Open Access
Add to BibSonomy
Abstract
Plasmonic color generation based on gap-plasmon resonators finds an increasing role in subwavelength fade-free color printing, data storage and information encoding due to its high spatial resolution and mechanical/chemical stability. However, most of the current designs are limited to trivial spectral responses, leading to subtractive colors with restricted ranges of their color palettes. Here, we design a plasmonic color metasurface made of an aluminum resonator array, producing strong gap plasmon resonance and nearly perfect light absorption that results in enhanced color saturation. The range of color palette is broadly increased by introducing polarization-dependent supercell of plasmonic resonators, forming “i-patterned” dimers. Such a plasmonic color metasurface holds a great promise for color displays, polarization-multiplexing system, image encryption, and steganography.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Color arises from the spectral reshaping of scattered field of the broadband light source due to light-matter interaction. Along with natural sources of colors [1,2], one of the possible ways of producing vivid colors is to use dyes and pigments [3], which offer vibrant coloration irrespective of illumination condition and viewing angles. However, some of the synthetic dyes are composed of toxic materials and may easily bleach when exposed to intense ultraviolet (UV) illumination. In recent decades, the engineering of electromagnetic (EM) waves by plasmonic metasurface has been the subject of studies ranging from microwave [4] to infrared/optical light [5–9]. Strong confinement and enhancement of EM fields enable such metasurface exhibit unique features including light absorption [10–12], subdiffraction focusing [13] and bio-medical sensing [14]. Plasmonic metasurfaces exploit the resonant interaction of electromagnetic fields with elementary building blocks - plasmonic resonators – that offer a possibility to tailor the spectral shape of transmitted/reflected light.
Recently, it has also been demonstrated that plasmonic metasurfaces can be used to produce structural colors [15–25]. High spatial resolution [26], mechanical/chemical robustness [22] and immunity to chromic degradation [27] make such plasmonic color metasurface (PCM) more attractive platform than dyes and pigments for the synthesis of artificial colors that are stable, environmentally friendly and fade-free. Because the resonant frequency of a plasmonic particle is highly dependent on its environment and geometry, some plasmonic color filters can only produce a single color when the geometry of the resonators is fixed [15,16,18–23,26–30]. Moreover, the inherent loss of plasmonic resonators and the limited range of spectra available to adjustment by varying resonators’ dimensions restrain the diversity of the generated colors. By using laser post-writing [31] and chemical reaction [32], advanced optical applications such as switchable displays, cryptography, and camouflage can be realized. However, the laser-induced reshaping of the resonators is not reversible and the response time of chemical reaction is relatively slow.
Following our initial experiments in this area [33] and related critical efforts [22,26], we employ an array of gap plasmon resonators (GPRs) for color generation. The uppermost metal layer is an array of square shaped aluminum (Al) resonators, separated from the Al back reflector by a thin (20 nm) silicon dioxide (SiO2) spacer. Al is chosen due to its broadband plasmonic properties with the wavelengths ranging from the UV to the near-infrared region, associated with the low cost, sustainability, and long-term stability [34,35]. The proposed metasurface is capable of achieving nearly perfect absorption since the electric field of the generated gap-plasmon is almost completely confined inside the metal-insulator-metal (MIM) resonator. The absorption peak position can be tuned throughout the entire visible spectral range (400 nm - 750 nm) by varying the width of the resonators, allowing for the generation of a complete set of subtractive colors (CMY - cyan, magenta and yellow). Furthermore, the range of color palette can be extended to the additive primary colors (RGB - red, green and blue) by introducing polarization-dependent supercells arranged of a centrosymmetric pair of i-patterned dimers. Here we show that it is possible to achieve full-color generation with high saturation level, along with a dramatic reduction of “cross-talk effect” between structural elements of PCM [36]. These findings enable unparalleled control over the metasurface absorption bands by tuning the polarization angle of incident light. The proposed plasmonic color nanostructures could be of crucial utility for designing encrypted color tags [37], dynamically tunable color displays [38,39], high-density data storage [40], and polarization multiplexed systems [41–44].
