Optical skyrmions are topological textures of electromagnetic fields with promising applications in information processing, transport, and storage. Exquisitely tailoring the optical fields of diverse physical quantities has expanded the family of skyrmions, yet such skyrmions only exhibit a single-quantity texture in free space. Herein, dual skyrmionic textures concurrently portraying spin and Poynting vectors are unveiled in the tight focus of an annular second-order circularly polarized vortex beam. The focal electric and magnetic fields exhibit an elongated and identical spatial distribution but a phase difference of π/2, leading to dual skyrmionic textures with vector orientations that are either opposite or identical, depending on the handedness of the incident beam. Unlike conventional optical skyrmions that are exclusively regarded as quasiparticles distributed in a two-dimensional plane, a skyrmionic tube structure that extends over a longitudinal depth approaching 10λ while preserving its topology is demonstrated. Our Letter enhances the comprehensiveness of optical skyrmions and paves the way toward their practical applications by bolstering skyrmion-matter interactions.

Structured light projection serves as a commonly utilized technique for depth perception in facial recognition and anti-counterfeiting identification systems. As a core component in such optical arrangements, diffractive optical elements (DOEs) effectively transform collimated laser beams into uniformly illuminated dot patterns through precise light field modulation. However, when integrating DOEs with vertical cavity surface emitting laser arrays (VCSELs), collimated light from VCSELs exhibits multiple oblique incident angles beyond the normal 0 degrees angle. Conventional DOEs suffer from degraded diffraction efficiency and intensity uniformity under large-angle illumination. This study introduces an end-to-end inverse design method by directly linking the metasurface to the reconstructed diffraction intensities, and employs a figure of merit (FOM) to guide the update of the metasurface structured parameter. The optimized metasurface achieves wide-angle structured light generation spanning a 49.8 degrees & times; 56.1 degrees field of view (FOV), preserving super optical performance with diffraction efficiency > 83% and uniformity error < 0.1 for incident angles within +/- 9 degrees in both x-and y-directions. Our proposed method is promising for advanced applications, including 3D metrology, holography, and beam shaping, benefiting from the multi-objective optimization.

Although conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) are pivotal for flexible organic electronics, achieving tunable conductivity in high-resolution micro/nanoarchitectures remains a significant challenge. Conventional methods like inkjet writing and laser ablation not only offer limited resolution but also fail to provide the dynamic conductivity control required for advanced applications. To address these challenges, we developed a two-step nanofabrication strategy to produce PEDOT-based nanoarchitectures with tunable conductivities. A femtosecond direct laser writing technique was utilized to firstly create 3,4-ethylenedioxythiophene (EDOT)-based pH responsive nanostructures, and subsequently chemical oxidation was employed to convert EDOT-based nanostructures into conductive PEDOT-based ones, which enabled high-resolution conductive nanostructures with feature sizes as small as 250 nm and conductivity of 679 S m-1. Additionally, the structures exhibited tunable conductivity ranging from 454 S m-1 (pH = 13) to 1041 S m-1 (pH = 1), due to the swelling/contraction of the pH responsive acrylate-functionalized derivative matrix. This work demonstrates a scalable strategy for creating high-resolution, pH-stimuli-responsive conductive polymer-based nanostructures such as PEDOT nanostructures, offering significant potential for advanced applications in nanoelectronics and biosensors.

3D printing of conducting polymers has garnered increasing interests owing to their emerging potentials in nanoelectronics, nanophotonics and bioelectronics. Even though direct laser printing techniques surpassing conventional inkjet printing offer nanoscale resolution and advanced 3D capability, disordered molecular main chain, insulating side chain and irregular phase separation impose additional energy barriers to charge transport kinetics in photocurable polymer framework, thereby compromising overall conductivity performance of as-fabricated devices. Here, we develop a novel poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) hydrogel photoresin for realizing highly conductive organic 3D nanostructures by using multiphoton direct laser printing technique. High pulse energy of the polarized femtosecond laser has been shown to induce the arrangement of the PEDOT:PSS nanofibrils and side chains of PSS detaching from PEDOT, which enables fabricated nanowires with a record-high conductivity of approximately 1010 S/cm and a deep sub-diffraction limit feature size of 78 nm. The facile printability allows sophisticated 3D bioelectronics to be in-situ fabricated and integrated with microfluidic chips, enabling precise sensing water contents. Leveraging its biocompatibility, we further demonstrate 3D bioelectronic sensors for real-time monitoring of ethanol yields throughout the yeast fermentation process.

