Spatiotemporally modulated full-polarized light emission for multiplexed optical encryption

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Nature Communications volume 15, Article number: 8257 (2024 ) Cite this article reflective amplitude type

Spatiotemporal control of full freedoms of polarized light emission is crucial in multiplexed optical computing, encryption and communication. Although recent advancements have been made in active emission or passive conversion of polarized light through solution-processed nanomaterials or metasurfaces, these design paths usually encounter limitations, such as small polarization degrees, low light utilization efficiency, limited polarization states, and lack of spatiotemporal control. Here, we addressed these challenges by integrating the spatiotemporal modulation of the LED device, the precise control and efficient polarization emission through nanomaterial assembly, and the programmable patterning/positioning using 3D printing. We achieved an extremely high degree of polarization for both linearly and circularly polarized emission from ultrathin inorganic nanowires and quantum nanorods thanks to the shear-force-induced alignment effect during the protruding of printing filaments. Real-time polarization modulation covering the entire Poincaré sphere can be conveniently obtained through the programming of the on-off state of each LED pixel. Further, the output polarization states can be encoded by an ordered chiral plasmonic film. Our device provides an excellent platform for multiplexing spatiotemporal polarization information, enabling visible light communication with an exceptionally elevated level of physical layer security and multifunctional encrypted displays that can encode both 2D and 3D information.

Controlling the full degree of freedoms inherent in light in a spatiotemporal manner stands as a pivotal factor in amplifying the density of information delivered and stored1. This technological advancement exhibits significant potential for diverse applications, including parallel photonic computing2, optical encryption3, and quantum information processing and communication facilitated by single photons4. Although liquid crystalline materials are conventionally employed for switching the linear polarization of light in liquid crystal displays (LCD)5, this method incurs a 50% reduction in light source intensity due to polarizer absorption. Therefore, future devices must strive to attain effective spatiotemporal modulation of full polarized light, covering the entire Poincaré sphere of polarization without resorting to lossy polarizers6,7.

Numerous pioneering concepts have been proposed for designing metasurfaces that passively convert8 or actively emit polarization9, as well as creating nanoparticles and assemblies emitting polarized photons10,11,12,13,14,15. Notably, an aluminum plasmonic metasurface has demonstrated the reflection of six polarized light beams at different angles with distinct polarizations16. High-quality circularly polarized light (CPL) can be emitted from resonant metasurfaces by exploiting the physics of chiral quasi-bound states in the continuum9,17. However, achieving active spatiotemporal modulation of metasurfaces remains challenging and is still in its infancy1. Moreover, fabricating metasurfaces for the visible wavelength range demands sophisticated equipment and procedures18.

Polarized emission and absorption nanomaterials and assemblies offer various advantages, including low cost, scalability and substantial polarization quality19,20,21,22. Nevertheless, the integration of these materials and assemblies into contemporary fabrication technology to create functional devices for controlling polarized light remains a formidable challenge. Various design options have been proposed, such as polarized electroluminescence with organic light-emitting diodes (OLEDs)23,24, polarized light emitting diodes (LEDs) employing hybrid organic-inorganic perovskites25 or II-VI semiconductor quantum nanorods (NRs)26, as well as polarized emission resulting from incorporating fluorescent dyes into cholesterol liquid crystals27. However, these attempts are hindered by limited polarization states, low polarization degrees, low power efficiency, and a lack of spatiotemporal modulation of the polarization states, impeding the practical applications of the devices.

Here, we fabricate a six-polarized-elemental-pixels-based device by integrating the spatiotemporal modulation from LED devices, the precise polarization control through nanomaterial self-assembly, and the programmable patterning and positioning facilitated by 3D printing. Through the templated alignment of quantum NRs with ultrathin inorganic nanowires (NWs), we achieve a high degree of polarization (DOP) exceeding 0.8. The precise management of phase retardation in the printed inorganic nanowire film allows us to generate circularly polarized luminescence with an anisotropic factor (glum) reaching 1.1. By employing a linear combination of the on-off state of each pixel, we generate a multitude of polarization states. This innovative concept serves as a robust platform for multiplexing spatiotemporal information, leveraging the freedom offered by polarization. As a proof of concept, we demonstrate encryption in visible light communication (VLC), enabled by the ultralow response time and the effective polarization states modulation. To address security and intraspecificity issues in VLC, we demonstrate the achievement of exceptionally high physical layer security in optical communication via comprehensive spatiotemporal polarization modulation, leveraging chiral polarization modulators. Furthermore, we propose the concept of a multichannel display that transforms planar information into a solid figure through the novel dimension of polarization. We anticipate that this approach could significantly enhance encoding capacity, improve energy efficiency, and enable encrypted communication.