2. Results and discussion
Figure 1(a) illustrates the design of the PCM consisting of three functional layers, including the top 30 nm-thick Al resonator array, a 20 nm-thick SiO2 spacer and an Al back reflector. The width of the resonators (w) is varied to generate different colors while the periodicity of the array with square lattice is fixed to 200 nm. All simulations are done by using a commercial finite element method solver (CST Studio 2017). One basic element of the PCM is analyzed to obtain the reflectance and absorbance. Here, we assume that incident wave is travelling along z-45axis, while metasurface is assumed to be infinite along x and y directions. The permittivities of Al and SiO2 are obtained from [45] and [46], respectively. In a fabrication process, the dielectric function of Al film depends on the residual gases in the chamber and the deposition rate [47]. By optimizing the fabrication conditions, the surface roughness of the deposited Al film was controlled well within 0.6 nm, hence ensuring a good agreement between the dielectric function of the experimental Al film and Palik data [45] that we use.
Fig. 1 (a) Schematic diagram of the metasurface based on gap plasmon resonator arrays. The thicknesses of the top layer hm and insulator spacer hd are fixed to 30 nm and 20 nm, respectively. The periodicity of the array is 200 nm. (b) Simulated optical absorption spectra of the metasurface with varying widths of the resonator w (65 nm, 85 nm, and 110 nm). (c) Cross-section view of electric and magnetic field distribution at wavelengths of 445 nm, 532 nm and 665 nm, corresponding to the three absorption spectra positions in (b).
The absorption plots in the visible range (400 nm - 750 nm) for three different widths of the resonator (w = 65 nm, 85 nm, and 110 nm) are presented in Fig. 1(b). Resonance condition for GPRs is related to the width w of the resonator and the effective mode index of gap surface plasmon [22,48], hence the absorption spectra position can thereby be tailored by changing the width w of plasmonic resonator. By properly choosing the dimensions of the resonator, nearly perfect optical absorption can be achieved at 445 nm, 532 nm and 665 nm, leading to different absorption spectra, which in turn generate yellow, magenta and cyan colors [29]. Color generation is explained in more details below. Figure 1(c) shows that the gap surface plasmon is produced by a magnetic dipole resonance mode. A strong electric field enhancement can be observed at the boundaries of the resonator while the maximum of the magnetic field is found in the gap.
To illustrate the visual color performance of the proposed PCM, a variety of reflectance spectra simulated at normal incidence are plotted in Fig. 2(a). As expected, the resonant dip in the reflectance spectra is red-shifted from 420 nm to 665 nm as the resonator width w increases from 60 nm to 110 nm in steps of 5 nm. The corresponding visual performances of each reflectance spectrum are presented in color insets on the right side of each spectrum. All the colors in the insets are calculated according to the RGB values transferred from their spectral data and color-matching functions defined by the International Commission on Illumination (CIE). The tristimulus values X, Y and Z are computed according to the following equations [32]:
Here, (λ), (λ), and (λ) are the standard observer functions defined by CIE. The integrals are computed across the entire visible range. I(λ) is the relative spectral power distribution of the incident light. R(λ) is the simulated reflectance spectra. K is the normalizing constant and can be calculated as . Then, the chromaticity coordinates (x, y) in CIE 1931 color space can be obtained by using the following equations:Fig. 2 (a) Left panel: Simulated reflectance spectra of the metasurface as the width of the aluminum (Al) resonator increases from 60 nm to 110 nm with a step of 5 nm. Right panel: a broad palette of subtractive colors calculated from the corresponding reflectance spectra. (b) Chromaticity coordinates corresponding to the simulated spectra.
When a given color is fully saturated, the corresponding chromaticity coordinates (x, y) are located at the outer horseshoe-shaped edge of the CIE 1931 diagram. Conversely, the central white point corresponds to the completely unsaturated color. It can be concluded that the color saturation can be understood intuitively by the distance between chromaticity coordinates (x, y) and the outer edge of the CIE 1931 diagram.
