Creating the ultimate virtual reality display

Simple Boron-Nitrogen Covalent Bond Constructs Multi-Resonance TADF Emitters: Ultra-Narrowband Deep-Blue Electroluminescence

High-efficiency, pure deep-blue emitters are critically needed to meet the rising demands of ultra-high-definition displays. Although high-order B/N-doped polycyclic aromatic hydrocarbons (PAHs) leveraging multi-resonance (MR) effects show promise, their complex syntheses and large molecular weights hinder practical application. Here, we report a compact MR framework featuring three nitrogen-linked boron centers, synthesized at the gram scale via a single-step, amine-directed borylation. This emitter displays deep-blue emission with an ultra-narrow full-width at half-maximum (FWHM) of 13 nm and achieves an order-of-magnitude increase in the reverse intersystem crossing rate constant (kRISC) compared to previous BN-bond-based blue MR emitters. Theoretical studies reveal that its π-extended framework and partially distorted geometry synergistically minimize structural relaxation to reduce FWHM and enhance spin-orbit coupling to facilitate efficient spin-flip processes. As a result, the corresponding deep-blue organic light-emitting diodes exhibit an FWHM of 15 nm and a high maximum external quantum efficiency (ηEQE,max) approaching 30% at color coordinates of (0.155, 0.060), rivaling the leading performance of deep-blue OLEDs based on conventional B/N-doped frameworks.

Highly Efficient, Tunable, Electro-Optic, Reflective Metasurfaces Based on Quasi-Bound States in the Continuum

Ultrafast and highly efficient dynamic optical metasurfaces enabling truly spatiotemporal control over optical radiation are poised to revolutionize modern optics and photonics, but their practical realization remains elusive. In this work, we demonstrate highly efficient electro-optical metasurfaces based on quasi-bound states in the continuum (qBIC) operating in reflection that are amenable for ultrafast operation and thereby spatiotemporal control over reflected optical fields. The material configuration consists of a lithium niobate thin film sandwiched between an optically thick gold back-reflector and a grating of gold nanoridges also functioning as control electrodes. Metasurfaces for optical free-space intensity modulation are designed by utilizing the electro-optic Pockels effect in combination with an ultranarrow qBIC resonance, whose wavelength can be finely tuned by varying the angle of light incidence. The fabricated electro-optic metasurfaces operate at telecom wavelengths, with the modulation depth reaching 95% (modulating thereby 35% of the total incident power) for a bias voltage of ±30 V within the electrical bandwidth of 125 MHz. Leveraging the highly angle-dependent qBIC resonance realized, we demonstrate electrically tunable phase-contrast imaging by using the fabricated metasurface. Moreover, given the potential bandwidth of 39 GHz estimated for the metasurface pixel size of 22 μm, the demonstrated electro-optic metasurfaces promise successful realization of unique optical functions, such as harmonic beam steering and spatiotemporal shaping as well as nonreciprocal operation.

MolecularWebXR: Multiuser discussions in chemistry and biology through immersive and inclusive augmented and virtual reality

MolecularWebXR is a new web-based platform for education, science communication and scientific peer discussion in chemistry and biology, based on modern web-based Virtual Reality (VR) and Augmented Reality (AR). With no installs as it is all web-served, MolecularWebXR enables multiple users to simultaneously explore, communicate and discuss concepts about chemistry and biology in immersive 3D environments, by manipulating and passing around objects with their bare hands and pointing at different elements with natural hand gestures. Users may either be present in the same physical space or distributed around the world, in the latter case talking naturally with each other thanks to built-in audio. While MolecularWebXR offers the most immersive experience on high-end AR/VR headsets, its WebXR core also supports participation on consumer devices such as smartphones (with optional cardboard goggles for enhanced immersion), computers, and tablets. MolecularWebXR includes preset VR rooms covering topics in general, inorganic, and organic chemistry, as well as biophysics, structural biology, and general biology. Users can also add new content via the PDB2AR tool. We demonstrate MolecularWebXR's versatility and ease of use across a wide age range (12-80) in fully virtual and mixed real-virtual sessions at science outreach events, undergraduate and graduate courses, scientific collaborations, and conference presentations. MolecularWebXR is available for free use without registration at https://molecularwebxr.org. A blog post version of this preprint with embedded videos is available at https://go.epfl.ch/molecularwebxr-blog-post.

Electrochemically mutable soft metasurfaces

Active optical metasurfaces, capable of dynamically manipulating light in ultrathin form factors, enable novel interfaces between humans and technology. In such interfaces, soft materials bring many advantages based on their flexibility, compliance and large stimulus-driven responses. Here, we create electrochemically mutable, soft metasurfaces that capitalize on the swelling of soft conducting polymers to alter the shape and associated resonant response of metasurface elements. Such geometric tuning overcomes the typical trade-off between achieving substantial tuning and low optical loss that is intrinsic to dynamic metasurfaces relying on index tuning of materials. Using the commercial polymer PEDOT:PSS, we demonstrate dynamic, high-resolution colour tuning and high-diffraction-efficiency (>19%) beam-steering devices that operate at CMOS-compatible voltages (~1.5 V). These results highlight how the deformability of soft materials can enable a class of high-performance metasurfaces that are suitable for body-worn technologies.