The overall design of our device draws inspiration from state-of-the-art micro-LED technology that incorporates quantum dots as the color conversion layer28,29. Micro-LED stands out as the next-generation display technology, offering advantages such as high brightness, a superior contrast ratio, rapid response time, low power consumption and extended operational life30,31. The micro-LED matrix is an ideal platform for achieving spatiotemporal modulation of polarized light emission. Our approach commences by manufacturing an individually controllable ultraviolet (UV) LED panel utilizing commercially available LED chips (Fig. 1a). For the control of linearly polarized light (LPL), corresponding to the longitude coordinates on the Poincaré sphere of polarization, quantum NRs are precisely aligned atop each UV LED pixel to convert the UV light into LPL with varying polarization orientations (Fig. 1b). CdSe@CdS NRs are selected for color conversion due to their high quantum yield, DOP, absorption section, as well as tunable spectra across visible light coupled with fast luminescence dynamics32. To generate CPL, corresponding to the latitude coordinates on the Poincaré sphere, a birefringent layer is deposited on top of the aligned NR layer to introduce the necessary phase retardation (Fig. 1b). Ultrathin inorganic NWs are selected for their polymer-like flexibility, high birefringence, transparency in the visible wavelength range, and high thermal/chemical stability33,34.

a Schematic diagram showing the overall configurations of the polarized light-controlling device. b Structure of each polarized pixel and a Poincaré sphere demonstrating the polarization control by each component of the device.

To further modulate the polarization states across the Poincaré sphere surface, a chiral plasmonic film comprising regularly-ordered chiral Au nanoparticles is constructed on top of the color conversion layer (Fig. 1b). We chose high g-factor chiral plasmonic nanoparticle, named as 432 helicoid III nanoparticles possessing their distinct circular dichroism (CD) across the visible wavelength range, developed by our group20,21. This scheme ensures polarized light emission with surprisingly high DOP/glum values along with efficient spatiotemporal modulation of multiple polarization states. The versatility of our device makes it suitable for diverse applications, including polarization-based visible light communication (VLC) and multichannel displays.

As a prototype of our polarized light controlling device, we fabricated 24 by 24 pixels with 6 distinct polarization states as a unit, including four linearly polarized pixels oriented at 0, 45, 90 and 135 degrees and two circularly polarized pixels with opposite handedness (Fig. 2a and Supplementary Fig. 2). These polarization states correspond to the points where the Cartesian axes intersect with the surface of Poincaré sphere. The printed pixels were affixed to a custom-made UV LED array, featuring 24 by 24 LED chips with individual addressability through the driving circuit. The direct ink writing (DIW) process (Fig. 2b), known for its high precision, programmability, and compatibility with nanomaterials, was employed for pixel printing35,36,37. The printing ink was formulated by blending CdSe@CdS NRs (Supplementary Fig. 3a), ultrathin NiMoO4·xH2O NWs (Supplementary Fig. 3b) and polystyrene-polyisoprene-polystyrene (SIS) polymer with toluene in specific ratios. During DIW printing, shear forces are induced due to the flow of viscous ink through the nozzle, causing the embedded one-dimensional materials to align parallel with the shear force direction. In this case, nanowires are more easily aligned with their ultra-large aspect ratios and mechanical flexibility, which act as a template to align NRs parallel with the nanowires37,38 (Fig. 2b). Microtome scanning transmission electron microscopy (STEM) and confocal microscopy images demonstrated the perfect alignment of NRs alongside NWs across nano and micro scales (Fig. 2c, Supplementary Fig. 4, and Supplementary Fig. 5).

a Photograph image of the device with 24 by 24 pixels consisting of 6 different polarization states. b Schematic diagram showing the 3D printing of one CPL pixel from CdSe@CdS NRs and NiMoO4·xH2O NWs. The zoom-in scheme shows the shear-force induced alignment of NRs and NWs during the 3D printing process. c 3D reconstruction of the microtome STEM image of the aligned NRs and NWs. d Layer number dependent phase retardation of the printed NWs film. e glum of the printed CPL films. + 45° indicates the phase retardation layer is aligned with a + 45° angle relative to the alignment direction of the luminescent layer (as shown in diagram (b)). Scale bars, 5 mm (a) and 50 nm (c).