Figure 2(b) presents the chromaticity coordinates (x, y) corresponding to the reflected spectra of the proposed PCM by changing the width of the Al resonator. A broader palette of subtractive colors are generated with higher saturation compared to some recent works [29,49,50]. However, the output color would remain fixed once the Al resonator is fabricated, and RGB colors would be still not achievable.
To address the problem of static color generation, we propose the concept of anisotropic plasmonic color metasurface (APCM) by introducing polarization-dependent plasmonic resonators. Figure 3(a) shows a schematic diagram of the GPRs in a single supercell. This updated basic element consists of a pair of centrosymmetric i-patterned dimers. Each i-patterned dimer is combined of a square-shaped resonator and a rectangular-shaped resonator. The periodicity of the supercell is 400 nm. In contrast to the square resonators which are polarization-independent, rectangular resonators exhibit gap surface plasmon resonances at different wavelengths for x- and y- polarized light. As previously analyzed, the resonant absorption of the metasurface is determined by the width of the resonator along the incident polarization. As a result, distinct colors can be generated under orthogonal polarizations. Figure 3(b) shows the simulated reflectance spectra when the x- polarized light illuminates the APCM at normal incidence. The corresponding visual color performance is illustrated with three square color insets. The red, green and blue colors are obtained when the length and width (l, w) of the rectangular resonators are (85 nm, 65 nm), (110 nm, 65 nm) and (110 nm, 85 nm), respectively. The spectral response of the additive colors results from simultaneously creating two narrowband absorption peaks to form a broader absorption band. For example, blue colored light will be reflected from the APCM when the two resonators in one i-patterned dimer are designed to absorb green (w = 85 nm) and red light (l = 110 nm).
Fig. 3 (a) Schematic diagram of the supercell of the anisotropic plasmonic color metasurface. The supercell consists of a pair of centrosymmetric i-patterned dimers. Each i-patterned dimeris combined of a square shaped resonator and a rectangular shaped resonator. (b) Simulated reflectance spectra of the updated metasurface with varying widths and lengths (w, l) of the rectangular resonators (85 nm, 65 nm), (110 nm, 65 nm) and (110 nm, 85 nm). The three insets show the calculated colors of the corresponding spectral responses.
In order to have an insight into the visual color performance of the APCM, length and width of the resonators are changed from 65 to 105 nm with a step of 10 nm to investigate the full palette of colors that can be achieved. Simulated colors under y- polarized and x- polarized light are presented in Figs. 4(a) and 4(b), respectively. The square and rectangular shaped resonators exhibit the same dimension along y- direction. Therefore, the generated colors are mainly determined by the width w and the color palette is limited to a range of subtractive colors shown by the black curve in Fig. 4(c). For x- polarized illumination, a broader palette of colors can be achieved since both the length l and width w of the resonators influence the generated colors. In this case, APCM is capable of tuning two absorption bands of the visible spectrum thus reflecting the remaining to render colors. The white curve in Fig. 4(c) shows the color palette achieved by APCM upon x-polarized illumination. It can be observed that not only full-color generation is realized, but also the color saturation is increased. Additionally, this APCM can select the generated colors by rotating the polarizer. Multiple distinct colors can be simultaneously encoded in each pixel, providing promising avenues for applications in the polarization-multiplexing system [41,42], stereoscopic prints [36], and optical imaging encryption [38].
Fig. 4 (a), (b) Simulated color results of the anisotropic plasmonic color metasurface under (a) y- and (b) x-polarized illumination. (b) Chromaticity coordinates corresponding to the simulated spectra. The black and white curves show the color palette achieved by the metasurface upon y- and x-polarized illumination, respectively.
In the polarization-multiplexing color display system, the undesired mixing of the overlaid images between different polarizations (also known as “cross-talk” effect [36]) is a challenging problem which breaks the visual homogeneity and causes parasitic distortion of the encoded image information. Fortunately, the “cross-talk” effect can be reduced by using GPRs-based metasurface since the resonance bands are determined by the dimension of the resonators aligned along the incident polarization. As shown in Fig. 4(a), in contrast to y-polarized illumination along the direction in which the width of the rectangular resonator w is varied, we observe that the generated colors remains almost intact when l varies with w being fixed. For example, the five color images in each horizontal row are too similar to be distinguishable by the naked eye.
