Optical neural networks (ONNs) are emerging as a promising neuromorphic computing paradigm for object recognition, offering unprecedented advantages in light-speed computation, ultra-low power consumption, and inherent parallelism. However, most of ONNs are only capable of performing simple object classification tasks. These tasks are typically constrained to single-object scenarios, which limits their practical applications in multi-object recognition tasks. Here, we propose an anti-interference diffractive deep neural network (AI D2NN) that can accurately and robustly recognize targets in multi-object scenarios, including intra-class, inter-class, and dynamic interference. By employing different deep-learning-based training strategies for targets and interference, two transmissive diffractive layers form a physical network that maps the spatial information of targets all-optically into the power spectrum of the output light, while dispersing all interference as background noise. We demonstrate the effectiveness of this framework in classifying unknown handwritten digits under dynamic scenarios involving 40 categories of interference, achieving a simulated blind testing accuracy of 87.4% using terahertz waves. The presented framework can be physically scaled to operate at any electromagnetic wavelength by simply scaling the diffractive features in proportion to the wavelength range of interest. This work can greatly advance the practical application of ONNs in target recognition and pave the way for the development of real-time, high-throughput, low-power all-optical computing systems, which are expected to be applied to autonomous driving perception, precision medical diagnosis, and intelligent security monitoring.

Investigating chiral light-matter interactions is essential for advancing applications in sensing, imaging, and pharmaceutical development.

Thermoelectric materials can be designed to support optical resonances across multiple spectral ranges to enable ultra-wide band photodetection. For instance, antimony telluride (Sb2Te3) chalcogenide exhibits interband plasmonic resonances in the visible range and Mie resonances in the mid-infrared (mid-IR) range, while simultaneously possessing large thermoelectric Seebeck coefficients. In this paper, we designed and fabricated Sb2Te3 metasurface devices to achieve resonant absorption for enabling photodetectors operating across an ultra-wideband spectrum, from visible to mid-IR. Furthermore, relying on asymmetric Sb2Te3 metasurface, we demonstrated the thermoelectric photodetectors with polarization-selectivity. This work provides a potential platform towards the portable ultrawide band spectrometers at room temperature, for environmental sensing applications.

Weyl semimetals have attracted significant interest in condensed matter physics and materials science, due to their unique electronic and topological properties. These characteristics not only deepen the understanding of fundamental quantum phenomena, but also make Weyl semimetals promising candidates for advanced applications in electronics, photonics, and spintronics. This review provides a systematic overview of the field, covering theoretical foundations, material synthesis, engineering strategies, and emerging device applications. This study first outlines the key theoretical principles and distinctive properties of Weyl semimetals, followed by an examination of recent advancements that enhance their functional versatility. Finally, this study discusses the critical challenges hindering their practical implementation and explore future development directions, along with the potential for expanding and enhancing their existing range of applications. By integrating discussions of both opportunities and obstacles, this review offers a balanced perspective on current progress and future directions in Weyl semimetal research.

Sb2Te3 and Ge2Sb2Te5 (GST) are important materials used in phase-change photonic devices. We investigated the tunable optical properties of Sb2Te3, demonstrating its potential for continuous tuning from metallic-like to dielectric behavior through intermediate amorphous states. Using a resonant thin-film structure, we explored how Sb2Te3 may enable continuous color modification. We have also designed and simulated optical reflectors to enhance color tuning by gradually disordering the Sb2Te3 crystal structure. These results suggest that gradual changes in the optical properties of Sb2Te3 could be potentially used for future visible photonic applications, such as zero-static power tunable color reflective displays.