When a linear polarizer was placed in front of the UV light-excited printed film, the observed luminescence intensity varied sinusoidally as the linear polarizer rotated (Supplementary Fig. 6a), indicating significant polarization in the emission. The DOP, evaluated using \({{\rm{DOP}}}=\frac{{I}_{\parallel -}{I}_{\perp }}{{I}_{\parallel+}{I}_{\perp }}\) , reaches up to 80% (Supplementary Fig. 6b), a value among the highest for aligned semiconductor NRs or NWs14,32,34,37,39,40,41,42 (Supplementary Table 2). Importantly, DOP values were considerably lower in the absence of NWs (Supplementary Fig. 6) due to the small aspect ratio of the quantum NRs and their poor alignment. The 3D printing technique allowed for arbitrary pattern programming and compatibility with industrial solid-state fabrication techniques, showcasing its superiority over other alignment methods. As an illustration, we printed a 10 by 10 polarization pixel array wherein each pixel measures 500 micrometers (Supplementary Fig. 7). These polarization pixels exhibited evident contrast in intensity when observed through a linear polarizer. The size of the pixel can be further reduced to below 100 micrometers using nozzles with smaller diameters, approaching the pixel size range of micro-LED displays43.

To achieve the necessary phase retardation for transforming LPL into CPL, a new birefringent ink was created consisting of ultrathin NiMoO4·xH2O NWs and SIS polymer. Microtome TEM images revealed consistent alignment of the NWs in the printing direction (Supplementary Fig. 8), a prerequisite to manifesting the collective birefringence properties of the NW assemblies. The phase retardation of the printed film was assessed using a homemade apparatus comprising a linearly polarized laser source, bandpass filters and a polarimeter (Supplementary Fig. 9). The printed films exhibited a substantial phase retardation across the visible wavelength range, increasing in proportion to the printing layer numbers (Fig. 2d). Notably, the phase retardation was negligible when NWs were absent from the ink, indicating its origin primarily from the birefringence property of the aligned NWs (Fig. 2d). Compared to other cumbersome single-crystal birefringent materials44 or inorganic nanomaterials that are aligned by magnetic field45, spinning46 or interface assembly33, our approach excels in ease of manufacture, programmability, and compatibility with industrial processes. Consequently, a quarter-wave plate based on NW was printed on top of the aligned NR/NW layer with a relative angle of ±45° using our approach. Due to the transparency of NWs in the visible wavelength range from 500 nm to 650 nm, the NW layer does not decrease the luminous intensity of the NR film significantly (Supplementary Fig. 10), maintaining high light efficiency. It should be noted, although a phase retardation is also present due to the NWs in the NR film layer, it does not affect the LPL because the optical anisotropy axis is parallel with the LPL polarization plane. The printed sample exhibited visible contrast in luminescence intensity when viewed through a pair of circular polarizers (Supplementary Fig. 11a), suggesting a high degree of circular polarization, which was confirmed by the CPL spectra measurement (Supplementary Figs. 11b–d). The glum value was calculated to reach 1.1, amongst the largest values for CPL active nanomaterials (Fig. 2e). The high DOP and glum value promise an efficient color conversion layer capable of transforming an ordinary micro-LED display panel into an effective and practical polarization controlling device alongside the validation of temporal and thermal stability (Supplementary Fig. 12 and Supplementary Fig. 13).

The emission of polarized light in our device was precisely controlled by selectively activating the UV LED chips (Fig. 3a). Subsequently, a commercial polarimeter detected the emitted polarized light, determining the full Stokes parameters of the light beam in real-time. Figure 3b illustrates the normalized Stokes parameters of the polarized component in the device’s emission. The reliability of detected polarization states extends up to a distance of 2 meters from the LED panel (Supplementary Fig. 14). It is expected that the use of a lens system will extend the fidelity of the polarization states over much greater distances, facilitating practical long-distance VLC applications47.

a Schematic diagram showing the switching-on of polarization states consisting of single polarization pixels (1 ~ 6) and the combination of different polarization states (7 ~ 12). b Normalized Stokes parameters of the polarization part for different polarization states. c SEM image of as-synthesized 432 helicoid III. Inset is an ideal model of the nanoparticle. Scale bar, 500 nm. d CD and ORD spectra of the chiral plasmonic film with assembled 432 helicoid III. 650 nm indicated with a vertical dashed line is the wavelength of interest in which polarization states were measured. e Normalized Stokes parameters of the polarization part of the output states through the chiral plasmonic film.

