchable hybrid active metasurface hologram in the terahertz (THz) regime composed of dynamic pixels (VO2-CSRR) and static pixels (Au-CSRR) based on an intelligent algorithm, which can display some/all information in different temperature ranges. In particular, such performance shows excellent potential in the field of optical communication security, making it a promising candidate. To prove this possibility, we propose a scheme for optical information encryption/decryption and transmission, which takes metasurfaces as carriers of encrypted information and state/polarization/positions as the secret key components. Only when the two matches correctly can we get the hidden real information. The security of our proposed scheme has reached an unprecedented level, providing a new road for communication security.

Synthesis of nano-optical elements for zero-order diffraction 3D imaging

A method is proposed to compute and synthesize a microrelief to produce a new nano-optical element for forming 3D images with full parallax at the zero order of diffraction. The synthesis of nano-optical elements requires the use of multilevel structures. A method is developed for the first time to compute the phase function of such nano-optical elements. Optical security elements that produce the new security feature are synthesized using electron-beam technology. The accuracy of microrelief formation is 10 nm in terms of depth. A sample optical security element is manufactured, which when illuminated by white light, forms a 3D image at the zero order of diffraction. Photos and video of the new 3D visual effect exhibited by real optical elements are presented. The optical elements developed can be replicated using standard equipment employed for manufacturing security holograms. The new optical security feature is easy to control visually, safely protected against counterfeiting, and designed to protect banknotes, documents, ID cards, etc.

Invisible NIR Spectral Imaging and Laser‐Induced Thermal Imaging of Na(Nd/Y)F4@glass with Opposite Effect for Optical Security

AbstractCurrently, advanced optical security techniques are imminent in response to the increasingly rampant counterfeit and pirated goods on a global scale. Herein, hexagonal Na(NdxY1−x)F4 (x = 0–1) solid‐solution nanocrystals (NCs) embedded glasses are successfully fabricated via in situ glass crystallization. Benefited from the protection of inorganic glass, Na(NdxY1−x)F4 NCs exhibit superior long‐term stability and can endure high‐power 808 nm laser irradiation. Importantly, opposite variations between near‐infrared (NIR) luminescence and laser‐induced temperature can be detected for the nanocomposites, which are sensitive to Nd3+ doping concentration. As a proof‐of‐concept experiment, Nd3+ concentration dependent anti‐counterfeiting patterns with high‐concealment and high‐precision are designed and show bright emission and dimmish thermal images in Nd3+‐tenuous composites under the irradiation of 808 nm laser, while opposite displays can be achieved in Nd3+‐enriched one. This kind of information encryption triggered by a commercial single light source to achieve dual opposing displays in one material can effectively improve security in anti‐counterfeiting.

Asymmetric Dichroic Colors in Stretchable Film with Embedded Au/Ag Alloy Nanoparticles.

We present a new type of stretchable dichroic film in which Au and Ag alloy nanoparticles (NPs) are dispersed in polydimethylsiloxane (PDMS). The alloy NPs are synthesized with different atomic compositions and sizes to modulate their plasmonic resonance frequencies and absorption and scattering cross sections. The PDMS dichroic film in which 100 nm alloy NPs with a Au/Ag ratio of 7:3 are dispersed shows exotic optical properties under tensile strain. When 40% tensile strain is applied, the film exhibits a strain-sensitive transmission and strain-insensitive reflection behavior in which the transmittance is increased up to 2.6 times, whereas the reflectance remains unchanged. Moreover, we demonstrate a stretchable anticounterfeiting film and a flexible dichroic sculpture fabricated with the PDMS composite. This work demonstrates a new type of plasmonic application that has great potential in various applications, such as special-purpose optical films, security patterns, and smart windows.