Inkjet printing emerges as a versatile on-demand patterning technique for additive manufacturing of optical microstructures, yet its ability to regulate the ink droplet morphology is constrained by the intrinsic interplay between ink-substrate wetting conditions, thereby hindering the customizable fabrication of 3D microstructures. Here, a surface energy-confined multi-layer inkjet printing strategy is developed for precisely fabricating curved optical microstructures with tunable size, solid angle, and configuration. The strategy is implemented through custom-engineered layer-by-layer printing on a pre-patterned substrate with spatially defined interfacial energy barriers, enabling the precise construction and integration of distinct optical microdomes (characterized by substrate attachment and uniform curved profiles) at the microscale. Notably, the strategy facilitates the high-throughput printing of diverse topological microdomes, ranging from triangular to hexagonal architectures. The as-fabricated microdomes, featuring precisely engineered morphology and sub-nanometer surface roughness, exhibit integrated light-field manipulation capabilities and unique multifocal characteristics, highlighting their potential for miniaturized optical systems and intelligent imaging devices. Beyond UV-cured polymers, this methodology is extendable to nanomaterial-based micro-3D printing (e.g., colloidal photonic crystal microdomes), opening avenues for more sophisticated optical functionalities. As a proof-of-concept demonstration, a non-imaging multidimensional encryption platform is printed leveraging 3D morphology-tailored optical readout.

Microlens arrays (MLAs) are key components in 3D integrated imaging optical systems, particularly the multifocal MLAs, which provide a new strategy to break through the depth-of-field limitations for 3D imaging. However, the focal lengths of most existing multifocal MLAs that are produced by solid materials are fixed, making it difficult to meet dynamic imaging requirements with a large depth of field. In this article, we innovatively propose dynamically tunable multifocal MLAs using fluid as the lens material, which is integrated into a three-dimensional optofluidic chip fabricated by two-photon 3D printing technology. The fluid multifocal MLAs are realized by filling a microcavity array with flow streams of a gradient refractive index (RI) distribution, which is formed through convection and diffusion between miscible liquids of different RIs. By changing the flow rates, the RI distribution in the microcavity array can be readily regulated; thus, the optical characteristics of the MLAs can be dynamically tuned. The modulation mechanism is revealed by combining theoretical analysis, numerical simulations, and experimental observations. Thanks to the excellent regulatability of fluids by optofluidics, the present fluid MLA offers a wide adjustment range for the focal length, numerical aperture, and focal spot intensity. Especially, it possesses the ability to rapidly switch between different focal planes (flat, concave, and multiple-curved focal planes). Furthermore, the imaging applications of fluid MLAs are demonstrated using fluorescent microparticles and fluorescence-stained cells as samples, which exhibit enhanced magnification and improved clarity. This adaptability supports dynamic sample observation, highlighting the great potential of optofluidic multifocal MLAs for applications requiring large depth-of-field imaging.

Optical microcavities are widely used to confine photons for exciton-polariton formation. However, their compact design often imposes limitations on spatial freedom, particularly in controlling the cavity length with the nanometer precision required for effective coupling with excitons. Existing methods for tuning resonances by integrating cavities with dynamic structures often lack sufficient resolution or a complex operation. Here, we introduce a multiresonant microcavity array that provides a full spectral selection of cavity resonances with a sub-5 nm cavity length variation. We employed this platform to investigate room-temperature polariton formation using gradient core-crown colloidal quantum wells that host highly stable excitons. The strong coupling system exhibits longevity of Rabi oscillations with a quality factor of QR = 3.3 and a large Rabi splitting exceeding twice the thermal losses. Notably, we achieved control of the polariton mixed properties across the cavity arrays on a single substrate. This platform is promising for the development of on-chip polaritonic devices.

Tuning quantum emission to a specific wavelength at room temperature holds significant promise for enhancing secure quantum communication, particularly by aligning with the Fraunhofer lines in the solar spectrum. The integration of quantum emitters with phase-change materials enables emission wavelength modulation, especially when strong field enhancement is present. Antimony telluride (Sb2Te3) exhibits the potential to facilitate this functionality through its support of interband plasmonics and phase-change behavior. In this study, Sb₂Te₃ antennae are designed and fabricated to tune the emission energy of adjacent perovskite quantum dots (QDs) by over 570 meV. The underlying mechanism involves the localized surface plasmons (LSPs) on Sb₂Te₃ nanostructures, which exhibit a surface-enhanced Landau damping process that facilitates the decay of LSPs into electron-hole pairs. The generated hot electrons are then injected into perovskite QDs via the microscopic electron transport process, which can be triggered by the transition of Sb2Te3 from amorphous to a crystalline state, resulting in a significant emission energy shift from 1.64 to 2.21 eV. Furthermore, the emission energy of perovskite QDs on crystalline Sb₂Te₃ nanoantennae can be modulated through DC voltage bias, highlighting the potential for extensive wavelength tunability of quantum emitters integrated with electronic systems.