Remarkably, the linear combination of different polarization pixels allows for the generation of additional polarization states. For example, the simultaneous activation of LPL pixels at 0 and 45 degrees produces a linear polarization oriented at 22.5 degrees in the far field. Similarly, combinations of linear and circular pixels can result in elliptical polarization with different handedness and orientations (Fig. 3b). These polarization states are visualized on the surface of the Poincaré sphere for clarity (Supplementary Fig. 15a). The real-time modulation and detection of the multiple polarization states is stable over long-term operation (Supplementary Fig. 16 and Supplementary Movie 1). Leveraging the rapid luminescence kinetics of CdSe@CdS NRs and UV LED chips48, our device is expected to achieve polarization modulation speeds exceeding megahertz range, enabling high-bandwidth optical communication applications49. Although our current device emits red light, the straightforward incorporation of blue and green emission semiconductor NRs or NWs through printing allows us to achieve a full-color and full-polarization controlling device.

Furthermore, the polarization states can be modulated by transmission through an ordered chiral plasmonic film consisting of 432 helicoid III (Fig. 3c), which exhibits strong CD responses in the visible wavelength range (Fig. 3d and Supplementary Fig. 17)20,21. Figure 3e demonstrates the significant change in normalized Stokes parameters owing to the chiral plasmonic layer, corresponding to the evolution trajectory illustrated on the Poincaré sphere (Supplementary Figs. 15a and b). This modulation has been accurately accounted using the Muller matrix of the chiral plasmonic film derived from its CD and absorption spectra (Supplementary Figs. 15c, d and Supplementary Fig. 17). In addition, the utilization of chiral nanoparticles with opposite chirality could lead to the reversal of trajectories on the Poincaré sphere (Supplementary Fig. 18), and the expandability of polarization modulators into various chiral inorganic materials has also been demonstrated (Supplementary Fig. 19). Since the magnitude of this polarization modulation is determined by the relative effect of CD and extinction, that is, g-value, a chiral plasmonic film with a large g-value near −0.2 has superb modulation performance (Fig. 3d, e, and Supplementary Fig. 20). Further, the broadly controllable optical properties of 432 helicoid III, tailored by their shape, size, composition, and assembly structure49, are expected to enhance the security of optical communication applications.

Taking inspiration from biological systems, such as the Mantis Shrimp, which has evolved an intraspecific communication strategy using polarization-sensitive vision50, we explore the potential to introduce a new dimension in information transfer, modulation and reception through the polarization freedom enabled by our device. Thanks to the wide bandwidth, adaptability to existing environments, and inherent impermeability, VLC is recently gaining great attention as a promising avenue for 6 G wireless communication, significantly augmenting the limitations of traditional radiofrequency communication in local communication scenarios because of advantage of visible light in the directionality and high frequency51.In addition to the typical advantages of VLC such as bandwidth broadness, directivity, and robustness52, the extensive spatiotemporal polarization control and the exceptional modulation from chiral plasmonic films can provide an extremely high level of additional physical layer security. The overall VLC system diagram is depicted in Fig. 4a. To achieve maximum physical layer security, transmitters send red wavelength spectra where chiral plasmonic film has a large g-factor. Both a legitimate receiver (Bob) and a potential eavesdropper (Eve) possess photodiodes (PDs) to measure the intensity of transmitted light, while only Bob has the chiral plasmonic nanoparticle film. Wavelength division multiplexing (WDM) is employed to increase data rates by modulating multiple data streams on multiple wavelengths53. With chiral nanoparticles featuring a substantial CD, Bob can receive the transmitted symbols through two kinds of channels defined as common (S0) and differential (S3) parts, while Eve only receives the transmitted symbols via the common part of the channel (S0) (Fig. 4a and Supplementary Notes 1).

a Scheme showing the setup of the proposed polarized VLC system using our polarized light emitting device and the chiral plasmonic film consisting of 432 helicoid III nanoparticles. b Comparison of the optimized polarization symbols and the “Selected” symbols, which are obtained from simple combinations of the six polarization bases. c, d Comparison of the bit error rate (c), secrecy rate and energy efficiency (d) among the optimized polarized symbols and the selected ones when α is 0. e Comparison of the secrecy rate and energy efficiency between the optimized polarized symbols and the selected ones when α is 1. The solid line denotes the energy efficiency (left axis) and the dashed line indicates the secrecy rate (right axis) (d and e).