Optical communication security transmission based on blockchain

Optical communication security transmission based on blockchain

Exploiting Reservoir Computing for Optical Secure Communication

Abstract A reservoir computing (RC) based on vertical cavity surface emitting laser (VCSEL) subjected to optical feedback is adopted to realize chaos synchronization in optical chaotic communication. Combined with the application of chaos masking (CMS) technology in chaotic secure communication, chaotic signal generated by distribution feedback (DFB) laser after optical feedback and optical injection, that is used as chaotic carrier of hiding original information, and act as target signal of the RC. Then masked information is used for RC training and transmission. Next, utilizing the weights and error offsets trained out by RC at transmitter, carrier can be reconstructed by RC at receiver. Finally, message is acquired by subtracting the reconstructed carrier from received masked signal. Taking image data transmission in 10 km fiber as an example, the chaos synchronization between the carrier signal and the constructed carrier signal is 0.9935, Q-factor is 10 and bit error rate (BER) is 5×10-28 with simulation.

Erasable glass-stabilized perovskite quantum dots for NIR-laser-stimuli-responsive optical security

Stimuli-responsive smart luminescent materials capable of dynamic color emission with distinct spectral profile/intensity are highly desirable for anti-counterfeiting applications. Here, we report the dynamic manipulation of photoluminescence from metal halide CsPbX 3 (X = Br, I) perovskite quantum dots (PeQDs) inside a glass medium by tuning local temperature fields in real time in combination with the efficient photothermal material CsYb 2 F 7 @glass. Benefiting from the effective protection of the inorganic glass matrix and low exciton binding energy of PeQDs, it is feasible to realize stable and reversible ON/OFF full-spectral emissions of PeQDs upon commercial 980 nm laser stimulation. The dynamic combination of downshifting PeQDs and upconverting lanthanide-doped CsYb 2 F 7 can be elaborately designed to produce a series of erasable photochromic anti-counterfeiting patterns and multi-dimensional optical encodings. • An approach to dynamically manipulate PL of CsPbX 3 QDs inside glass is developed • Laser-induced Ln 3+ photothermal effect is used to lighten/quench PL of CsPbX 3 @glass • Erasable photochromic anti-counterfeiting and optical encodings are demonstrated Wang et al. demonstrate the dynamic manipulation of erasable emissions from CsPbX 3 perovskite quantum dots (PeQDs) inside a glass medium by tuning local temperature fields in real time with the help of the efficient photothermal material CsYb 2 F 7 . This controllable combination of rare-earth/PeQDs may enable their practical application in high-level optical security.

Simultaneous achievement of sensitivity enhancement and dual-mode luminescence through co-doping Eu3+ in Ca2MgWO6:Er3+/Yb3+ phosphor

Demands for temperature probe technologies and information security have driven the development of luminescent materials doped with lanthanide ions (Ln3+) because of their distinctive optical properties. Nevertheless, the problems of poor temperature sensing performance and single-mode luminescence restrict most materials' applications in the fields of temperature sensing and optical anti-counterfeiting. Herein, we have effectively achieved the enhancement of the temperature sensing sensitivity factor and the multi-mode anti-counterfeiting at the same time by co-doping Eu3+ in the up-conversion Ca2MgWO6:Er3+/Yb3+ material. The maximum absolute sensitivity based on the 2H11/2/4S3/2 couples of Er3+ increased from 81.83 × 10−4 K−1 at 423 K to 88.12 × 10−4 K−1 at 398 K, which was attributed to the energy transfer between Er3+ and Eu3+ which increases the fluorescence intensity ratio values. Utilizing the down-conversion luminescence characteristics of Eu3+ ion, phosphors exhibited color tunability under 980 nm and 365 nm excitations to achieve dual-mode anti-counterfeiting function. Meanwhile, the fluorescent anti-counterfeiting pattern prepared by screen printing technology helped materials towards emerging anti-counterfeiting applications. Therefore, the novel phosphors have potential applications in noncontact temperature sensing and optical anti-counterfeiting security fields.

