Full Spectrum Laser Firmware Internal Encryption Error
Abstract
Meta-holographic encryption is a potentially of import technique for information security. Despite rapid progresses in multi-tasked meta-holograms, the number of information channels available in metasurfaces is limited, making meta-holographic encryption vulnerable to some attacking algorithms. Herein, we demonstrate a re-programmable metasurface that can produce capricious holographic images for optical encryption. The encrypted information is divided into two matrices. These two matrices are imposed to the incident lite and the metasurface, respectively. While the all-dielectric metasurface is static, the phase matrix of incident light provides additional degrees of freedom to precisely command the eventual functions at will. With a unmarried Si metasurface, arbitrary holographic images and videos have been transported and decrypted. Nosotros hope that this work paves a more promising style to optical data encryption and authentication.
Introduction
In modern order, almost everything is closely related to the cyberspace currently or in the nigh future. The recent reports of attacks by hackers on the databases evidence that the information security and authentication are more challenging, specially for the large commercial and financial companies
1
. In past decade, many types of optical encryption techniques based on classic and breakthrough optics have been developed to achieve reliable security of data
ii,3
. Attributable to its meaty and not-replicable nature, metasurface-based hologram has gradually been a promising arroyo
4,5,6,seven,eight,9,x
. Metasurface is a kind of two-dimensional materials that has the capability of precisely and fully controlling the incident light
eleven
. By advisedly designing the response of each antenna to dissimilar polarization, incident angle, wavelength, or orbital athwart momentum (OAM), multiple holographic images have been successfully implemented into a single metasurface in the by few years, significantly expanding the capacity and security of information encryption
7,12,13,14,15,sixteen,17,xviii,xix
. Despite of these progresses, the demonstrated meta-holograms are either static or binary
4,5,six,7,8,ix,10,11,12,13,xiv,xv,16,17,18,19,20
. While different multiplexing techniques based on spatial, polarization, wavelength, and OAM accept been combined recently, the number of information channels is even so finite and the electric current record value is only ~2six
(refs.
seven,fifteen,16,17,18,xix,xx,21,22,23,24,25,26
). Similar to the double-random-phase encryption technique, the finite aqueduct number makes the meta-holographic encryption vulnerable to certain attacks because the primal for decryption has to be used repeatedly without frequent update
27
. Therefore, from the point view of information security, it is highly desirable and urgent to realize a meta-hologram with space channels and higher security. Here, nosotros revisit the calorie-free–metasurface interaction and experimentally demonstrate a reprogrammable meta-hologram for optical security and authentication.
Results
Working principle
In principle, the interaction between light and metasurface tin can exist expressed as
28
:
$$U(x,y,z) = {\int\!\!\!\!\!\int} {U_{{\mathrm{inc}}}(x_0,y_0)U_{{\mathrm{meta}}}(x_0,y_0)h(x – x_0,y – y_0,z)} dx_0dy_0,$$
(1)
where
U
inc(x
0,
y
0) and
U
meta(ten
0,
y
0) represent to the functions of incident light and metasurface,
h(x,
y,
z) is an impulse response. The conventional approaches are generally focusing on the response of nanoantennas in metasurface
4,5,6,7,8,9,10,11,12,13,fourteen,15,16,17,eighteen,nineteen
. But few parameters of the incident light take been considered, e.m., polarization and OAM etc.
7,15,sixteen,17,18,xix,20,21,22,23,24,25,26
. Since the metasurface is typically static, the information channel is thus determined by the degrees of incident light and is strongly express
7,15,16,17,18,nineteen,20,21,22,23,24,25,26
. In this research, we divide the required phase profile of a holographic image into two matrices. I matrix is imposed to the metasurface (U
meta(x
0,
y
0)) as earlier, the other one is defined on the incident beam (U
inc(ten
0,
y
0)). This assumption is non but valid for algorithm but also consistent with the modern optical security arrangement, which consists of light source, lens, detectors, phase only masks, and spatial light modulators (SLMs) etc.
29,30
. On one hand, the two-dimensional matrix of incident beam can significantly aggrandize the number of data channels. Even though the metasurface is static, the large matrix of incident beam still has enough large parameters to modify the output beam (U(x,
y,
z)) and the respective holographic images. On the other paw, the dissever information in transported calorie-free and metasurface tin can improve the security. The codes for the modulation of incident light is transported through the cyberspace, whereas the metasurface can be implemented into the final decrypted devices. In case that the transported codes are cracked, they can but produce a random beam without any useful information (see inset in Fig.1b). If the metasurface is stolen and illuminated with an incorrect beam, no information can be hacked or a misleading image could be shown upwardly (Fig.1b). Merely when the modulated incident light matches the metasurface, as shown in Fig.1a, the encrypted image can exist displayed. According to Eq. (i), for encrypted data with fixed overall matrix, the matrices for the incident low-cal and the metasurface can be separated arbitrarily. Consequently, the roles of 2 matrices tin can exist interchanged and the flexibility of the system has been dramatically increased (see Supplementary Fig.2).
a
The schematic of the meta-holographic image with the modulated incident beam.
b
The holographic image of metasurface when information technology is illuminated with an incorrect uniform laser beam. The inset shows that the incident beam itself cannot provide correct information.