To mitigate errors from interference and noise, the polarization symbols are optimized by minimizing power consumption as well as maximizing the distance between symbols (Fig. 4b). We analyze the bit error rate (BER) performance and compare the secrecy rate and energy efficiency (EE) by varying α, the ratio of the common part for the symbol, ranging from 0 to 1 (Figs. 4c to e). When α is 0, the average BER of the VLC system using the optimized polarization symbols demonstrates a significantly lower BER than other schemes (Fig. 4c). The secrecy rates are improved as the transmit power (PTx) increases while the optimized symbol design shows an enhanced EE (Fig. 4d). This improvement is attributed to the strong CD of a chiral plasmonic film, enabling the receiver to obtain a differential part of the signal. Conversely, when α is 1, achieving physical layer security becomes impractical since only the common part is used to generate transmit symbols. However, the EE is significantly improved by using the common part of the channel with larger intensity compared to the differential part of the channel (Fig. 4e). Figure 4d and e verify that by balancing the common and differential parts (Fig. 4a) and thus adjusting α, it is possible to optimize polarization symbols tailored to various scenarios by balancing the secrecy rate and EE. The proposed chiral plasmonics-enabled polarized VLC system can be adopted to achieve an exceptionally elevated level of physical layer security while complementing the attenuation by chiral plasmonic film through the use of energy-efficient symbols.

The manipulation of multiple polarization states in a spatiotemporal manner enables a polarization-based multichannel encrypted display. The identification of six polarization states was accomplished by linearizing circular polarization with a quarter-waveplate (Supplementary Fig. 21a and b) and representing the azimuthal angle of linear polarization as colors through a commercial polarization camera. By rotating the waveplate, the pixel colors in the polarization camera image were algorithmically determined based on the Euclidean distance with reference colors and variance of RGB color indices. The azimuthal angle determined by the algorithm at wave plate rotation angles of 0, 45, 90, and 135 degrees were then collected and converted into the original polarization state, encompassing circular polarization (Supplementary Notes 2).

In the encrypted display, each polarization channel revealed a segment of the encrypted information, which was reconstructed by combining all the polarization channels. Encryption was implemented in both two-dimensional (2D) and three-dimensional (3D) formats. For 2D encryption, textual information was encoded and deciphered by sequentially combining messages displayed in each polarization channel (Supplementary Fig. 21c). In 3D encryption, each polarization channel displayed a single slice of the 3D object, reconstructed by volumetrically stacking the slices (Fig. 5a). As a proof-of-concept, we demonstrated the encryption of voxelized 3D structures (Fig. 5b and Supplementary Fig. 21d) using our polarized LED device and decoding system. The target chair structure was first sliced into 6 sections, presented in 6 different polarization channels. Using the polarization camera combined with a quarter-wave plate, each polarization channel was decoded to reveal the encoded images, which were then algorithmically reconstructed to display the 3D structure. The polarization information effectively served as the third dimension for the 3D display. Given the unlimited nature of polarization states, it is conceivable that higher resolution multichannel display can be achieved with more engineered polarized states and increased overall pixel numbers.

a Scheme showing the coding/readout of the multichannel display using 6 different polarization states, which were determined by a polarization camera and a rotating quarter-wave plate. Separated color scales are used for linearly and circularly polarized states. b Experimental demonstration of the multichannel display of a 3D chair. The green indicated image is a gray-scale image from the intensity channel of the polarization camera. The yellow indicated images show the polarization direction of each pixel when the quarter-wave plate is aligned at different angles. The blue indicated image is the readout result of the polarization states of each pixel represented with color scales. Finally, a 3D chair structure is reconstructed from the multi-channel display.

In this study, we developed a full-polarized light-emitting device through the integration of 3D printing of functional inorganic nanomaterials with concurrent semiconductor LED display technology. Our design strategy yielded multiple polarization states, high DOP/glum values, exceptional energy efficiency—attributes that make it an ideal solution for polarized light control. Importantly, our approach is both scalable and form-factor free, ensuring compatibility with the cutting-edge micro-LED display industry. The incorporation of chiral plasmonic assemblies introduces an additional layer of security to our device. As a result, we achieved substantial modulation of polarization states across the Poincaré sphere, rendering the system impervious to hacking attempts by external devices, and enhancing the security of VLC applications. In the realm of multichannel encrypted display, our study demonstrated the transmission of 3D information using a one-shot 2D image. This finding underscores the potential of our device in volumetric display and polarization-based holography.