To show the APCM’s promising potentials to be used in switchable color display, we simulate a design of a “7-segment display” pattern of which the numbers can be altered by the incident polarization as shown in Figs. 5(a) and 5(b). This pattern is composed of three different types of supercells, which are labeled by numbers “I, II and III” and variant gray scales. Region I and II are occupied by orthogonally placed supercells consisting of a pair of i-patterned dimers in reverse direction. Based on the results in Figs. 4(a) and 4(b), these pixels exhibit polarization-dependent visual performance. Region III, occupied by square shaped Al resonator array, will constantly render a static color for the background. Resonators with the dimension (l = 105 nm, w = 85 nm) are chosen to generate colors with no significant “cross-talk” effect. For x- polarized illumination, a number “3” emerges in in blue color in distinct contrast to the magenta background. Another number “1” occurs when the incident polarization is rotated by 90°. Interestingly, there is no obvious overlaid image or color deviation between these two displays. This visual homogeneity benefits from the fact that magenta colors generated by different types of supercells exhibit nearly the same saturation. In addition, a number “8” is observed when the incident light is diagonally polarized with the orientation of the resonator’s axis. This property enables the encoding of more than two distinct color information states in the same area, opening a promising avenue for encryption and steganography.
Fig. 5 (a) Overview of a “7-segment display” pattern with three different types of supercells. (b) Simulated color display upon different incident polarizations. Different information states can be clearly revealed with reduced “cross-talk” effect.
3. Conclusion
In this work, we proposed a plasmonic color metasurface consisting of aluminum gap plasmon resonators. As the electric field of the incident light is strongly confined in the gap, nearly perfect absorption is achieved in the visible spectral region. The absorption band can be tuned by changing the width of the resonators, leading to a broad palette of highly saturated subtractive colors. By introducing supercells consisting of a pair of centrosymmetric i-patterned resonators, gap surface plasmon resonance bands can be adjusted thus enabling full-color generation. Color saturation is increased since the reflection peaks are tailored to be narrower and sharp. Furthermore, variously oriented resonators and different incident polarizations can be used as the additional degrees of freedom for switchable color display with reduced “cross-talk” effect. Such a polarization multiplexing metasurface could advance tremendous potential applications such as security certification, high-density data storage, encryption, and steganography.
Funding
Chinese Scholarship Council (CSC, No. 201606050044); National Natural Science Foundation of China (No. 61575032); Air Force Office of Scientific Research MURI Grant (FA9550-14-1-0389); DARPA/DSO Extreme Optics and Imaging (EXTREME) program (HR00111720032).
References
1. P. Vukusic and J. R. Sambles, “Photonic structures in biology,” Nature 424(6950), 852–855 (2003). [CrossRef] [PubMed]
