Optical Security Research Articles

High-temperature dynamic luminescence of MgGa2O4: Tb3+, Er3+ phosphors for advanced anti-counterfeiting and information encryption

Long persistent luminescence (LPL) anti-counterfeiting technology is widely used in optical information storage, information security, and anti-counterfeiting fields due to the advantages of non-interference with background light and high imaging resolution. However, the performance of most LPL materials is greatly compromised in harsh environments such as high temperature, which seriously affects the effectiveness of anti-counterfeiting measures due to the accelerated decay rate of LPL luminescence. In this work, we synthesized a series of MgGa2O4: Tb3+ (MGO: Tb3+), which possess stable crystal structure with obvious LPL properties above room temperature, and the optimum temperature is determined to be 423 K. Moreover, the additional introduction of Er3+ ions enhances the security of anti-counterfeiting, and the combination of photo-stimulated luminescence (PSL) and upconversion (UC) phenomena enables color tuning from red to orange to green by extending the 980 nm laser irradiation time. Finally, the anti-counterfeiting strategy utilizing MGO: Tb3+ and MGO: Tb3+, Er3+ possesses an extremely high level of security, making it an attractive performance for designing advanced anti-counterfeiting technology.

Optical voice security scheme for anticounterfeiting

In this work, we propose an optical voice security scheme for anticounterfeiting that uses voice watermark recording by an optical setup of parallel phase shifting digital holography (PPSDH) and an approach of converting the recorded voice into a suitable 2D voice watermark. The converted voice watermark is further encrypted in the optical domain in order to provide enhanced security in terms of physical keys for watermarking and other applications. The proposed scheme makes it difficult for counterfeiting in order to claim the ownership of voice or image data in case of watermarking. We present the experimental results of voice watermark recorded by optical microphone based on PPSDH and simulation results to verify the proposed optical security scheme for watermarking of optically recorded data. Best of our knowledge, this is the first proposal towards voice watermark generation in optical domain and the first demonstration of it for watermarking.

Er3+/Tm3+ co-activated core@shell nanoarchitectures: tunable upconversion luminescence and high-security anti-counterfeiting

Currently, developing advanced optoelectronic materials is of great importance to solving serious problem of fake and shoddy products. Lanthanide-doped nanomaterials are particularly suitable for addressing this issue, but limited by the realization of multiple upconverison (UC) emissions upon a single-wavelength laser excitation. Herein, it is proven that the co-dopant of blue/near-infrared (NIR)-emitting activators (Tm3+) and green/red-emitting centers (Er3+) in a particular designed core–shell nanoarchitecture allows the achievement of multiple luminescence over wide spectral region for optical security. In our study, cubic-phased NaYbF4:Tm/Er@CaF2 nanocrystals have been successfully synthesized through a layer-by-layer coprecipitation strategy, which presents visible multicolor UC luminescence and invisible NIR UC emission upon 980 nm laser excitation by just regulating the laser power and temperature. Significantly, the unique luminescent characteristics enables the designed UC nanoparticles a promising candidate for advanced anti-counterfeiting. This works offers a reference to develop advanced optoelectronic materials for practical application in optical security.

Effect of Input Layer Signal Polarization on the Dynamics of Optical Neural Networks

The polarization encoding-based optical validation and security verification approach is provided in this paper. This technique involves simulating information optically and bonding it to a polarization-encoded mask, such as a biological order or a reaction. The linear polarizers that make up the polarization-encoded mask are positioned at random. The polarization-encoded signal is the name given to this composite signal. In this simulation study, a primary optical neural network adapting a light brain technology is proposed theoretically based on a feed-forward model. Calibration of the nonlinear behavior in such a network is assumed by a semiconductor laser of the Distributed Feedback (DFB) type. Four laser networks are constructed as three influencers, followed by one embedding laser followers. Each of the influencer’s lasers has a different wavelength frequency and polarization (30-60–90) degree, respectively, and then combines the signal with WDM for the last laser. With each value, from the last values, of the polarization effect after this effect, the results indicated that these values would present the greatest weight of spikes and chaotic behavior for the uploaded virtual message.