Continuously focus tunable 2D/3D switchable cylindrical liquid crystal microlens arrays for autostereoscopic displays

Cylindrical microlens arrays are important optical elements for autostereoscopic display. Conventional fixed focal length cylindrical microlens arrays do not allow switching between 2D mode and 3D mode when constructing a 3D viewing zone. In contrast, cylindrical liquid crystal microlens arrays with zoom characteristics allow switching between 2D and 3D states, as well as adjusting the width of the sub-viewing zone. Therefore, based on the quantitative analysis of the geometrical structure of the viewing zone in different states, this paper proposes a continuous zoom type cylindrical liquid crystal microlens array structure, which is a liquid crystal cell composed of an array of plano-concave glass substrates and planar glass substrates. Theory and experiments show that it is close to a favorable parabolic phase profile at different driving voltages, and at the same time, it can realize a zoom range of 1.6mm-36 mm at a smaller driving voltage. The wide zoom range and excellent zoom effect make this structure particularly suitable for autostereoscopic display, and this characteristic can achieve the effect of switching between 2D and 3D by adjusting the shape of the central viewing zone.

Multi-Color Spaceplates in the Visible

The ultimate miniaturization of any optical system relies on the reduction or removal of free-space gaps between optical elements. Recently, nonlocal flat optic components named "spaceplates" were introduced to effectively compress space for light propagation. However, space compression over the visible spectrum remains beyond the reach of current spaceplate designs due to their inherently limited operating bandwidth and functional inefficiencies in the visible range. Here, we introduce "multi-color" spaceplates performing achromatic space compression at three distinct color channels across the visible spectrum to markedly miniaturize color imaging systems. In this approach, we first design monochromatic spaceplates with high compression factors and high transmission amplitudes at visible wavelengths based on a scalable structure and dielectric materials widely used in the fabrication of meta-optical components. We then show that the dispersion-engineered combination of monochromatic spaceplates with suitably designed transmission responses forms multicolor spaceplates that function achromatically. The proposed multicolor spaceplates, composed of amorphous titanium dioxide and silicon dioxide layers, efficiently replace free-space volumes with compression ratios as high as 4.6, beyond what would be achievable by a continuously broadband spaceplate made of the same materials. Our strategy for designing monochromatic and multicolor spaceplates, along with the presented theoretical and computational results, show that strong space-compression effects can be achieved in the visible range. Our findings may ultimately enable a new generation of ultrathin optical devices for various applications.

Reconfigurable Micro/Nano-Optical Devices Based on Phase Transitions: From Materials, Mechanisms to Applications

In recent years, numerous efforts have been devoted to exploring innovative micro/nano-optical devices (MNODs) with reconfigurable functionality, which is highly significant because of the progressively increasing requirements for next-generation photonic systems. Fortunately, phase change materials (PCMs) provide an extremely competitive pathway to achieve this goal. The phase transitions induce significant changes to materials in optical, electrical properties or shapes, triggering great research interests in applying PCMs to reconfigurable micro/nano-optical devices (RMNODs). More specifically, the PCMs-based RMNODs can interact with incident light in on-demand or adaptive manners and thus realize unique functions. In this review, RMNODs based on phase transitions are systematically summarized and comprehensively overviewed from materials, phase change mechanisms to applications. The reconfigurable optical devices consisting of three kinds of typical PCMs are emphatically introduced, including chalcogenides, transition metal oxides, and shape memory alloys, highlighting the reversible state switch and dramatic contrast of optical responses along with designated utilities generated by phase transition. Finally, a comprehensive summary of the whole content is given, discussing the challenge and outlooking the potential development of the PCMs-based RMNODs in the future.

Full-colour 3D holographic augmented-reality displays with metasurface waveguides

Emerging spatial computing systems seamlessly superimpose digital information on the physical environment observed by a user, enabling transformative experiences across various domains, such as entertainment, education, communication and training1-3. However, the widespread adoption of augmented-reality (AR) displays has been limited due to the bulky projection optics of their light engines and their inability to accurately portray three-dimensional (3D) depth cues for virtual content, among other factors4,5. Here we introduce a holographic AR system that overcomes these challenges using a unique combination of inverse-designed full-colour metasurface gratings, a compact dispersion-compensating waveguide geometry and artificial-intelligence-driven holography algorithms. These elements are co-designed to eliminate the need for bulky collimation optics between the spatial light modulator and the waveguide and to present vibrant, full-colour, 3D AR content in a compact device form factor. To deliver unprecedented visual quality with our prototype, we develop an innovative image formation model that combines a physically accurate waveguide model with learned components that are automatically calibrated using camera feedback. Our unique co-design of a nanophotonic metasurface waveguide and artificial-intelligence-driven holographic algorithms represents a significant advancement in creating visually compelling 3D AR experiences in a compact wearable device.