Nanofabrication, a pivotal technology at the intersection of nanoscale engineering and high-resolution patterning, has substantially advanced over recent decades. This technology enables the creation of nanopatterns on substrates crucial for developing nanophotonic devices and other applications in diverse fields including electronics and biosciences. Here, this mega-review comprehensively explores various facets of nanofabrication focusing on its application in nanophotonics. It delves into high-resolution techniques like focused ion beam and electron beam lithography, methods for 3D complex structure fabrication, scalable manufacturing approaches, and material compatibility considerations. Special attention is given to emerging trends such as the utilization of two-photon lithography for 3D structures and advanced materials like phase change substances and 2D materials with excitonic properties. By highlighting these advancements, the review aims to provide insights into the ongoing evolution of nanofabrication, encouraging further research and application in creating functional nanostructures. This work encapsulates critical developments and future perspectives, offering a detailed narrative on the state-of-the-art in nanofabrication tailored for both new researchers and seasoned experts in the field.

Thermoelectric photodetectors are robust alternatives to photodiodes with applications in extreme environments; however, the poor absorptivity of thermoelectric materials limits their photosensitivity. Here, we take a new look at the traditional thermoelectric materials Sb2Te3 and Bi2Te3 in their recently discovered ability to support interband plasmonic resonances in the visible spectrum. We fabricated nanoresonators directly into the thermoelectric materials to improve their optical absorptance through plasmonic field enhancements, leading to improved photo-thermoelectric conversion. A thermoelectric detector with Sb2Te3 and Bi2Te3 nanostructures demonstrated ∼90 % optical absorptance across the visible spectrum, more than twice that of unpatterned materials. The solid-state device was fabricated on a substrate and exhibited a response time of 160 µs and a specific detectivity of 3.2×106cm Hz12W−1 $\left.3.2{\times}1{0}^{6} \text{cm\,H}{\text{z}}^{1/\right.2} {\text{W}}^{-1}$ . Our demonstration that plasmonic and thermoelectric properties can be exploited within the same material could advance photodetectors and other optoelectronic technologies, such as biosensors, solar cells, and integrated spectrometers.

Silicon photodetectors are highly desirable for their CMOS compatibility, low cost, and fast response speed. However, their applications in the infrared (IR) regime are inherently limited by the intrinsic bandgap of silicon, which limits the detection wavelengths to being below 1.1 μm. Although several methods have been developed to extend silicon photodetectors further in the IR range, these approaches often introduce additional challenges. Here, we present an approach to overcome these limitations by integrating disordered metasurfaces with upconversion nanoparticles, enabling IR detection by silicon photodetectors. The disordered design consisting of hybrid Mie-plasmonic cavities can enhance both the near-field localization and wide-band light absorption. The measured responsivity of the disordered element for 1550-nm laser is 0.22 A/W at room temperature, corresponding to an external quantum efficiency of 17.6%. Our design not only enhances the photocurrent performance, but also extends the working wavelength of silicon photodetectors to IR spectrum applications.