With the rapid advances of optical information technology, numerous optical systems in both scientific and industrial fields are pursuing a resolution that surpasses the classical diffraction limit. Super-resolving pupil filters, whose transmittance or phase can be spatially modulated, have attracted intense interest for squeezing the focal spot of optical systems through wavefront manipulation, and have also been implemented in the fields of optical microscopy, optical storage, telescopes, etc. However, all the previously reported super-resolving pupil filters are tailored exclusively to specific optical systems with fixed focal lengths, rendering them incompatible with zoom or variable-focus optical platforms. In this work, we introduce a multi-adaptive super-resolving pupil filter that retains sub-diffraction-limited performance across a range of variable focal lengths. Such a pupil filter is composed of concentric annular belts in a binary phase configuration, designed via a two-step optimization algorithm and fabricated by using the ultraviolet optical lithography technique. Both numerical simulation and experimental results demonstrate that the sub-diffraction-limited focal spot can be consistently yielded at the designed wavelength of 633 nm when the super-resolving pupil filter is paired with plano-convex lenses of 50 mm,75 mm,100 mm, and 150 mm focal lengths, respectively. As a proof-of-concept demonstration, we integrate the filter into an optical imaging system and experimentally verify its resolution enhancement performance over the full focal-length range. Owing to its planar geometric structure and negligible insertion loss, the proposed multi-adaptive super-resolving pupil filter offers a practical way for the development of super-resolution zoom microscopy and zoom telescopes.

Laser-based three-dimensional (3D) metal printing emerges as a transformative technology that enables fabrication of functional components for applications ranging from aerospace and automobile industries1 to micro-electronics2 and photonics3. Conventional approaches typically rely on high-power lasers to join metallic composites into complex geometries4,5. In addition to the unbearable cost of high-power lasers, however, intensive laser heating of the absorptive metallic composites parasitically causes thermal diffusions6-9, which limits printing resolution and surface roughness to sub-micron levels10-20 and thus impair their electrical and optical performances. Here, we develop thermoplasmonic laser printing (TPLP), a technique that transduces diffusive heat into a confining Coulombic potential to directly assemble metallic composites into 3D nanostructures. Unlike existing nanoprinting strategies10-15 where pulsed lasers with peak power up to 0.1 MW scale are required, our method can be operated using continuous-wave lasers at powers of 100 μW scale, which is 9 order-of-magnitude lower. We demonstrate 3D metal nanoprinting with finest feature size down to 86 nm, surface roughness as low as 1.6 nm and electrical conductivity up to 0.1×107 S/m, which are inaccessible by conventional methods. Our method opens a cost-efficient pathway to fabricate miniaturized 3D metallic devices for multifarious optoelectronic applications.

Polarization imaging has the powerful ability to detect unique features invisible to human eyes, which is challenging for conventional intensity imaging systems. Metasurface emerges as a transformative platform for compact polarization imaging systems, but prior strategies suffer from limited imaging field-of-view (FOV) and coarse-grained polarization pixels. Here, we demonstrate a meta-grating-lens (MGL)-based monolithic polarization camera achieving 14° FOV and real-time full-Stokes polarization imaging in the near-infrared region. The optimized MGL exhibits >60% focusing efficiency with <3% zeroth-order noise, enabling simultaneous polarization analysis, beam-splitting, and imaging functionalities in a fine-grained pixel level. This synergistic design enables both efficient light utilization and accurate polarization reconstruction. The proposed polarization camera has the potential to unlock wide range of applications including autonomous navigation, biomedical diagnostics, and even compact Muller matrix imaging systems.

Artificial nanostructures with ultrafine and deep-subwavelength features have emerged as a paradigm-shifting platform to advanced light-field management, becoming key building blocks for high-performance integrated optoelectronics and flat optics. However, direct optical inspection of integrated chips remains a missing metrology gap that hinders quick feedback between design and fabrications. Here, we demonstrate that photothermal nonlinear scattering microscopy can be used for direct imaging and resolving of integrated optoelectronic chips beyond the diffraction limit. We reveal that the inherent coupling among deep-subwavelength nanostructures supporting leaky resonances allows for the pronounced heating effect to access reversible nonlinear modulations of the confocal reflection intensity, yielding optical resolving power down to 80 nm (~λ/7). The versatility of this approach has been exemplified by imaging silicon grating couplers and metalens with minimum critical dimensions of 100 nm, as well as central processing unit chip with 45-nm technology, unfolding the long-sought possibility of in situ, nondestructive, high-throughput optical inspection of integrated optoelectronic and nanophotonic chips.

