Plasmonic Color Filters as Dual‐State Nanopixels for High‐Density Microimage Encoding

Abstract

Plasmonic color filtering has provided a range of new techniques for "printing" images at resolutions beyond the diffraction-limit, significantly improving upon what can be achieved using traditional, dye-based filtering methods. Here, a new approach to high-density data encoding is demonstrated using full color, dual-state plasmonic nanopixels, doubling the amount of information that can be stored in a unit-area. This technique is used to encode two data sets into a single set of pixels for the first time, generating vivid, near-full sRGB (standard Red Green Blue color space)color images and codes with polarization-switchable information states. Using a standard optical microscope, the smallest "unit" that can be read relates to 2 × 2 nanopixels (370 nm × 370 nm). As a result, dual-state nanopixels may prove significant for long-term, high-resolution optical image encoding, and counterfeit-prevention measures. over their microscale, dye-based counterparts. Chief among these are their subwavelength dimensions (leading to ultradense, ultrathin pixel arrays), and their long-term environmental stability (they do not degrade or fade over time due to radiation exposure). As a result, plasmonic filters have been positioned as new technological solutions for subwavelength color printing, [1,4,[7][8][9]12] anticounterfeiting measures, [19,20] and RGB splitting for image sensors; [2,17,21,22] thus representing one of the most promising, technologically relevant areas of current plasmonic research activity. Here, we explore a new application of polarizationcontrolled plasmonic filters: dual output, full-color optical image encoding. Recent developments in the engineering and manipulation of materials on the nanoscale have given rise to a number of new techniques with the potential for physically encoding data and images into optically readable volumes and surfaces. [23,24] Using semiconductor quantum dots, [25][26][27] graphene, [28] and various super-resolution lithography techniques, [29][30][31][32][33][34] researchers are demonstrating novel 2D and 3D techniques that may enable the next generation of optical storage and encoding technologies. Plasmonic particles and filters have also seen applications in these research areas, with the aforementioned image encoding examples having been joined by demonstrations of their use in optical data storage. [23,24,[35][36][37] Here, we show a new utilization of image encoding using polarization multiplexed plasmonic filters, where, unlike previous studies that employed color or position switching in fixed images, [14,38] we show that two arbitrary, full-color images can be encoded into a single array of pixels. Our individual pixels are comprised of asymmetric cross-shaped nanoapertures in a thin film of aluminum. Each aperture is engineered to exhibit two independent plasmonic resonances which can be tuned across the sRGB (standard Red Green Blue) color-space (a single pixel can be encoded with any two arbitrary colors). We go on to show that by using the smallest visible unit ...

Flexible, Large‐Area Covert Polarization Display Based on Ultrathin Lossy Nanocolumns on a Metal Film

“…Recently developed concepts in structural color open up opportunities for future applications including nanocolor painting, chiral reflectors/filters, and digital microdisplays . Together with these possibilities, compared to conventional dyes/pigments, structural colors have improved potential for fine‐tunability of color achieved by controlling their dimensions, as well as for sustainable production, and durability.…”

“…Each of these capabilities also facilitates the creation of security features for anti‐counterfeiting. Some of the most successful demonstrations of structural color involve 3D chiral color prints, surface plasmon‐mediated optical recording, covert images from plasmonic cavities, etc. Printed/engraved images or codes using such specialized optical media can only be retrieved if the physical structure in every zone is completely known a priori.…”

“…Since most of these methods use dielectric/metallic nanostructures that resonate at a particular wavelength or for a particular polarization of light, in order to improve the optical performance, much attention has recently been paid to geometrical optimization and/or material selection . The reported experimental demonstrations are mainly achieved by elaborate processes (using e‐beam lithography or focused ion beam lithography) to define arrays of nanopatterns, however, practical use of such processes is restricted to overall lateral dimensions of less than a few millimeters.…”

Electrochromic‐Polymer‐Based Switchable Plasmonic Color Devices Using Surface‐Relief Nanostructure Pixels

“…

Plasmonic colors are structural colors generated by the resonant interaction of light with metallic nanostructures through surface plasmons. [13] The potentials of applying plasmonic colors in active displays have been increasingly recognized and various novel device configurations implementing plasmonic colors have been demonstrated, such as metal-nanostructures-array-based color filters for imaging devices, [14][15][16] metal-insulator-metal resonators tuned by modulating refractive index, [17,18] plasmonic color substrates controlled by liquid crystals, [19][20][21] electrochromically switchable plasmonic color devices, [22][23][24] plasmonic colors operated via reversible electrodeposition, [25,26] and aluminum nano-antenna arrays for high-chromaticity color filters in displays. [13] The potentials of applying plasmonic colors in active displays have been increasingly recognized and various novel device configurations implementing plasmonic colors have been demonstrated, such as metal-nanostructures-array-based color filters for imaging devices, [14][15][16] metal-insulator-metal resonators tuned by modulating refractive index, [17,18] plasmonic color substrates controlled by liquid crystals, [19][20][21] electrochromically switchable plasmonic color devices, [22][23][24] plasmonic colors operated via reversible electrodeposition, [25,26] and aluminum nano-antenna arrays for high-chromaticity color filters in displays.

…”

Active Color Control in a Metasurface by Polarization Rotation

“…Nevertheless, dynamic color printing can be realized in a far simpler system by polarization control without involving any external stimuli [30][31][32]. A periodic array of cross-shaped nanoantennas [8,[33][34][35], elliptical nanostructures [31,32,36], rectangle nanostructures [37] and a grating pattern [38] have demonstrated active color printing by rotating incident polarization. Here, lack of four-fold symmetry leads to active color generation.…”