Optical authentication method based on correspondence ghost imaging.

Ghost imaging technology has a great application potential in optical security because of its non-local characteristics. In this paper, on the basis of computational ghost imaging, an optical authentication scheme is proposed that utilizes the correspondence imaging technique for the preliminary reconstruction of the object image, and then authenticates the image by a nonlinear correlation algorithm. Different from the previous optical authentication schemes that usually adopted random selection of measurements, this authentication method consciously selects the bucket detector measurement values with large fluctuation and can achieve authentication using ultra-low data volumes less than 1% of the Nyquist limit. In brief, this scheme is easy to implement and has a simpler algorithm and higher stability, which is a tremendous advantage in practical optical authentication systems. The simulation and physical experimental results demonstrate the feasibility of the scheme.

100Gb/s coherent optical secure communication over 1000 km based on analog-digital hybrid chaos.

In recent years, the transmission capacity of chaotic secure communications has been greatly expanded by combining coherent detection and multi-dimensional multiplexing. However, demonstrations over 1000 km fiber are yet to be further explored. In this paper, we propose a coherent optical secure transmission system based on analog-digital hybrid chaos. By introducing an analog-digital converter (ADC) and a bit extraction into the feedback loop of entropy source, the broadband analog chaos is converted into a binary digital signal. This binary digital signal is then mapped to a 65536-level pulse amplitude modulation (PAM) signal and injected into the semiconductor laser (SL) to regenerate the analog chaos, forming a closed loop. The binary digital signal from the chaos source and the encrypted signal are transmitted via wavelength division multiplexing (WDM). By using conventional digital signal processing (DSP) algorithms and neural networks for post-compensation, long-haul high-quality chaotic synchronization and high-performance secure communication are achieved. In addition, the probability density distribution of the analog chaotic signal is effectively improved by adopting the additional higher-order mapping operation in the digital part of the chaos source. The proof-of-concept experimental results show that our proposed scheme can support the secure transmission of 100 Gb/s quadrature phase shift keying (QPSK) signals over 1000 km of standard single-mode fiber (SSMF). The decrypted bit error rate (BER) reaches 9.88 × 10-4, which is well below the 7% forward error correction (FEC) threshold (BER = 3.8 × 10-3). This research provides a potential solution for high-capacity long-haul chaotic optical communications and fills the gap in secure communications based on analog-digital hybrid chaos.

Transfer-Printing Hydrogel-Based Platform for Moisture-Driven Dynamic Display and Optical Anti-Counterfeiting.

Humidity-responsive materials offer a promising approach to achieving tunable metasurface systems due to their fast and reversible swelling responses to moisture, which enables many important applications, such as real-time humidity sensing, optical switches, dynamic displays, and optical information encryption. However, the humidity-responsive structural coloration generally cannot provide a high spatial resolution and requires a complex patterning process. Here, we present a scalable moisture-driven color-changing Fabry-Pérot (FP)-like cavity composed of a polyvinyl alcohol layer sandwiched between an upper gold nanoparticles assembly and a bottom gold mirror. Through nanoparticle contact printing, we pixelated these cavities with sub-micrometer sizes without crosstalk and achieved an ultrahigh display resolution of ∼400 nm. Meanwhile, these nanoparticle-based FP (NBFP) cavities exhibit more vibrant colors than those of conventional film-based ones due to broadband absorption of the disordered nanoparticle assembly. Moreover, the NBFP cavities exhibit a rapid response (<300 ms), benefiting from the membrane pores formed in the gaps between the adjacent nanoparticles. Finally, we demonstrated the applications of the NBFP cavities in optical anti-counterfeiting and dynamic multi-color printing. These results suggest that our approach will help to realize a colorful, fast, and ultrahigh-resolution dynamic display device in optical security and colorimetric sensing.