Topological properties of energy flow of light are fundamentally interesting and have rich practical applications in optical manipulations. Here, skyrmion-like structures formed by Poynting vectors are unveiled in the focal region of a pair of counter-propagating cylindrical vector vortex beams in free space. A N\'eel-Bloch-N\'eel skyrmion type transformation of Poynting vectors is observed along the light propagating direction within a volume with subwavelength feature sizes. The corresponding skyrmion type can be determined by the phase singularities of the individual components of the coherently superposed electromagnetic field in the focal region. This work reveals a new family member of optical skyrmions and may introduce novel physical phenomena associated with light scattering and optical force.

The compactness and particular optical design make metasurface a competitive candidate for holographic display and storage. Recently, the selection and optimization for the used metasurface structures and types have become research spots. Now the most researched and demonstrated meta-holograms are often based on discrete structures, which can achieve high efficiency but comparatively narrow working bandwidths or a wide wavelength range but low power efficiency. Therefore, contemporary meta-holograms struggle for realizing simultaneous broadband and high efficiency. In this paper, all-dielectric quasi-continuous metasurfaces composed of nanostrips are introduced to expand the operating bandwidth for high efficiency meta-holography. Benefiting from the associated Pancharatnam–Berry phase, the nanostrips with spatially orientation angles continuous changes can realize arbitrary phase modulation. For the first time, the average power efficiency of a meta-hologram is experimentally measured to be 56.63% over a broad wavelength band ranging from 500 to 1000 nm. In addition, based on this kind of all-dielectric quasi-continuous nanostrips, we also design and experimentally achieve multicolor three-dimensional (3D) holographic images. Actually, such all-dielectric quasi-continuous methodology proposed here can be used to design other functional meta-devices, including optical metalens, nanoprinting, and information encryption.

光学斯格明子为实现结构光场以及时空光场的拓扑属性提供了新的研究方法与研究思路。本文在4π聚焦系统中，通过对两对入射柱矢量光束进行偏振与相位调控，实现了聚焦光场纵向分量与横向分量的独立控制，在焦平面上得到了Néel型与Bloch型的电磁矢量光学斯格明子。在4π聚焦系统内调控两对反向传播的径向偏振光时，焦平面处将产生Néel型的电场矢量斯格明子。将其中一对替换为角向偏振光时，焦平面处将同时产生Bloch型的电场矢量斯格明子与相位超前π/2的磁场矢量斯格明子。本工作为进一步研究自由空间中微纳尺度电磁矢量光学斯格明子与物质的相互作用提供了理论基础。

Featured with its extraordinary super-resolution capability, the advent of stimulated emission depletion (STED) lithography has allowed for vastly reduced minimum feature size of a single pixel down to the deep sub-diffraction scale so as to produce unprecedented nanofeatures. However, the anticipated sub-diffraction pixel pitch down below 100 nm remains out of reach due to redundant polymerization of adjacent exposures at a short distance, so called memory effect. In this work, a nanoprinting-at-expansion/employments-at-recovery strategy is applied in the dual-beam STED lithography technique to surmount the memory effect and break adjacentexposure limit imposed on minimizing the pixel pitch. The implementation of a femtosecond laser at a wavelength of 532 nm, the same as the inhibition laser beam, working as the initiation laser beam, can drastically reduce the saturated inhibition laser intensity by 74% for abating redundant polymerization subjected to multiple exposures in realizing nanoscale pixel pitch. The adjacent-exposure zone can be separated by isotropically expanding an elastic PDMS substrate for further diminishing redundant polymerization. Applying stretching ratio of 30%, a minimum super-resolved nanodots pixel pitch of 96 nm was achieved with single-dot size of 34 nm on both planar and hierarchical substrate, which offers a record-close distance for printing adjacent pixels. With its nanometer discernibility, this method holds great promise for future versatile utilization in advanced nanoimprinting, high density data storage, etc.