Oleylamine (70%), sodium molybdate (98%), oleic acid (90%), cadmium oxide (CdO, 99.99%), hexylphosphonic acid (HPA, 95%), sulfur (99.998%), trioctylphosphine (TOP: 90%), trioctylphosphine oxide (TOPO: 90%), n-octadecylphosphonic acid (ODPA: 97%), selenium (99.99%), polystyrene-block-polyisoprene-block-polystyrene (SIS: 22 wt. % styrene content) and polystyrene (PS, average Mw~192,000), hexadecyltrimethylammonium bromide (CTAB, 99%), L-ascorbic acid (AA, 99%), Cetyltrimethylammonium chloride solution (CTAC, 25 wt. % in H2O), tetrachloroauric (III) trihydrate (HAuCl4·3H2O, 99.9%), L-glutathione (L-GSH, 98%), 1-dodecanethiol (98%), sodium borohydride (NaBH4, 99%) were purchased from Sigma-Aldrich. Nickel(II) Chloride hexahydrate (NiCl2·6H2O, 98%) was obtained from Wako chemicals. Cyclohexane (99.9%), ethanol (95%), methanol (99.8%) and toluene (99.9%) were bought from Daejung chemicals. All aqueous solutions were prepared using high-purity deionized water (18.2 MΩ cm−1).

NiMoO4·xH2O NWs were synthesized according to the literature with some modifications54. First, 30 mL of ethanol, 10 mL of oleylamine, and 5 mL of oleic acid were mixed in a 100 mL Teflon autoclave under magnetic stirring. Next, 1.5 mL of NiCl2 aqueous solution (1 M) and 1.5 mL of Na2MoO4 aqueous solution (1 M) were added dropwise into the autoclave. After stirring (800 rpm) for 10 min, the autoclave was sealed tightly and heated in an oven at 140 °C for 4 h. After finishing the reaction, the autoclave was cooled down to room temperature. After discarding the supernatant solution, the product at the bottom was dissolved in 20 mL of cyclohexane. 20 mL of ethanol was added to precipitate the product which was then collected by centrifuged at 8000 rpm for 5 min. After drying thoroughly, the precipitate was dispersed in 20 mL cyclohexane.

CdSe@CdS NRs were synthesized using a seed-mediated approach as reported previously32. For the synthesis of CdSe seeds, CdO (0.06 g), TOPO (3.0 g), and ODPA (0.280 g) were added in a 50 mL flask and heated to 150 °C and maintained for 1 h under vacuum. The solution was then heated to 300 °C to dissolve CdO under argon protection until the solution became transparent. Then, 1.8 mL of TOP was injected. The solution was heated to 370 °C and then Se:TOP solution (Se: 0.058 g; TOP: 0.360 g) was injected rapidly. After 3 minutes, the reaction vessel was cooled down to room temperature. The products were repeatedly precipitated with methanol and then dissolved with toluene to remove the by-products and unreacted reagents. After that, the products were dissolved in 4 mL of TOP. To synthesize CdSe@CdS NRs, CdO (0.086 g), TOPO (3.0 g), ODPA (0.29 g), and HPA (0.080 g) were added in a 50 mL flask and then heated to 150 °C for 1 h under vacuum. Then, under argon protection, the solution was heated to 350 °C to dissolve CdO. After injecting 1.8 g of TOP, the temperature of the solution dropped and was allowed to recover to 350 °C in several minutes. At this point, CdSe seeds and S source (200 µL of 400 µM seeds in TOP, 0.12 g S and 1.5 g TOP) were injected swiftly. After reacting for 8 minutes, the reaction solution was cooled to room temperature, and the NRs were precipitated with a mixture of toluene and methanol. At last, the NRs were dispersed in 10 mL of toluene.