Vectorial‐Manipulating Encryption for Multi‐Channel Capacity and Security Enhancement

AbstractEmerging meta‐optics unfold unprecedented capabilities in optical display, information storage, and encryption applications. Particularly, the recent advances in vectorial holography based on the multi‐parameter manipulation of the Jones matrix have increased the modulation space and information capacity. However, the fundamental degree of freedom (DoF) extreme limit in the optical encoding space of the Jones matrix bottlenecks the information capacity for high‐demand practical applications. To further expand the high‐volume encryption with enhanced security, here, a vectorial‐manipulating encryption strategy is proposed to originally demonstrate multi‐channel encryption and display. By ingeniously utilizing multi‐beam overlapping and precisely controlling their phase differences in the overlapping area, the capacity expansion of up to 12‐channel near‐/far‐field optical images is enabled. Such vectorial‐manipulating strategy is also applied to near‐field nanoprinting and realizes additional encrypted nanoprinting information. More intriguingly, the optical encryption will not be decrypted unless setting with a particular combination of input/output polarization keys, thus enhancing its concealment security beyond the conventional encryption. Overall, the proposed vectorial‐manipulating strategy expands the state‐of‐the‐art storage capacity with enhanced decipher security and potentially suggests a new path for the next‐generation optical storage and encryption security applications.

RETRACTED ARTICLE: Radio optical network security analysis with routing in quantum computing for 5G wireless communication using blockchain machine learning model

RETRACTED ARTICLE: Radio optical network security analysis with routing in quantum computing for 5G wireless communication using blockchain machine learning model

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes.

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Spatially Resolved Organic Whispering‐Gallery‐Mode Hetero‐Microrings for High‐Security Photonic Barcodes

AbstractWhispering‐gallery‐mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero‐microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge‐transfer (CT) strength, full‐color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high‐quality photonic barcodes. Notably, the spatially resolved WGM hetero‐microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero‐emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Multicolored Displays with Selective Visible‐Infrared Spectral Modulation for Optical Information Transmission

AbstractPolyaniline (PANI) can achieve reversible optical modulation in visible and infrared (IR) bands under the action of voltage. However, PANI‐based electrochromic devices cannot cope with the dual detection of visible and IR light to realize the transmission of information due to the linkage restriction between the spectral modulation in the visible and IR region. Here, IR low‐absorptive inorganic pigments as colorants and IR high‐transparent polymer as a binder are utilized to prepare colored films with high transparency. A camouflage layer against visible light detection is constructed on the surface of IR electrochromic devices, and the information transmission is realized in the IR band by controlling the thermal radiation characteristics. Furthermore, thermochromic microcapsules (TMs) that change color under external thermal stimuli are introduced to fabricate a thermochromic and IR transparent functional layer, which is attached to the surface of IR electrochromic devices and endows the devices with separate spectral modulation ability in the visible and IR region. Multicolored displays are fabricated by arraying various devices. Moreover, visual patterns are prepared on the surface of IR electrochromic devices by dispensing technology. This configuration endows the device with a promising potential for anti‐counterfeiting, optical security, and related applications.

Utilization of Physical Anisotropy in Metal-Organic Frameworks via Post-Synthetic Alignment Control with Liquid Crystal.

Metal-organic frameworks (MOFs) represent crystalline materials constructed from combinations of metal and organic units to often yield anisotropic porous structures and physical properties. Postsynthetic methods to align the MOF crystals in bulk remain scarce yet tremendously important to fully utilize their structure-driven intrinsic properties. Herein, we present an unprecedented composite of liquid crystals (LCs) and MOFs and demonstrate the use of nematic LCs to dynamically control the orientation of MOF crystals with exceptional order parameters (as high as 0.965). Unique patterns formed through a facile multidirectional alignment of MOF crystals exhibit polarized fluorescence with the fluorescence intensity of a pattern dependent on the angle of a polarizer, offering potential use in various optical applications such as an optical security label. Further, the alignment mechanism indicates that the method is applicable to numerous combinations of MOFs and LCs, which include UV polymerizable LC monomers used to fabricate free-standing composite films.