2. S. Kinoshita and S. Yoshioka, “Structural Colors in Nature: The Role of Regularity and Irregularity in the Structure,” ChemPhysChem 6(8), 1442–1459 (2005). [CrossRef] [PubMed]
3. Y. Huo, C. C. Fesenmaier, and P. B. Catrysse, “Microlens performance limits in sub-2µm pixel CMOS image sensors,” Opt. Express 18(6), 5861–5872 (2010). [CrossRef] [PubMed]
4. S. Furukawa, T. Masui, and N. Imanaka, “Synthesis of new environment-friendly yellow pigments,” J. Alloys Compd. 418(1–2), 255–258 (2006). [CrossRef]
5. M. Pu, C. Hu, M. Wang, C. Huang, Z. Zhao, C. Wang, Q. Feng, and X. Luo, “Design principles for infrared wide-angle perfect absorber based on plasmonic structure,” Opt. Express 19(18), 17413–17420 (2011). [CrossRef] [PubMed]
6. M. Song, H. Yu, J. Luo, and Z. Zhang, “Tailoring Infrared Refractory Plasmonic Material to Broadband Circularly Polarized Thermal Emitter,” Plasmonics 12(3), 649–654 (2017). [CrossRef]
7. X.-G. Luo, M.-B. Pu, X. Li, and X.-L. Ma, “Broadband spin Hall effect of light in single nanoapertures,” Light Sci. Appl. 6(6), e16276 (2017). [CrossRef] [PubMed]
8. J. Zhang, J.-Y. Ou, K. F. MacDonald, and N. I. Zheludev, “Optical response of plasmonic relief meta-surfaces,” J. Opt. 14(11), 114002 (2012). [CrossRef]
9. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature 391(6668), 667–669 (1998). [CrossRef]
10. M. Song, H. Yu, C. Hu, M. Pu, Z. Zhang, J. Luo, and X. Luo, “Conversion of broadband energy to narrowband emission through double-sided metamaterials,” Opt. Express 21(26), 32207–32216 (2013). [CrossRef] [PubMed]
11. Y. Wang, M. Song, M. Pu, Y. Gu, C. Hu, Z. Zhao, C. Wang, H. Yu, and X. Luo, “Staked Graphene for Tunable Terahertz Absorber with Customized Bandwidth,” Plasmonics 11(5), 1201–1206 (2016). [CrossRef]
12. W. Li, U. Guler, N. Kinsey, G. V. Naik, A. Boltasseva, J. Guan, V. M. Shalaev, and A. V. Kildishev, “Refractory Plasmonics with Titanium Nitride: Broadband Metamaterial Absorber,” Adv. Mater. 26(47), 7959–7965 (2014). [CrossRef] [PubMed]
13. M. Song, C. Wang, Z. Zhao, M. Pu, L. Liu, W. Zhang, H. Yu, and X. Luo, “Nanofocusing beyond the near-field diffraction limit via plasmonic Fano resonance,” Nanoscale 8(3), 1635–1641 (2016). [CrossRef] [PubMed]
14. N. S. King, L. Liu, X. Yang, B. Cerjan, H. O. Everitt, P. Nordlander, and N. J. Halas, “Fano Resonant Aluminum Nanoclusters for Plasmonic Colorimetric Sensing,” ACS Nano 9(11), 10628–10636 (2015). [CrossRef] [PubMed]
15. T. Xu, Y.-K. Wu, X. Luo, and L. J. Guo, “Plasmonic nanoresonators for high-resolution colour filtering and spectral imaging,” Nat. Commun. 1(5), 59 (2010). [CrossRef] [PubMed]
16. S. J. Tan, L. Zhang, D. Zhu, X. M. Goh, Y. M. Wang, K. Kumar, C.-W. Qiu, and J. K. W. Yang, “Plasmonic Color Palettes for Photorealistic Printing with Aluminum Nanostructures,” Nano Lett. 14(7), 4023–4029 (2014). [CrossRef] [PubMed]
17. A. Kristensen, J. K. W. W. Yang, S. I. Bozhevolnyi, S. Link, P. Nordlander, N. J. Halas, and N. A. Mortensen, “Plasmonic colour generation,” Nat. Rev. Mater. 2(1), 16088 (2017). [CrossRef]
18. V. R. Shrestha, S.-S. Lee, E.-S. Kim, and D.-Y. Choi, “Aluminum Plasmonics Based Highly Transmissive Polarization-Independent Subtractive Color Filters Exploiting a Nanopatch Array,” Nano Lett. 14(11), 6672–6678 (2014). [CrossRef] [PubMed]