Chiral Au nanoparticles were prepared using a peptide-directed, seed-mediated method20. The octahedral seed nanoparticles were obtained by growing spherical nanoparticle55,56. The brown-colored spherical nanoparticle solution was prepared by sequentially adding 8.43 mL of water, 1.32 mL of 25% w/w CTAC solution, 0.25 mL of 10 mM HAuCl4 solution, and 0.45 mL of ice-cold NaBH4 solution, and then incubating the mixture to stand at 25 °C for 1 hour. The growth solution for the octahedral nanoparticles was prepared by mixing 163 mL of water, 26.4 mL of 25% w/w CTAC solution, 5 mL of 10 mM HAuCl4 solution, 100 μL of 10 mM KI solution, and 4.4 mL of ascorbic acid solution. 40 μL of the spherical seeds were injected to a 1/20 volume of the same composition solution and mixed vigorously. If the mixture turned deep pink within 10 seconds, 0.9 mL of this mixture was added to the growth solution, followed by incubation at 30 °C for 15 minutes. The product was centrifuged twice (3515×g, 15 minutes), and the resulting nanoparticles were redispersed in a 3 mM CTAC solution. The growth solution for chiral Au nanoparticle was prepared by adding 800 μL of 100 mM CTAB, 0.2 μL of 10 mM HAuCl4, 475 μL of 100 mM AA, and 5 μL of 5 mM L-GSH (or D-GSH) to 3.95 mL of deionized water. Then, 50 μL of octahedral seed nanoparticles were injected into the growth solution and left undisturbed in a 30 °C thermostat for 2 hours. As the particles grew over time, the transparent pink solution changed into a blue color with significant scattering. Suppression of the chirality evolution of nanoparticles was achieved by reducing HAuCl4 and L-GSH to half in concentration (Supplementary Fig. 20). The solution was centrifuged twice (2000×g, 3 minutes) to remove unreacted reagents and then redispersed in 1 mM CTAB.

The as-synthesized Au nanoparticles were periodically incorporated into a 400-nm-pitch square nanowell array on PDMS (21). The nanopatterned PDMS was prepared by sequentially spin-coating and thermally curing h-PDMS and 184-PDMS on a silicon nanopillar master substrate and carefully peeling it off. Au nanoparticles were assembled through water-organic interfacial assembly; 5 mL of absolute ethanol was gradually injected into the interface of stratified n-hexane (2 mL) and Au nanoparticles (1 mL) in a Teflon cell. A dense monolayer assembly of nanoparticles was obtained by removing the top n-hexane layer and was immediately transferred onto the PDMS nanopattern. Transferred nanoparticles were mechanically inserted into the nano-wells by rubbing the surface with a 1-Dodecanethiol-decorated Teflon stick.

The luminescent ink was prepared by adding 2 ~ 20 mg CdSe@CdS NRs and/or 0 ~ 100 mg NiMoO4·xH2O NWs into 3 mL of toluene. After brief sonication ( ~ 5 min), 2.0 g SIS or PS was added into the nanomaterial solution. Magnetic stirring (100 rpm) was used to facilitate the dissolving of polymers and the dispersion of nanomaterials in the polymer solutions. The transparent nanowire composite ink was prepared by adding 250 mg of NiMoO4·xH2O NWs into 3 mL of toluene. The other procedures are the same as that of the luminescent ink.

Direct ink writing was conducted using a 3DX printer from T&R Biofab. G-code was generated using T&R CAM software. The ink was loaded into a 10 mL luer-lock polypropylene syringe. Precision nozzles with an inner diameter of 0.10 mm (Iwashita Engineering) were used for the printing of polarized LED devices. The printing speed is maintained at 200 mm/min while the pressure was set at 400 kPa. The pitch distance between two adjacent printing filaments was set to be 0.1 mm.

The 24 by 24 UV LED device operated under constant current. UV LED chips (CUN6LF1C) are purchased from Seoul Viosys company with the luminescence centered around 365 nm, and FWHM bandwidth of 10 nm. A total of 576 UV-LEDs were equally spaced apart, arranged 24 by 24, and loaded onto a customized PCB to supply with the same current. The operation voltage was 3.3 V, and the forward current was 10 mA. To minimize interference between adjacent LEDs, the gaps between the LED cells were covered with 3D-printed barriers. To make the polarized LED device, we first print 24 by 24 polarized pixels on top of an ultrathin glass (Eagle-XG glass, Corning) with a thickness of 0.3 mm. Each pixel measures 3.5×3.5 mm2. Each 6 pixels form a unit, which contains 4 linear polarizations along 0, 45, 90 and 135 degrees and two opposite circular polarizations. For linear polarization pixels, 4 layers of aligned NW/NR films were printed with an interlayer distance of 30 μm. For the circular polarization pixels, 4 layers of birefringent NW films were printed on top of the linear polarization pixels, with an interlayer distance of 30 μm. Then, the printed pixels on the ultrathin glass were attached onto the LED device in alignment with the UV LED chips. Each pixel of the polarized light devices was controlled by a microcontroller unit (MCU). All LED programming was based on the C + + language.

Phase retardation of the printed NW composites was measured using a homemade optical setup. A white light laser sequentially transmitted through a neutral density filter, a linear polarizer and a band-pass filter to become horizontally polarized light centered around a specific visible wavelength (Eq. S1). After transmitting through the printed birefringent film which was aligned at 45°, the incident light was transformed into elliptical polarized light. A polarimeter (PAX1000VIS, Thorlabs) was used to detect the full Stokes parameter of the output polarized light. According to the Muller calculus, the output light is related to the incident light by:

where \(\varphi\) is the phase retardation of the birefringent film.