Unclonable Anti‐Counterfeiting Labels Based on Plasmonic‐Patterned Nanostructures

Herein this study, plasmonic‐patterned nanostructures are applied to fabricate unclonable anti‐counterfeiting labels. Patterned Au nanoparticles (AuNPs) are constructed by the skillful combination of diblock copolymer polystyrene‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) self‐assembly with shadow mask lithography to provide a simple and universal approach for large‐area fabrication of patterned nanostructures. The AuNP pattern can be made visible by increasing the nanoparticle size. A surface‐enhanced Raman spectroscopy (SERS)‐based physical unclonable function (PUF) security label with a large encoding capacity is fabricated by depositing malachite green (MG) on the surface. The broadening of the size distribution of the AuNPs after their growth and the increased disorder in their arrangement confer the security label with unique and unclonable characteristics. The as‐prepared optical PUF security label is read out by a confocal Raman spectrometer to extract binary codes, which are then authenticated through comparison. These SERS‐based PUF security labels, which combine patterning with stochastic spectral encoding, not only provide rich and diverse patterns but are also promising for anti‐counterfeiting applications in areas such as rigid silicon‐based optoelectronic materials and devices.

Multicolor Light Mixing in Optofluidic Concave Interfaces for Anticounterfeiting with Deep Learning Authentication.

Anticounterfeiting technology has received tremendous interest for its significance in daily necessities, medical industry, and high-end products. Confidential tags based on photoluminescence are one of the most widely used approaches for their vivid visualization and high throughput. However, the complexity of confidential tags is generally limited to the accessibility of inks and their spatial location; generating an infinite combination of emission colors is therefore a challenging task. Here, we demonstrate a concept to create complex color light mixing in a confined space formed by microscale optofluidic concave interfaces. Infinite color combination and capacity were generated through chaotic behavior of light mixing and interaction in an ininkjet-printed skydome structure. Through the chaotic mixing of emission intensity, wavelength, and light propagation trajectories, the visionary patterns serve as a highly unclonable label. Finally, a deep learning-based machine vision system was built for the authentication process. The developed anticounterfeiting system may provide inspiration for utilizing space color mixing in optical security and communication applications.

Single Exposure Phase-Only Optical Image Encryption and Hiding Method via Deep Learning

Phase-only optical image security technology Based on one-time pad is an encryption and hiding method by introducing random key through phase modulation, which can improve the security of the system to a great extent. The application of traditional phase-only optical image encryption and hiding (POIEH) method is often limited by the amount of data and the quality of decrypted image. In this paper, a single exposure POIEH method using deep learning (DL) is proposed. The original image and corresponding encrypted hidden interferogram acquired with POIEH system are constructed to the train datasets for the learning of an end-to-end designed U-net, then the corresponding relationship between the encrypted hidden interferogram and the reconstructed image is learned and only single-frame encrypted hidden interferogram is needed to perform the reconstruction of POIEH. This method can realize real-time image encryption and hiding and high-quality decryption with only one interferogram. Simulation results and performance analysis show that the proposed method has higher security, stronger generalization ability and robustness.

Capacity expansion of chaotic secure transmission system based on coherent optical detection and space division multiplexing over multi-core fiber.

We propose and experimentally study a coherent optical chaotic secure transmission system through a multi-core fiber (MCF). The messages are encrypted by the chaotic carrier and transmitted through the outer cores of the MCF, whereas the chaotic carrier signal is concealed by transmitting through the center core. The MCF provides large transmission capacity expansion and security enhancement against eavesdroppers due to its physical structure. In addition, the designed optical chaos self-homodyne coherent detection strategy has high detection sensitivity and simple physical structure. Due to the prevalence of devices and digital signal processing (DSP) algorithms used in this system, it can be well compatible with a commercial coherent optical communication system. Error free 40 Gb/s/core encrypted 16 quadrature amplitude modulation (QAM) signal transmission over 10 km 7-core fiber is achieved, and 20 Gb/s quadrature phase shift keying (QPSK) signal transmission over a 100 km standard single-mode fiber (SSMF) is demonstrated to verify the long-distance transmission capability. The sensitivity to the secret key is also studied.