Encryptable Electrochromic Smart Windows: Uniaxially Oriented and Polymerized Hierarchical Nanostructures Constructed by Self-Assembly of Tetrathiafulvalene-Based Reactive Mesogens.

Tetrathiafulvalene (TTF)-based reactive mesogens (TTF-E and TTF-T) are synthesized, self-assembled, uniaxially oriented, and polymerized for the development of encryptable electrochromic smart windows. Electrochemical and spectroscopic experiments prove that the self-assembled TTF mixture (TTFM, TTF-E:TTF-T = 1:1) can reversibly switch the absorption wavelength of the TTF chromophore according to the redox reactions. Based on the identification of the phase transition and crystallographic structure, uniaxially oriented hierarchical nanostructures are easily constructed on the macroscopic area by simple coating and a self-assembly process. Subsequent polymerization of hierarchical nanostructures of TTFM significantly enhances thermal and mechanical stabilities and makes it possible for them to be fabricated as an electrochromic device. The angularly dependent correlation between the anisotropy of mesogens and the linearly polarized light allow us to demonstrate TTFM as smart windows capable of various optical security applications, including privacy protection and information encryption.

Construction of a Reversible Solid-state Fluorescence Switching Via Photochromic Diarylethene and Si-ZnO Quantum Dots.

Developing fluorescence switching as functional system is highly desirable for potential applications in the fields of light-responsive materials or devices. Attempt to construct fluorescence switching system tend to focus on the high fluorescence modulation efficiency, especially in solid state. Herein, a photo-controlled fluorescence switching system was constructed with photochromic diarylethene and trimethoxysilane modified zinc oxide quantum dots (Si-ZnO QDs) successfully. It was verified by the measurement of modulation efficiency, fatigue resistance as well as theoretical calculation. Upon irradiation with UV/Vis lights, the system exhibited excellent photochromic property and photo-controlled fluorescence switching performance. Furthermore, the excellent fluorescence switching characters could also be realized in solid state and the fluorescence modulation efficiency was determined to be 87.4%. The results will provide new strategies to the construction of reversible solid-state photo-controlled fluorescence switching for the application in the fields of optical data storage and security labels.

Multispectral Imaging with a Planar Cavity-Type Metasurface for Optical Security.

Multispectral imaging refers to capturing images in different wavelength ranges across the electromagnetic spectrum. Despite the potential impact of multispectral imaging, its widespread use has been limited by the poor spectral selectivity of naturally occurring materials beyond the visible range. In this study, we present a multilayered planar cavity structure to simultaneously record mutually independent visible and infrared (IR) images on solid surfaces. The structure consists of a color control unit (CCU) and an emission control unit (ECU). The visible color of the cavity is controlled by varying the thickness of the CCU, whereas its IR emission is spatially tuned by the laser-induced phase change of a Ge2Sb2Te5 layer embedded in the ECU. Because the CCU comprises only IR lossless layers, its thickness variation has negligible influence on the emission profile. This enables different color and thermal images to be printed in a single structure. The cavity structure can be fabricated on flexible substrates (plastic and paper) as well as rigid bodies. Furthermore, the printed images remain stable against bending. This study shows that the proposed multispectral metasurface is highly promising for use in the field of optical security, such as identification, authentication, and anti-counterfeiting.

Optical multiple-image authentication based on computational ghost imaging and hybrid non-convex second-order total variation.

An optical security method for multiple-image authentication is proposed based on computational ghost imaging and hybrid non-convex second-order total variation. Firstly, each original image to be authenticated is encoded to the sparse information using computational ghost imaging, where illumination patterns are generated based on Hadamard matrix. In the same time, the cover image is divided into four sub-images with wavelet transform. Secondly, one of sub-images with low-frequency coefficients is decomposed using singular value decomposition (SVD), and all sparse data are embedded into the diagonal matrix with the help of binary masks. To enhance the security, the generalized Arnold transform is used to scramble the modified diagonal matrix. After using SVD again, the marked cover image carrying the information of multiple original images is obtained using the inverse wavelet transform. In the authentication process, the quality of each reconstructed image can be greatly improved based on hybrid non-convex second-order total variation. Even at a very low sampling ratio (i.e., 6%), the existence of original images can be efficiently verified using the nonlinear correlation maps. To our knowledge, it is first to embed sparse data into the high-frequency sub-image using two cascaded SVDs, which can guarantee high robustness against the Gaussian filter and sharpen filter. The optical experiments demonstrate the feasibility of the proposed mechanism, which can provide an effective alternative for the multiple-image authentication.