19. V. R. Shrestha, C.-S. Park, and S.-S. Lee, “Enhancement of color saturation and color gamut enabled by a dual-band color filter exhibiting an adjustable spectral response,” Opt. Express 22(3), 3691–3704 (2014). [CrossRef] [PubMed]
20. J. S. Clausen, E. Højlund-Nielsen, A. B. Christiansen, S. Yazdi, M. Grajower, H. Taha, U. Levy, A. Kristensen, and N. A. Mortensen, “Plasmonic Metasurfaces for Coloration of Plastic Consumer Products,” Nano Lett. 14(8), 4499–4504 (2014). [CrossRef] [PubMed]
21. M. Miyata, H. Hatada, and J. Takahara, “Full-Color Subwavelength Printing with Gap-Plasmonic Optical Antennas,” Nano Lett. 16(5), 3166–3172 (2016). [CrossRef] [PubMed]
22. A. S. Roberts, A. Pors, O. Albrektsen, and S. I. Bozhevolnyi, “Subwavelength Plasmonic Color Printing Protected for Ambient Use,” Nano Lett. 14(2), 783–787 (2014). [CrossRef] [PubMed]
23. H. Wang, X. Wang, C. Yan, H. Zhao, J. Zhang, C. Santschi, and O. J. F. Martin, “Full Color Generation Using Silver Tandem Nanodisks,” ACS Nano 11(5), 4419–4427 (2017). [CrossRef] [PubMed]
24. F. Cheng, J. Gao, T. S. Luk, and X. Yang, “Structural color printing based on plasmonic metasurfaces of perfect light absorption,” Sci. Rep. 5(1), 11045 (2015). [CrossRef] [PubMed]
25. A. M. Shaltout, J. Kim, A. Boltasseva, V. M. Shalaev, and A. V. Kildishev, “Ultrathin and multicolour optical cavities with embedded metasurfaces,” Nat. Commun. 9(1), 2673 (2018). [CrossRef] [PubMed]
26. K. Kumar, H. Duan, R. S. Hegde, S. C. W. Koh, J. N. Wei, and J. K. W. Yang, “Printing colour at the optical diffraction limit,” Nat. Nanotechnol. 7(9), 557–561 (2012). [CrossRef] [PubMed]
27. T. D. James, P. Mulvaney, and A. Roberts, “The Plasmonic Pixel: Large Area, Wide Gamut Color Reproduction Using Aluminum Nanostructures,” Nano Lett. 16(6), 3817–3823 (2016). [CrossRef] [PubMed]
28. G. Si, Y. Zhao, J. Lv, M. Lu, F. Wang, H. Liu, N. Xiang, T. J. Huang, A. J. Danner, J. Teng, and Y. J. Liu, “Reflective plasmonic color filters based on lithographically patterned silver nanorod arrays,” Nanoscale 5(14), 6243–6248 (2013). [CrossRef] [PubMed]
29. W. Sabra, S. I. Azzam, M. Song, M. Povolotskyi, A. H. Aly, and A. V. Kildishev, “Plasmonic metasurfaces for subtractive color filtering: optimized nonlinear regression models,” Opt. Lett. 43(19), 4815–4818 (2018). [CrossRef] [PubMed]
30. W. Yue, S. Gao, S.-S. Lee, E.-S. Kim, and D.-Y. Choi, “Highly reflective subtractive color filters capitalizing on a silicon metasurface integrated with nanostructured aluminum mirrors,” Laser Photonics Rev. 11(3), 1600285 (2017). [CrossRef]
31. X. Zhu, C. Vannahme, E. Højlund-Nielsen, N. A. Mortensen, and A. Kristensen, “Plasmonic colour laser printing,” Nat. Nanotechnol. 11(4), 325–329 (2016). [CrossRef] [PubMed]
32. X. Duan, S. Kamin, and N. Liu, “Dynamic plasmonic colour display,” Nat. Commun. 8, 14606 (2017). [CrossRef] [PubMed]
33. W. Cai, U. K. Chettiar, H.-K. Yuan, V. C. de Silva, A. V. Kildishev, V. P. Drachev, and V. M. Shalaev, “Metamagnetics with rainbow colors,” Opt. Express 15(6), 3333–3341 (2007). [CrossRef] [PubMed]
34. D. Gérard and S. K. Gray, “Aluminium plasmonics,” J. Phys. D Appl. Phys. 48(18), 184001 (2015). [CrossRef]