Experiments
To test the higher up analysis, nosotros have numerically designed the reprogrammable meta-hologram
31,32
. Taking an paradigm of “HIT 100 (100th ceremony of Harbin Constitute of Technology)”as an instance, the required stage contour for a holographic epitome has been calculated based on Gerchberg–Saxton algorithm. After because both of the efficiency and the fabrication difficulty, the continuous stage contour is discretized into 8-level phase steps (Supplementary Fig.3). And then the discretized matrix is separated into two matrices, which are imposed on the incident axle and the nanoantennas of Si metasurface, respectively (Fig.2a). The phase profile of incident light is controlled by a SLM (UPOLabs-HDSLM80R). The stage only metasurface is fabricated with standard silicon on sapphire wafer via a combined process of electron-beam lithography and reactive ion etching (Supplementary Notesane–3)
32
. Effigy2b
shows the top-view scanning electron microscope (SEM) paradigm of the metasurface. It is equanimous as Si nanopillars with different radius
R. The height of Si nanopillar is fixed at 230 nm. In Fig.2b, viii types of nanopillars with
R = 44, 58, 64, 68, 73, 78, 85, and 95 nm are employed to provide relative loftier transmittance, and precipitous phases from 0 to 7π/4, simultaneously (Supplementary Notes1–3). In this experiment, each phase pixel of Si metasurface in Fig.2b
consists of multiple nanopillars with the same size. This setting is designed to fit the pixel size of Si metasurface and the matrix size of incident light.
a
The designed image, the simulated holographic image, and two separated stage profiles.
b
The top-view SEM of the Si metasurface.
c
Schematic for capturing the meta-hologram.
d
The recorded meta-holographic images with the designed incident beam (left), with a uniform laser beam (centre), and the paradigm of incident light amplification by stimulated emission of radiation itself (right). Hither the lattice size is
L = 240 nm.
The Si metasurface is optically characterized with the setup in Fig.2c. Basically, the linearly polarized laser is generated with a He–Ne laser (633 nm) and a linear polarizer. The light is modulated by the SLM before information technology is focused onto the sample via a 4f organisation. The transmitted hologram is projected onto a screen in the far field and captured with a CCD camera (run across the “Methods” section). Figure2nd
shows the paradigm of intensity distribution generated past the metasurface. Similar to the numerical adding, a “HIT 100” paradigm has been experimentally produced when the Si metasurface is illuminated by the laser beam with the designed stage profile. The calibrated conversion efficiency of the meta-hologram is ~67% (Supplementary Fig.8). For a direct comparison, the aforementioned Si metasurface has also been illuminated with a uniform laser axle. As depicted in the heart panel of Fig.2nd, a misleading blueprint with wrong information is achieved. Similar encryption also holds true for the light source only. The modulated laser beam itself is besides an uniform laser spot with speckles instead of the designed information (correct panel in Fig.2d).
The to a higher place experiments show that the encrypted data tin can be protected even though the key or the metasurface was stolen. For a better demonstration, the vulnerability of the optical encryption scheme has besides been tested with a different key mismatch ratio. Figureiii
summarizes the experimental results equally a function of the modification on incident beam. It is clear to see that the meta-holographic image becomes blurry when the mismatch ratio is >x%. In case of the mismatch ratio exceeds xl%, the “HIT 100” image is close to the noise level and hard to be identified. This ways that the eavesdropper has to steal ~60% of the incident matrix and the last devices, simultaneously to barely recover the encrypted information. This is even higher than the recently demonstrated metasurface-based ghost imaging algorithm
eight
. Annotation that the to a higher place case is valid for the situation that both of the initial positions ((0,0) point of ii matrices and the longitudinal departure from the focal bespeak) and pixel sizes are known, and matched ane another. Without the above information, it shall consume orders of magnitude longer fourth dimension to randomly exam the right central for decryption (Supplementary Figs.6
and
7).
From
a–f, the mismatch ratio of the incident light increases from 0 to 50% with a step of 10%.
In principle, the right key for decryption can still exist hacked if the random test fourth dimension is infinitely long
27
. To avoid the potential attack, the central must be updated frequently. As a upshot, the reprogrammable metasurface is highly desirable for the applications of optical encryption. According to Eq. (1), even though
U
meta(x
0,
y
0) is fixed and known, the displayed holographic image
U(x,
y,
z) can still be changed by controlling the incident light
U
inc(10
0,
y
0). And so the meta-hologram becomes all-optically controllable. In this sense, although the terminal hardware, such as Si metasurfaces are hard to be tuned in pixel level, the precise control of the incident beam can still ofttimes update the keys for decryption. Figure4
summarizes the experimental demonstration of the all-optically reprogrammable meta-hologram. In this experiment, the Si metasurface is kept as the aforementioned i as Fig.2b. By just modifying the phase distributions of the incident light, the displayed holographic epitome becomes an image of hydrogen element “H”, which is totally unlike from the image of “HIT 100” in Fig.2. With the further modification on incident light, the displayed hologram can be switched to an image of hydrogen element or whatsoever other elements. With the continuous change of incident light, nosotros have experimentally realized the holographic images of the entire periodic tabular array of the elements, with 118 types of elements. Here, each element is an individual holographic image produced by the same metasurface. The periodic table of elements is a clear demonstration of the programmable and all-optically controllable meta-hologram.