: Featured by the capability of multi degree-of-freedom light-field manipulations while reserving high spatial resolution, multifocal laser arrays have been widely applied in femtosecond laser micro/nanofabrication, optical trapping, and so forth. Yet, due to the relatively lower axial resolution of single focuses within the array in comparison with the lateral resolution of their own, multifocal laser array has been refrained from isotropic 3D nanofabrication. Herein, we propose a feasible method for generation of axially super-resolved multifocal array with quasi-spherical focal spots. In particular, quasi-spherical multifocal array is optically synthesized via precise modulation on the coherent superposition of the orthogonal radially polarized beam (RPB) and azimuthally polarized beam (APB) states in the focal region based on annular amplitude modulation. We show theoretically the generation of quasi-spherical multifocal array with a high uniformity up to 99 % . The average axial and lateral full-width-half maximum (FWHM) of the focal array are measured to be 0.76 λ with the standard deviations in the axial and lateral directions being 0.005 λ and 0.019 λ , respectively. The presented strategy for synthesis of quasi-spherical multifocal array with high uniformity paves the way for high-precision laser fabrication of 3D micro/nano devices. Overview: Featured by the capability of multi degree-of-freedom light-field manipulations while reserving high spatial resolution, multifocal laser arrays have been widely applied in femtosecond laser micro/nanofabrication, optical trapping, etc. However, for lens diffraction, the smaller momentum spread along the optical axis with respect to that in the transverse direction could introduce a larger position spread in real space, which in turn leads to lower axial resolution than the transverse resolution. The anisotropy of the focused laser beam, inherent regardless of paraxial or tight-focusing cases, has been a great hurdle for laser printing of functional microdevices with precise control on feature size and improved mechanical performances. To this end, in this research, a feasible method for generation of isotropic focused laser beam with quasi-spherical 3D point spread function (PSF) is developed based on vectorial light field modulation. We demonstrate that through simultaneous implementation of phase modulation and amplitude modulation, homogeneous multifocal array with quasi-spherical focal spots can be generated. Particularly, with the use of a well-designed annular mask, the suppression on the axial spread of field is accomplished via accurate control on the coherent superposition of the orthogonal radially polarized beam (RPB) and azimuthally polarized beam (APB) in the focal region since the depolarized axial component of the AP beam vanishes in vicinity of the gaussian focus even under tight focusing condition. Using the proposed method, isotropic 3D PSF with identical axial and transverse FWHM of 0.71 λ is achieved. Meanwhile, based on iterative phase retrieval algorithm, phase-only holograms are designed and employed transforming the incident wavelet as the summation of sub-wavelets, yielding multiple converging sites in 3D space, thereby generating the multifocal array. We further present the synthesis of quasi-spherical multifocal array. A high uniformity up to 99 % for a 10-by-10 multifocal array, in which the single focus elements share near-identical axial and transverse FWHM, being 0.76

Metasurfaces can enable powerful manipulations for electromagnetic waves, thus many exotic functionalities have been realized. However, constrained by the complexity of metasurface-modulated complex amplitudes (amplitude and phase), the design of complex-amplitude metasurfaces sets a high threshold for researchers because of the requirement of plenty of specialized knowledge. In this paper, a deep learning scheme that uses a forward surrogate network to assist complex-amplitude metasurface design is proposed. The model is simple to construct and easy to converge in training. Accordingly, two complex-amplitude multiplexing devices, which can simultaneously display a nanoprinting image at the device surface and one/two holographic images in the far field, are designed with the proposed network using the cross-shaped meta-atom. The results show that the demonstrated scheme can be used to design the complex-amplitude metasurface devices easily and effectively once training of the network is completed, and the single-layer smooth structure holds the advantage for the fabrication. The proposed method here is promising to realize designs of more complex-amplitude meta-devices, multi-polarization, and multi-wavelength multiplexing meta-devices.

本文提出了一种基于空间填充曲线的超构表面结构，利用理论分析、数值仿真的方法研究了该超构表面的近场电磁特性，实现了高度局域及高品质因子（Q-factor）的多阶人工局域表面等离激元共振（spoof plasmon resonances）。我们发现采用不同结构形状和尺寸的空间填充曲线均可产生共振频率规则分布的多阶谐振模式，通过调整结构的等效波导长度，可同时获得高的谐振波长/结构尺寸压缩比与高品质因子。空间填充曲线所支持的人工局域表面等离激元由磁偶极子与电偶极子模式交替支持；其余参数不变的情况下改变空间填充曲线的分布形式，结构所支持的表面等离激元的谐振特性不受形状曲折的影响，而只与等效波导总长度有关。此外，近场模式的强度分布随着空气波导的走向而改变，可根据实际需求对结构进行特定排布。本文的研究结果对设计基于空间填充曲线的小型化高品质因子电磁谐振器件具有重要的指导意义。

