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Silicon is the dominant material in complementary metal-oxide-semiconductor (CMOS) imaging devices because of its outstanding electrical and optical properties, well-established fabrication methods, and abundance in nature. However, with the ongoing trend toward electronic miniaturization, which demands smaller pixel sizes in CMOS image sensors, issues, such as crosstalk and reduced optical efficiency, have become critical. These problems stem from the intrinsic properties of Si, particularly its low absorption in the long wavelength range of the visible spectrum, which makes it difficult to devise effective solutions unless the material itself is changed. Recent advances in optical metasurfaces have offered new possibilities for solving these problems. In this study, we propose color arrestor pixels (CAPs) as a new class of color image sensors whose composite spectral responses directly mimic those of the human eye. The key idea is to employ linearly independent combinations of standardized color matching functions. These new basis functions allow our device to reproduce colors more accurately than the currently available image sensors with red-green-blue filters or other metasurface-based sensors, demonstrating an average CIEDE2000 color difference value of only 1.79 when evaluating 24 colors from the Gretag-Macbeth chart under standard illuminant D65. Owing to their high fidelity to the human eye response, CAPs consistently exhibit exceptional color reproduction accuracy under various spectral illumination compositions. With a small footprint of 860 nm height and 221 nm full-color pixel pitch, the CAPs demonstrated high absorption efficiencies of 79 %, 81 %, and 63 % at wavelengths of 452 nm, 544 nm, and 603 nm, respectively, and good angular tolerance. With such a high density of pixels efficiently capturing accurate colors, CAPs present a new direction for optical image sensor research and their applications.

Proximity-field nanopatterning (PnP) have been used recently as a rapid, cost-effective, and large-scale fabrication method utilizing volumetric interference patterns generated by conformal phase masks. Despite the effectiveness of PnP processes, their design diversity has not been thoroughly explored. Here, we demonstrate that the possibility of generating any two-dimensional lattice with diverse motifs. By controlling the amplitude, phase, and polarization of each diffraction beam, we can implement all two-dimensional Bravais lattices in three-dimensional space. The results may provide diverse applications that require three-dimensional nanostructures from optical materials and structural materials to energy storage or conversion materials.

Hiding terrestrial objects from aerial monitoring has long been an important objective in national security and public safety. However, the diversity of terrestrial environments raises great challenges to traditional camouflages optimized for a single spectral band or single type of background environment, rendering them vulnerable in other bands or backgrounds. Herein, we experimentally demonstrate simultaneous visual and thermal camouflage that can adapt to two different environments based on a thermally emissive electrochromic layer. We first explore diverse possible theoretical solutions for dual-band dual-environmental camouflage by solving analytic constraints for camouflage and steady-state thermal conditions and select the most viable approach. Based on the theoretical analysis, we design active camouflage thin-film material systems that can approximate two different target visible and infrared signatures of backgrounds under proper bias voltage. Our potentially flexible camouflage surfaces can also conceal heat sources such as human body as well with tailored designs. These results provide new directions in multi-band stealth designs.

Optical metasurfaces have great potential to overcome the functional limitations of conventional optical devices. In addition to polarization- or wavelength-multiplexed metasurfaces, angle-multiplexed metasurfaces can provide new degrees of freedom, enabling previously unrealized complex functionality in diverse applications such as LiDAR, augmented reality glasses, and imaging. However, there have been fundamental trade-offs in transmission efficiency and angular sensitivity for practically important paraxial rays. In this paper, we overcome this limitation by breaking mirror symmetries of single-layer metasurface structures. Based on an effective medium theory, we intuitively explain which material parameters affect the sensitivity and efficiency and prove that high sensitivity and high efficiency can be achieved simultaneously by breaking the mirror symmetry. Based on this, we propose optimized metasurfaces for two applications: an angle-multiplexed beam-steering device with up to 93% relative efficiency and an angle-multiplexed metalens array that can break the fundamental resolution–density trade-off of microlens arrays with high efficiency. The proposed angle-selective designs could pave the way for the development of new classes of compact optical devices with novel functions.

Metalenses have potential to replace various bulky conventional optical elements with ultrathin nanostructure arrays. In particular, active metalenses with reconfigurable focusing capability have attracted considerable interest from the academic and industrial communities. However, their tuning range is currently restricted by limited material properties and fabrication difficulties. Here, a hybrid optical system capable of three-dimensional relocation of a focal spot is proposed and experimentally demonstrated. The system comprises a mechanically actuated passive metalens doublet that can be easily fabricated with commonly available materials and processes. An incident laser can be focused to a desired point in three-dimensional space simply by rotating two metalenses or changing their separation. In addition, exploiting the polarization-multiplexing capability of metasurfaces, a hologram is incorporated to the metalenses to guide rotational and positional alignment of two metasurfaces. The ease of fabrication and alignment provided by this approach could widen its application to many practical fields.

Iterative numerical optimization is a ubiquitous tool to design optical nanostructures. However, there can be a significant performance gap between the numerically simulated results, with pristine shapes, and the experimentally measured values, with deformed profiles. We introduce conditional generative adversarial networks (CGAN) into the standard iterative optimization loop to learn process-structure relationships and produce realistic simulation designs based on the fabrication conditions. This ensures that the process-structure mapping is accurate for the specific available equipment and moves the optimization space from the structural parameters (e.g. width, height, and period) to process parameters (e.g. deposition rate and annealing time). We demonstrate this model agnostic optimization platform on the design of a red, green, and blue color filter based on metallic gratings. The generative network can learn complex M-to-N nonlinear process-structure relations, thereby generating simulation profiles similar to the training data over a wide range of fabrication conditions. The CGAN-based optimization resulted in fabrication parameters leading to a realistic design with a higher figure of merit than a standard optimization using pristine structures. This data-driven approach can expedite the design process both by limiting the design search space to a fabrication-accurate subspace and by returning the optimal process parameters automatically upon obtaining the optimal structure design.