The holographic images of periodic chemical element table. Each element in this table is one holographic image that is generated with the same metasurface in Fig.2.
We note that the number of periodic element table is not the limit of the information channel of our design. With the same Si metasurface, we basically can realize arbitrarily shaped holographic images, including the holographic paradigm with complicated contents (Supplementary Fig.x). To verify this possibility, we take too produced a set of holographic images by modulating the incident beam and plotted them in Supplementary Fig.11. Each panel corresponds to one frame of a pinball archetype game. By playing these frames sequentially, a video of the pinball game from commencement to the end has too been achieved (Supplementary Movie1). These results farther demonstrate the potential of the proposed technique in the transportation of videos as well, significantly expanding the potential applications of metasurface holograms.
Give-and-take
In summary, we have revisited the light–metasurface interaction and experimentally realized the reprogrammable meta-hologram. By separating the designed phase profile to 2 matrices, and defining them to incident laser and metasurface, we observe that the lack of pixel-level control of metasurface in optical frequency range can be made up via the all-optical control. With the phase command of incident axle, we have experimentally demonstrated that a single metasurface tin can display capricious holographic images, too every bit encrypted videos. This technique shall notice its applications in data security and authentication. It also paves a promising step toward dynamic displays as well.
Methods
The numerical simulation
The silicon metasurface was numerically imitation with a commercial software COMSOL Multiphysics. The Si nanorods are placed on a sapphire substrate with refractive indices of iii.88 and 1.76 at 633 nm. The height of nanorod was kept at 230 nm. The radius of nanorod and the lattice size are
R
and
L, respectively. Periodic purlieus conditions were applied in horizontal direction to mimic the periodic structure, and perfectly matched layers were used to absorb the transmission and reflection waves. The details are shown in Supplementary Notes1
and
2.
The fabrication of Si metasurface
The Si metasurfaces were fabricated past a combined process of electron-beam lithography and reactive ion etching. The 230 nm single-crystal silicon film on a sapphire wafer was cleaned with acetone and coated with 100 nm electron-beam resist polymethyl methacrylate. The sample was baked at 180 °C for one h and and then patterned by electron-beam writer (Raith E-line) with a dose xc µC/cmii
under an dispatch voltage xxx kV. Afterward developing with MIBK&IPA (ane:three) solution, 15 nm Cr was deposited on the sample using E-beam evaporation (SKE_A_75), and Cr hard mask was realized via a liftoff process in remover PG solution (Micro Chem) for 24 h. The blueprint was transferred to the Si through reactive ion etching with SF6
and CHF3
in Oxford Plasmalab Arrangement 100. The vacuum caste was 10−5
and the gas flow was 5 and l sccm for SF6 and CHF3, respectively. Finally, the Si metasurfaces were obtained past removing the Cr mask in Cr etchant solution (Aldrich Chemical science) for 30 min.
The optical label
During the optical characterization, the alignment of the phases in incident beam the phases in metasurface is crucial. The light is modulated past the SLM before information technology is focused onto the sample via a 4f system. The transmitted hologram is projected onto a screen in the far field and captured with a CCD camera. The SLM is switched to intensity module to clearly seen the focused axle, and precisely match it with the metasurface. Then it is switched dorsum to stage module and mensurate the meta-hologram.
Data availability
The data that support the findings of this report are available on asking from the respective authors.
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Acknowledgements
This research was supported past the National Key Research and Development Projection (Grant No. 2018YFB2200403), National Natural Science Foundation of China (Grant Nos. 11974092, 91850204, 11934012, and 61975041), Shenzhen Fundamental research projects (Grant No. JCYJ20180507184613841, JCYJ20180507183532343, and JCYJ20180306172041577), Shenzhen engineering laboratory on organic–inorganic perovskite devices, and the Primal Research Funds for the Central Universities. The authors also acknowledge fiscal support from Shenzhen Scientific discipline and Technology Innovation Commission (No. SGDX2019081623281169). The authors are grateful to the Department of Electronic and Data Engineering science, The Hong Kong Polytechnic University for their support likewise.
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Due south.X. and D.P.T. conceived the idea and supervise the research. Yard.Q. performed the device designs and experimental measurements. Due west.Y. and Y.50. helped the fabrication of nanostructures. Q.S., C.-W.Q. and J.H. analyzed the results. All the authors discussed the contents and prepared the manuscript.
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Cite this article
Qu, M., Yang, West., Song, Q.
et al.
Reprogrammable meta-hologram for optical encryption.
Nat Commun
11,
5484 (2020). https://doi.org/10.1038/s41467-020-19312-9
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https://doi.org/10.1038/s41467-020-19312-ix
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