Photo-Modulated Ionic Polymer as an Adaptable Electron Transport Material for Optically Switchable Pixel-Free Displays

In addition to electrically driven organic light-emitting diode (OLED) displays that rely on complicated and costly circuits for switching individual pixel illumination, developing a facile approach that structures pixel-free light-emitting displays with exceptional precision and spatial resolution via external photo-modulation holds significant importance for advancing consumer electronics. Here, optically switchable organic light-emitting pixel-free displays (OSPFDs) are presented and fabricated by judiciously combining an adaptive photosensitive ionic polymer as electron transport materials (ETM) with external photo-modulation as the switching mode while ensuring superior illumination performance and seamless imaging capability. By irradiating the solution-processed OSPFDs with light at specific wavelengths, efficient and reversible tuning of both electron transport and electroluminescence is achieved simultaneously. This remarkable control is achieved by altering the energetic matching within OSPFDs, which also exhibits a high level of universality and adjustable flexibility in the three primary color-based light-emitting displays. Moreover, the ease of creating and erasing desired pixel-free emitting patterns through a non-invasive photopatterning process within a single OSPFD is demonstrated, thereby rendering this approach promising for commercial displaying devices and highly precise pixelated illuminants.

Carrier Transport Regulation of Pixel Graphene Transparent Electrodes for Active-Matrix Organic Light-Emitting Diode Display

Integrating a graphene transparent electrode (TE) matrix with driving circuits is essential for the practical use of graphene in optoelectronics such as active-matrix organic light-emitting diode (OLED) display, however it is disabled by the transport of carriers between graphene pixels after deposition of a semiconductor functional layer caused by the atomic thickness of graphene. Here, the carrier transport regulation of a graphene TE matrix by using an insulating polyethyleneimine (PEIE) layer is reported. The PEIE forms an ultrathin uniform film (≤10 nm) to fill the gap of the graphene matrix, blocking horizontal electron transport between graphene pixels. Meanwhile, it can reduce the work function of graphene, improving the vertical electron injection through electron tunneling. This enables the fabrication of inverted OLED pixels with record high current and power efficiencies of 90.7 cd A-1 and 89.1 lm W-1 , respectively. By integrating these inverted OLED pixels with a carbon nanotube-based thin-film transistor (CNT-TFT)-driven circuit, an inch-size flexible active-matrix OLED display is demonstrated, in which all OLED pixels are independently controlled by CNT-TFTs. This research paves a way for the application of graphene-like atomically thin TE pixels in flexible optoelectronics such as displays, smart wearables, and free-form surface lighting.

Integrated metasurfaces for re-envisioning a near-future disruptive optical platform

Metasurfaces have been continuously garnering attention in both scientific and industrial fields, owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. To date, research has mainly focused on the full control of electromagnetic characteristics, including polarization, phase, amplitude, and even frequencies. Consequently, versatile possibilities of electromagnetic wave control have been achieved, yielding practical optical components such as metalenses, beam-steerers, metaholograms, and sensors. Current research is now focused on integrating the aforementioned metasurfaces with other standard optical components (e.g., light-emitting diodes, charged-coupled devices, micro-electro-mechanical systems, liquid crystals, heaters, refractive optical elements, planar waveguides, optical fibers, etc.) for commercialization with miniaturization trends of optical devices. Herein, this review describes and classifies metasurface-integrated optical components, and subsequently discusses their promising applications with metasurface-integrated optical platforms including those of augmented/virtual reality, light detection and ranging, and sensors. In conclusion, this review presents several challenges and prospects that are prevalent in the field in order to accelerate the commercialization of metasurfaces-integrated optical platforms.

Large-scale optical compression of free-space using an experimental three-lens spaceplate

Recently introduced, spaceplates achieve the propagation of light for a distance greater than their thickness. In this way, they compress optical space, reducing the required distance between optical elements in an imaging system. Here we introduce a spaceplate based on conventional optics in a 4-f arrangement, mimicking the transfer function of free-space in a thinner system - we term this device a three-lens spaceplate. It is broadband, polarization-independent, and can be used for meter-scale space compression. We experimentally measure compression ratios up to 15.6, replacing up to 4.4 meters of free-space, three orders of magnitude greater than current optical spaceplates. We demonstrate that three-lens spaceplates reduce the length of a full-color imaging system, albeit with reductions in resolution and contrast. We present theoretical limits on the numerical aperture and the compression ratio. Our design presents a simple, accessible, cost-effective method for optically compressing large amounts of space.