Filterless and High-Speed InP Near-Infrared Photodetector With an Ultra-Small Full-Width at Half Maximum

Near-infrared narrowband photodetection between 920 and 960 nm is quite appealing for many applications, such as optical communication, security monitoring, and machine vision, owing to the weak photon-scattering effect and the low intensity of sunlight in this range. Herein, a self-powered narrowband InP photodetector is realized based on a junction-controlled charge-collection narrowing (JCCN) mechanism, exhibiting a peak response centered at 954 nm with a full width at half maximum (FWHM) of 17 nm. Thanks to the reflection of the Schottky electrode and the passivation of the Al2O3 layer, the peak specific detectivity of the device can be up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.5\times 10^{{11}}$ </tex-math></inline-formula> Jones and a linear dynamic range (LDR) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 99 dB is achieved under the illumination of 954 nm. Moreover, the device shows long-term stability and excellent repeatability with a −3 dB frequency of 87.3 kHz. Furthermore, unless the wavelength of the background light is in the range of 945–967 nm, the crosstalk value of the device remains below −10 dB. These results signify that the present InP photodetector is a promising building block for future near-infrared optoelectronic systems.

Hashing for secure optical information compression in a heterogeneous convolutional neural network

In recent years, heterogeneous machine learning accelerators have become of significant interest to science, engineering, and industry. At the same time, the looming post-quantum encryption era instigates the demand for increased data security. From a hardware processing point of view, electronic computing hardware is challenged by electronic capacitive interconnect delay and associated energy consumption. In heterogeneous systems, such as electronic–photonic accelerators, parasitic domain crossings limit throughput and speed. With analog optical accelerators exhibiting a strong potential for high throughput (up to petaoperations per second) and operation efficiency, their ability to perform machine learning classification tasks on encrypted data has not been broadly recognized. This work is a significant step in that direction. Here, we present an optical hashing and compression scheme that is inspired by SWIFFT, a post-quantum hashing family of algorithms. High degree optical hardware-to-algorithm homomorphism allows one to optimally harvest the potential of free-space data processing: innate parallelism, low latency tensor by-element multiplication, and zero-energy Fourier transformation operations. The algorithm can provide several orders of magnitude increase in processing speed as compared to optical machine learning accelerators with non-compressed input. This is achieved by replacing slow, high-resolution CMOS cameras with ultra-fast and signal-triggered CMOS detector arrays. Additionally, information acquired in this way will require much lower transmission throughput, less in silico processing power, storage, and will be pre-hashed, facilitating optical information security. This concept has the potential to allow heterogeneous convolutional Fourier classifiers to approach the performance of their fully electronic counterparts and enables data classification on hashed data.

Optimisation of stratified anisotropic media for security films

ABSTRACT Optical security films have gained a lot of attention due to its potential application in authentication services. Electrode-free optical devices are in demand along with electrode devices due to its secure access to the decryption key and ability to hide information from public access. Our concern in this study is the examination of electrode-free optical security film. In such devices, hidden information can be viewed in black/white contrast or controlled birefringent colours, which are produced by patterned phase plate and polariser. In particular, we develop the model of stratified anisotropic media for theoretical description of reflective characteristics of optical security films. Our theoretical results are compared with experimental observations. Blue and yellow birefringent colours of supertwisted nematic liquid crystal cell are achieved by using theory of optical characteristics in anisotropic media and partial coherence. This theoretical analysis suggests new openings in the optimisation of liquid crystal security films.