Glass is widely used as an optical material due to its high transparency, thermal stability, and mechanical properties. The ability to fabricate and sculpt glass at the nanoscale would naturally expand its application domain in nanophotonics. Here, we report an approach to print glass in three dimensions with nanoscale resolutions. We developed Glass-Nano, an organic-inorganic hybrid resin containing silicon elements. Using this high-resolution resin, three-dimensional (3D) photonic crystals (PhCs) were printed with two-photon lithography. After printing, the structures were heated to high temperatures in air to remove organic components and convert the remaining material into silica glass. 3D glass PhCs with periodicities as small as 260 nanometers were obtained after sintering at 650°C. The 3D glass PhCs exhibit ~100% reflectance in the visible range, surpassing the typical reflectances observed from similar structures in low–refractive index materials. The quality of PhCs achieved is observed in both electron microscopy and the excellent agreement with band structure calculations of idealized structures.

Understanding state-dependent crystallisation kinetics is important for the modelling and design of phase change material (PCM)-based devices, such as multi-level switches. We show how the level of amorphousness (disorder) of antimony-telluride (Sb2Te3) can be controlled using pulsed laser heating, and that the recrystallisation temperature strongly depends on the local atomic configurations in the amorphous structure. Indeed, when Sb2Te3 is amorphized with higher laser powers, its subsequent recrystallisation temperature increases by up to 23 degrees C yet, and counterintuitively the recrystallisation activation energy decreases. This leads to shorter minimum recrystallisation times. This effect is important because it provides a means to switch PCM devices at higher rates through a catalyst-like effect. The optical properties of Sb2Te3 can be gradually tuned by the level of crystallographic disorder. The amorphousness of PCMs provides a further degree-of-freedom to achieve multi-level programmability and tune the switching energy of devices.

Interband plasmons (IBPs) enable plasmonic behavior in nonmetallic materials, such as semiconductors. Originating from interband electronic transitions, IBPs are characterized by negative real permittivity that can extend into deep ultraviolet (DUV) spectrum, as demonstrated using silicon. However, the practical applications of IBPs are limited by their inherently broad resonances. In this study, we address this limitation by hybridizing the localized plasmon resonance of silicon nanostructures with the Fabry-Perot resonance of a SiO2 dielectric layer atop a silicon substrate. This design achieves a simulated quality factor (Q-factor) of similar to 43, with experimental measurements yielding a Q-factor of 37 at similar to 4.6 eV within the DUV region. Furthermore, we demonstrate a 5.4-fold enhancement in DUV absorption for lignin-modified polyethylene glycol films when integrated with the hybridized DUV cavity, showcasing the potential for UV blocking applications. Our findings offer a versatile platform that can be adapted to other IBP systems and open new opportunities in UV-specific applications.

Optical imaging systems have greatly extended human visual capabilities, enabling the observation and understanding of diverse phenomena. Imaging technologies span a broad spectrum of wavelengths from x-ray to radio frequencies and impact research activities and our daily lives. Traditional glass lenses are fabricated through a series of complex processes, while polymers offer versatility and ease of production. However, modern applications often require complex lens assemblies, driving the need for miniaturization and advanced designs with micro- and nanoscale features to surpass the capabilities of traditional fabrication methods. Three-dimensional (3D) printing, or additive manufacturing, presents a solution to these challenges with benefits of rapid prototyping, customized geometries, and efficient production, particularly suited for miniaturized optical imaging devices. Various 3D printing methods have demonstrated advantages over traditional counterparts, yet challenges remain in achieving nanoscale resolutions. Two-photon polymerization lithography (TPL), a nanoscale 3D printing technique, enables the fabrication of intricate structures beyond the optical diffraction limit via the nonlinear process of two-photon absorption within liquid resin. It offers unprecedented abilities, e.g. alignment-free fabrication, micro- and nanoscale capabilities, and rapid prototyping of almost arbitrary complex 3D nanostructures. In this review, we emphasize the importance of the criteria for optical performance evaluation of imaging devices, discuss material properties relevant to TPL, fabrication techniques, and highlight the application of TPL in optical imaging. As the first panoramic review on this topic, it will equip researchers with foundational knowledge and recent advancements of TPL for imaging optics, promoting a deeper understanding of the field. By leveraging on its high-resolution capability, extensive material range, and true 3D processing, alongside advances in materials, fabrication, and design, we envisage disruptive solutions to current challenges and a promising incorporation of TPL in future optical imaging applications.