CD and extinction spectra of the 432-helicoid Au nanoparticles were measured with a J-1700 spectropolarimeter (JACSO). CPL spectra were measured with a CPL-300 spectrometer (JASCO) at room temperature. The glum factor was calculated as:

where DC denotes the total photoluminescence intensity. Fluorescence spectra of as-synthesized quantum NRs were measured with a FluoTime 300 spectrometer (PicoQuant). The degree of polarization (DOP) of the printed NRs/NWs polymer film was measured by inserting a linear polarizer before the detector of the photoluminescence spectrometer. The polarizer was rotated at different angles with an interval of 15°. The photoluminescence intensity was fitted with a cosine2 function to obtain the intensity polarized along (\({I}_{\parallel }\) ) and vertical (\({I}_{\perp }\) ) to the NR alignment direction. The DOP was derived as:

Polarization images were taken with a commercial polarization camera (SVS-VISTEK) featuring a polarized megapixel sensor (Sony PolarSens technology). Polarization states of the emission from the polarized LED panel were detected in real-time with a polarimeter (PAX1000VIS, thorlabs).

The printed NRs/NWs PS film was sliced into thin sections with a thickness of 60 nm using an ultramicrotome (EM-UC7, Leica). The sections supported onto a TEM grid were mounted on a single-tilt tomography holder. The series of TEM images were acquired with the tilt angle from −26° to +22° by an increment of 2° using a Cs corrected (S)TEM (Themis Z, Thermo Fisher). The alignment and the reconstruction to 3D images were performed using Inspect3D software (Thermo Fisher). Subsequently, 3D rendering and segmentation were conducted with Avizo software (Thermo Fisher). STEM images and energy dispersive spectrometry (EDS) mapping were acquired using the same (S)TEM instrument. TEM images of the as-synthesized quantum NRs and NWs were obtained using a JEM-2100F (JEOL).

The data that support this study are available within the manuscript and the supplementary information. Source data are provided with this paper.

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This research was supported by the Challengeable Future Defense Technology Research and Development Program (912909601) of Agency for Defense Development in 2022, the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2021R1A4A5031762), LG Display under the LGD-SNU Incubation Program, and Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (2021-0-00847). K.T.N. appreciates the administrative and technical support from Institute of Engineering Research, Research Institute of Advanced Materials (RIAM), and SOFT foundry institute.

These authors contributed equally: Jiawei Lv, Jeong Hyun Han, Geonho Han.

Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea

Jiawei Lv, Jeong Hyun Han, Seung Ju Kim, Ryeong Myeong Kim, Jung‐El Ryu, Rena Oh, In Han Ha, Yoon Ho Lee, Gyeong‐Su Park, Ho Won Jang, Junsang Doh & Ki Tae Nam

School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea

Geonho Han, Hyuckjin Choi, Minje Kim & Junil Choi

Interdisciplinary Program in Bioengineering, Seoul National University, Seoul, Republic of Korea

Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea

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K.T.N. and J.C. conceived and supervised this work. The synthesis and optical characterization of materials were conducted by J.L., J.H.H., R.M.K., I.H.H., and Y.H.L. under the supervision of K.T.N. Direct ink writing of materials was performed by J.L., S.A., J.D. Fabrication and control of the LED backplane were realized by S.J.K., J-E.R., H.W.J. The VLC algorithm was designed and modeled by G.H., H.C., M.K. under the supervision of J.C. Microstructural characterization using (S)TEM was conducted by J.L., J.H.H., R.O., G-S.P. Demonstration of multichannel display was carried out by J.L. and J.H.H. All authors discussed the results and commented on the manuscript. K.T.N. guided all aspects of the work.

Correspondence to Junil Choi or Ki Tae Nam.

The authors declare no competing interests.

Nature Communications thanks the anonymous, reviewers for their contribution to the peer review of this work. A peer review file is available.

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Lv, J., Han, J.H., Han, G. et al. Spatiotemporally modulated full-polarized light emission for multiplexed optical encryption. Nat Commun 15, 8257 (2024). https://doi.org/10.1038/s41467-024-52358-7

DOI: https://doi.org/10.1038/s41467-024-52358-7

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Spatiotemporally modulated full-polarized light emission for multiplexed optical encryption | Nature Communications