The advanced direct laser printing of functional devices with tunable effective index is a key research topic in numerous emerging fields, especially in micro-/nano-optics, nanophotonics, and electronics. Photosensitized nanocomposites, consisting of high-index materials (e.g., titanium dioxide, TiO2) embedded in polymer matrix, are emerging as attractive platforms for advanced additive manufacturing. Unfortunately, in the currently applied techniques, the preparation of optically functionalized structures based on these photosensitized nanocomposites is still hampered by many issues like hydrolysis reaction, high-temperature calcinations, and, especially, the complexity of experimental procedures. In this study, we demonstrate a feasible strategy for fabricating micro-/nanostructures with a flexibly manipulated effective refractive index by incorporating TiO2 nanoparticles in the matrix of acrylate resin, i.e., TiO2-based photosensitized nanocomposites. It was found that the effective refractive index of nanocomposite can be easily tuned by altering the concentration of titanium dioxide nanoparticles in the monomer matrix. For TiO2 nanoparticle concentrations up to 30 wt%, the refractive index can be increased over 11.3% (i.e., altering from 1.50 of pure monomer to 1.67 at 532 nm). Based on such a photosensitized nanocomposite, the grating structures defined by femtosecond laser nanoprinting can offer vivid colors, ranging from crimson to magenta, as observed in the dark-field images. The minimum printing width and printing resolution are estimated at around 70 nm and 225 nm, indicating that the proposed strategy may pave the way for the production of versatile, scalable, and functionalized opto-devices with controllable refractive indices.

Here, we demonstrate a flat nanofocalizer for converging light field into a uniform subwavelength light spot array based on the fractional Talbot effect by developing a direct laser writing technique with 3D fabrication precision. The fractional Talbot effect endows the device with the merits of high compression ratio and modular design capability for transforming a plane wave into arrayed light focal spots. By combining a synergistic laser printing technique, we introduce a buffer layer for improving the fabrication precision of structural height in favor of accurately manipulating the phase delay. For a given light wavelength at 750 nm, by precisely producing a nanofocalizer consisting of periodic unit elements with the dimensions of 300(width)×600(length)×585(height)nm, we have achieved 5×6 light spot array with modular design, while the full width at half-maximum of a single focused light spot can be reduced to ∼0.82λ. Our research may pave the way for realizing subwavelength optical devices capable of being readily integrated to existing optical systems.

In this paper, a two-photon polymerization system built using a femtosecond laser was used to fabricate a microfiber long-period fiber grating (MLPG). The system uses a computer to control the three-dimensional displacement platform to complete the structure production, is programmable to realize the automatic grating production, and monitors the grating production process throughout the process. To complete the fabrication of the MLPG, the two-photon polymerization of the photoresist periodically occurs on the surface of the fiber. Compared with the traditional manufacturing method, the grating manufacturing method based on two-photon polymerization did not depend on the changes of the fiber substrate. The long-period grating can be flexibly manufactured on the outer surfaces of different types of fibers. As an example, we fabricated eight grating blocks with a 95 mu m period on a microfiber with 6. 9 mu m diameter. At 1331 nm, a transmission spectrum loss peak of 13.5 dB is observed. The experimental results show that the temperature and refractive index sensitivities of the MLPG are as high as 1.39 nm/degrees C and 2207.89 nm/RIU( RIU is the unit refractive index), respectively.

Recent demonstrations of metasurfaces present their great potential to implement flat and multifunctional optical elements, which are accomplished with the designs of planar optics and micro-/nano- fabrications. Integrating metasurfaces in three dimensions has manifested drastically increasing advantages in manipulating light fields by extending design freedom. However, fabricating three-dimensional metasurfaces remain a tough challenge due to the lack of stereo printing protocols. Herein, we demonstrate laser nanoprinting of floated silver nanoparticle array in transparent hydrogel films for 3D metasurface to achieve color patterning. It is found that spatially resolved nanoparticles can be produced through laser induced photoreduction of silver ions and robustly anchored to the gel backbones by a focused femtosecond laser beam within a pH-responsive smart hydrogel matrix. With the aid of expansion properties of the pH-responsive hydrogel, repetitive coloration of the patterned plasmonic nanoparticle array over a wide spectrum range is achieved via reversible regulation of nanoparticle spacing from 550 to 350 nm and vice versa. This approach allows broadband 3D color-regulation in nanoscale for applications in active spectral filtering, information encryption, security tagging and biological colorimetric sensing, etc.