Caustics occur in diverse physical systems, spanning the nano-scale in electron microscopy to astronomical-scale in gravitational lensing. As envelopes of rays, optical caustics result in sharp edges or extended networks. Caustics in structured light, characterized by complex-amplitude distributions, have innovated numerous applications including particle manipulation, high-resolution imaging techniques, and optical communication. However, these applications have encountered limitations due to a major challenge in engineering caustic fields with customizable propagation trajectories and in-plane intensity profiles. Here, we introduce the compensation phase via 3D-printed metasurfaces to shape caustic fields with curved trajectories in free space. The in-plane caustic patterns can be preserved or morphed from one structure to another during propagation. Large-scale fabrication of these metasurfaces is enabled by the fast-prototyping and cost-effective two-photon polymerization lithography. Our optical elements with the ultra-thin profile and sub-millimeter extension offer a compact solution to generating caustic structured light for beam shaping, high-resolution microscopy, and light-matter-interaction studies.

Three-dimensional (3D) imaging enables high-precision and high-resolution axial positioning, which is crucial for biological imaging, semiconductor defect monitoring, and other applications. Conventional implementations rely on bulky optical elements or scanning mechanisms, resulting in low speed and complicated setups. Here, we generate the double-helix (DH) point spread function with an all-dielectric metasurface and thus innovate the 3D imaging microscope (hence dubbed meta-microscope), both in 4f and 2f imaging systems. The 4f-meta-microscope with a numerical aperture of 0.7 achieves an axial localization accuracy below 0.12 mu m within a 15.47 mu m detection range, while the 2f-DH meta-microscope with a numerical aperture of 0.3 shows a 1.12 mu m accuracy within a 227.33 mu m range. We also demonstrate single-shot and accurate 3D biological imaging of the mouse kidney tissue and peach anther, providing a comprehensive and efficient approach for 3D bioimaging and other applications through a single-shot 3D meta-microscope.

A radiation thermopile detector that converts radiant thermal energy into electricity is capable of remote temperature measurement without the need for a cooling system. However, due to its operating mechanism, its active area needs to be larger than the wavelengths of thermal radiation, i.e. >10 mu m. Here, we report calculation results of a metamaterial thermopile that operates beyond the optical diffraction limit. The metamaterial thermopile has a physical active area of only seven square microns but absorbs thermal energy from the environment equivalent to that of a significantly larger detector owing to the large absorption cross-section of the metamaterial elements. The metamaterial absorbs thermal radiation emitted from the surrounding media, creating a thermal gradient across a silicon nanowire, resulting in thermoelectric conversion. We numerically evaluated the responsivity and specific detectivity of the metamaterial thermopile at temperature ranging from 273 to 373 K. The calculated specific detectivity of the metamaterial thermopile was 2.38 x 10(7) (cm center dot Hz(1/2)center dot W-1/2). This metamaterial thermopile that enables highly miniaturized thermometry sensors surpassing the optical diffraction limit, opens new avenues for microscale temperature measurement, leading to new discoveries in physics and thermodynamics.

Efforts to increase the number of filters are driven by the demand for miniaturized spectrometers and multispectral imaging. However, processes that rely on sequential fabrication of each filter are cost ineffective. Herein, we introduce an approach to produce at least 16 distinct filters based on a single low-resolution lithographic step with minimum feature size of 0.6 μm. Distinct from grayscale lithography, we employ standard binary lithography but achieve height variations in polymeric resist through a post-development reflow process. The resulting transparent polymeric films were incorporated in Fabry–Perot cavity structures with cavity thickness ranging from 90 to 230 nm to produce transmittance across the visible spectrum. This binary lithography and reflow (BLR) process demonstrates control of the dielectric layer thickness down to ∼15 nm. This new process provides a cost-effective alternative to traditional techniques in fabricating microscopic transmission filters, and other applications where precise thickness variation across the substrate is required.