The intrinsic geometry of wavevector diagrams describes electronic or photonic transport at a given energy level. Lifshitz transition is an intriguing example of the topological transition in wavevector diagrams, which plays a critical role in abnormal transport with enhanced magnetoresistance or superconductivity. Here, we develop the spatial analogy of the Lifshitz transition, which provides a comprehensive topological perspective on transverse-spin interface states. We establish the excitation conditions of transverse-spin interface states, which require the “Lifshitz interface” – the interface between different topologies of wavevector diagrams – along with the gap in wavevector diagrams. Based on the detailed analysis of this topological phenomenon with respect to the dimensionality and gaps of wavevector diagrams across the Lifshitz interface, we show distinct parity of transverse spins and power flows in transverse-spin modes. The unique symmetry of interface states realizing Abraham-spin-momentum locking represents the gauge induced by the Lifshitz interface, which provides a novel insight into the Abraham–Minkowski controversy.

Smart chromatic materials with optical transmittances that can be modified by light scattering upon external stimuli are attracting extensive interest because of their appealing applications in smart windows, privacy protection, electronic displays, etc. However, the development of these scatterers, which are mostly activated by electric fields, is hindered by their intrinsic energy consumption, slow responses, and poor stability. Recently, mechanoresponsive scatterers based on a strain-driven reconfiguration of the surface or internal structure have emerged, featuring fast responses and a simple composition/fabrication. Because there is no energy consumption to maintain the transparency/opacity, this novel scheme for scatterers holds great promise to break the existing bottleneck. This article presents recent advances in the development of mechanoresponsive scatterers and compares different structural design strategies. The scatterers are categorized into 2D, 3D, and other types according to the dimensions of their functioning structures. The fabrication methods, mechanisms, and relationships between the structural parameters and optical modulating performances are discussed for each category. Next, the potential applications of these scatterers are outlined. Finally, the advantages and disadvantages of the mainstream 2D and 3D categories are summarized, followed by a perspective on future research directions.

Metamaterials can possess extraordinary properties not readily available in nature. While most of the early metamaterials had narrow frequency bandwidth of operation, many recent works have focused on how to implement exotic properties and functions over broad bandwidth for practical applications. Here, we provide two definitions of broadband operation in terms of effective material properties and device functionality, suitable for describing materials and devices, respectively, and overview existing broadband metamaterial designs in such two categories. Broadband metamaterials with nearly constant effective material properties are discussed in the materials part, and broadband absorbers, lens, and hologram devices based on metamaterials and metasurfaces are discussed in the devices part.

The quantum plasmonics field has emerged and been growing increasingly, including study of single emitter-light coupling using plasmonic system and scalable quantum plasmonic circuit. This offers opportunity for the quantum control of light with compact device footprint. However, coupling of a single emitter to highly localized plasmonic mode with nanoscale precision remains an important challenge. Today, the spatial overlap between metallic structure and single emitter mostly relies either on chance or on advanced nanopositioning control. Here, we demonstrate deterministic coupling between three-dimensionally nanofocused plasmonic modes and single quantum dots (QDs) without any positioning for single QDs. By depositing a thin silver layer on a site-controlled pyramid QD wafer, three-dimensional plasmonic nanofocusing on each QD at the pyramid apex is geometrically achieved through the silver-coated pyramid facets. Enhancement of the QD spontaneous emission rate as high as 22 ± 16 is measured for all processed QDs emitting over ∼150-meV spectral range. This approach could apply to high fabrication yield on-chip devices for wide application fields, e.g., high-efficiency light-emitting devices and quantum information processing.

Terrestrial radiative cooling is an intriguing way to mitigate the accelerating cooling demands in the residential and commercial sectors by offering zero‐energy cooling. However, the ultra‐white or mirror‐like appearance of radiative coolers can be visually sterile and raise safety issues when applied to building facades and vehicles en masse. To overcome the fundamental trade‐off between color diversity and cooling performance, a radiatively integrated, conductively insulated material system is proposed that exploits thermal non‐equilibrium between colorants and thermal emitters. This allows such radiative coolers to be cooled below the ambient temperature at all times of the day while exhibiting any desired exterior color including black without using vacuum insulation. This work experimentally demonstrates that even black coolers, absorbing 646 W m−2 of solar power under AM1.5 conditions, cool down to a maximum of 6.9 K (average of 3.5 K) below the ambient temperature during the daytime. These systems can potentially be used in outdoor applications, especially in commercial buildings and residential houses, where carbon‐free thermal management is in high demand but diversity of colors is also important for visual appeal and comfort. [ABSTRACT FROM AUTHOR]

This paper describes a new approach, based on the Mie theory, to measure the dielectric properties of lossless materials at temperatures greater than 1500 °C. For the reliable operation of microwave transmitting materials in harsh environments, it is crucial to correctly characterize the permittivity under various temperature conditions. Heating and measurement systems using a propane torch and a single horn antenna were designed to estimate such dielectric properties. The reflection spectrum of Al2O3 ceramics at room temperature was determined using the Mie theory to derive the permittivity and validate the approach. High-temperature dielectric constants are derived from simulated values, which are reliable and have only a slight slope as a function of temperature. These results indicate that the permittivity measurement technique can provide powerful information for the optimal design and accurate evaluation of the dielectric properties of various lossless materials at high temperatures. [ABSTRACT FROM AUTHOR]