35. J. Olson, A. Manjavacas, L. Liu, W. S. Chang, B. Foerster, N. S. King, M. W. Knight, P. Nordlander, N. J. Halas, and S. Link, “Vivid, full-color aluminum plasmonic pixels,” Proc. Natl. Acad. Sci. U.S.A. 111(40), 14348–14353 (2014). [CrossRef] [PubMed]
36. X. M. Goh, Y. Zheng, S. J. Tan, L. Zhang, K. Kumar, C.-W. Qiu, and J. K. W. Yang, “Three-dimensional plasmonic stereoscopic prints in full colour,” Nat. Commun. 5(1), 5361 (2014). [CrossRef] [PubMed]
37. J. Li, S. Kamin, G. Zheng, F. Neubrech, S. Zhang, and N. Liu, “Addressable metasurfaces for dynamic holography and optical information encryption,” Sci. Adv. 4(6), r6768 (2018). [CrossRef] [PubMed]
38. M. Song, X. Li, M. Pu, Y. Guo, K. Liu, H. Yu, X. Ma, and X. Luo, “Color display and encryption with a plasmonic polarizing metamirror,” Nanophotonics 7(1), 323–331 (2018). [CrossRef]
39. M. Song, A. V. Kildishev, D. Wang, Z. Wang, Y. Xuan, A. Boltasseva, H. Yu, and V. M. Shalaev, “Wavelength-dependent Optical-rotation Manipulation for Active Color Display and Highly Secure Encryption,” in Conference on Lasers and Electro-Optics, OSA Technical Digest (Online) (OSA, 2018), p. FTh4M.2. [CrossRef]
40. E. Heydari, J. R. Sperling, S. L. Neale, A. W. Clark, and H. Esmaeil, “Plasmonic color filters as dual-state nanopixels for high-density microimage encoding,” Adv. Funct. Mater. 27(35), 1701866 (2017). [CrossRef]
41. T. Ellenbogen, K. Seo, and K. B. Crozier, “Chromatic plasmonic polarizers for active visible color filtering and polarimetry,” Nano Lett. 12(2), 1026–1031 (2012). [CrossRef] [PubMed]
42. Z. Li, A. W. Clark, and J. M. Cooper, “Dual color plasmonic pixels create a polarization controlled nano color palette,” ACS Nano 10(1), 492–498 (2016). [CrossRef] [PubMed]
43. X. Zhu, S. Xiao, L. Shi, X. Liu, J. Zi, O. Hansen, and N. A. Mortensen, “A stretch-tunable plasmonic structure with a polarization-dependent response,” Opt. Express 20(5), 5237–5242 (2012). [CrossRef] [PubMed]
44. E. Højlund-Nielsen, X. Zhu, M. S. Carstensen, M. K. Sørensen, C. Vannahme, N. Asger Mortensen, and A. Kristensen, “Polarization-dependent aluminum metasurface operating at 450 nm,” Opt. Express 23(22), 28829–28835 (2015). [CrossRef] [PubMed]
45. E. D. Palik, Handbook of Optical Constants of Solids (Elsevier, 1985).
46. G. Ghosh, “Dispersion-equation coefficients for the refractive index and birefringence of calcite and quartz crystals,” Opt. Commun. 163(1–3), 95–102 (1999). [CrossRef]
47. K. M. McPeak, S. V. Jayanti, S. J. P. Kress, S. Meyer, S. Iotti, A. Rossinelli, and D. J. Norris, “Plasmonic films can easily be better: rules and recipes,” ACS Photonics 2(3), 326–333 (2015). [CrossRef] [PubMed]
48. F. Ding, Y. Yang, R. A. Deshpande, and S. I. Bozhevolnyi, “A review of gap-surface plasmon metasurfaces: fundamentals and applications,” Nanophotonics 7(6), 1129–1156 (2018). [CrossRef]
49. F. Chen, S.-W. Wang, X. Liu, R. Ji, Z. Li, X. Chen, Y. Chen, and W. Lu, “Colorful solar selective absorber integrated with different colored units,” Opt. Express 24(2), A92–A103 (2016). [CrossRef] [PubMed]
50. R. J. H. Ng, X. M. Goh, and J. K. W. Yang, “All-metal nanostructured substrates as subtractive color reflectors with near-perfect absorptance,” Opt. Express 23(25), 32597–32605 (2015). [CrossRef] [PubMed]
