Radiative cooling is a groundbreaking technology for sustainable temperature regulation to combat global warming and the urban heat island effect. Traditional optimization algorithms for cooling system structures are often brute-force and even limited to local optimal solutions. Here, we propose a joint simulation method based on a multilayer perceptron (MLP) and a convolutional neural network (CNN) with position encoding (PE), namely the hybrid MLP-CNN model with PE. This method can significantly reduce simulation time, avoid getting trapped in local optima, and accurately predict the optical response and radiative cooling power of the structure. Applying PE enables the MLP model to learn the relationship between structural parameters and optical response more quickly and effectively, reducing loss during training and more minor root mean square error (RMSE) and mean relative error (MRE) during testing. In addition, the residual network can reduce the problem of overfitting in the network. Compared to using only an MLP, the hybrid MLP-CNN with PE model can effectively reduce loss and achieve more accurate prediction outputs. The hybrid model is much faster than traditional electromagnetic simulations, taking only 1% of the time, and the model dramatically reduces the time needed to predict the optical response of structures and effectively decreases the cost of designing optical devices. Utilizing this hybrid model not only avoids the potential drawbacks of being limited to suboptimal solutions and significantly reduces the simulation time, but also effectively predicts the optical response of the device. This approach can demonstrate remarkable adaptability in optimizing geometric parameters of various optical apparatuses, including polarization converters, beam splitters, metalens, and other two-dimensional nanostructures.

The entities in the knowledge graphs are generally categorized into concepts and instances, where each concept is used to represent the abstraction of a set of instances with common properties. Most previous Knowledge Graph Embedding methods tend to treat them in the same way by projecting them into low-dimension space as vector points without explicitly distinguishing them, therefore ignoring the potential specification of concept. Some recent studies address this problem by modeling each concept as a sphere rather than a vector point. However, the isotropy of the sphere is less capable of modeling the semantic abstraction of concepts, as well as the complex relations between concepts and instances. To solve this problem, we propose to model concepts using geometric shapes with anisotropy to enrich the representation power of concepts. Two algorithms, named as TransEllipsoid and TransCuboid, are presented to project each concept as an ellipsoid and a cuboid in embedding space respectively. The anisotropy of concept embedding is learned by allowing the length of the axes of the ellipsoid or the edges of the cuboid to vary across different dimensions. Experimental results on three real-world datasets show that modeling the anisotropy of concept embedding would significantly benefit not only the learned representations of concepts but also the corresponding instances. The visualization of embedding results reveals human-intuitive relative positions between concepts and instances and provides potential interpretability for the transitivity of isA relations.

Reconfigurable photonic devices integrated with silicon waveguides are important building blocks for future on-chip photonic circuits. In this paper, we focus on the mode order conversion in silicon waveguides with non-volatile reconfigurable capability. Deformed phase change material Sb 2 Se 3 (antimony triselenide) stripes are introduced at the edges of the functional region to provide the refractive index difference required by mode conversions. The shapes of stripes are inversely designed by a gradient-based iterative optimization strategy with 57 (19) iterations for TE0-to-TE1 (TE0-to-TE2) mode converter. The footprint of the functional region is as compact as square center wavelength. In the crystalline phase, TE0-to-TE1 and TE0-to-TE2 mode conversions are realized with conversion efficiencies of 98.5% and 96.3% at a center wavelength of 1550 nm, respectively. While in the amorphous phase, the input TE0 mode directly passes through the functional region with efficiencies of 93.0% and 92.4%, respectively. The output mode can be reconfigured by changing the phase of Sb 2 Se 3 stripes. Moreover, after introducing ±10 nm geometrical deviations to the perfect Sb 2 Se 3 stripe design, corresponding red and blue shifts of conversion efficiency spectra can be observed, and the simulation results reflect the reasonable robustness of the proposed mode converters.

Smart windows with high visible transmission can control the absorption or transmission spectrum of solar irradiation based on seasonal variations and personal preferences, allowing buildings to save energy. However, it is a considerable challenge to design a metasurface with high solar modulation ability (ΔAsol), integral luminous transmittance (Tlum), transmission light's color rendering index (Ra) and simple structure for smart windows. In this work, we design and optimize the asymmetric-structured multilayer and micro-nano array by applying the method of scanning parameters and fully-connected network methods. The optimization results show that ΔAsol and Tlum negatively correlate when the transmitted light of these two structures has a high Ra. This conclusion of designing high-performance asymmetric-structured metasurfaces provides essential guidance for designing future smart windows.

Electrochromic windows regulate the transmission and absorption of sunlight according to environmental conditions and personal preferences, resulting in energy conservation. However, developing smart windows that can independently modulate visible and infrared (IR) radiation remains a significant challenge. This paper presents a multilayer film structure for electrochromic windows based on the electro-optic dielectric material of 4-dimethyl-amino-N-methyl-4-stilbazoliumtosylate (DAST), and the film modulates visible and IR light individually. The refractive indices of multilayer DAST films change when different bias voltages are applied, which alters the structure's impedance and selectively modulates electromagnetic wave transmission. Simulation results indicate that the smart window can independently modulate the integrated visible transmittance (Tvis) and integrated infrared transmittance (TIR) at four different bias voltages (-20 V to + 20 V). The modulation ranges for Tvis and TIR are 72.5% to 92.3% and 46.1% to 95.2%, respectively, and the theoretical results surpass those of recent works. A fully-connected network with position coding is employed here, and simulation time is reduced based on truth prediction data. The multilayer structure proposed enables independent modulation of visible and IR light, making it a promising candidate for smart windows since it is lithography-free, large-area compatible, and polarization-independent.

Spectral control of light in the visible range is one of the fundamental topics in optical applications. Micro-electro-mechanically systems (MEMS) combine with metamaterial structures can further enrich the optical function. Here, a plasmonic metamaterial structures based on MEMS consist of the top metal film and bottom metal slab separated by a dielectric layer was proposed to achieve an electrically switchable metamaterial absorber (MMA). Each metamaterial unit cell is composed of an electrically driven suspended metal film and bottom metal substrate, which can perform independent MEMS functions. Full-wave numerical simulations demonstrated that the shifting of the absorption peaks of the spectrum can be achieved in the visible range. The absorption modulation ratio above 60% can be achieved at wavelengths near 570 nm and 640 nm, provided that the full distance (50 nm) between the top suspended metal film and bottom metal slab can be 100% modulated, which can be easily realized via current MEMS technology. This paves the way for MEMS integrated metamaterial absorber as a platform for reconfigurable optics and optical switching.

In this paper, we present a scheme for achieving broadband efficient beam splitting based on homogeneous ultra-thin metasurfaces, which is composed of an ultrathin dielectric spacer sandwiched between periodic arrays of identical rectangular metal resonators and an optically thick metal film. Based on this scheme, three beam splitters for incident wavelengths in the ultraviolet (UV), visible, and infrared (IR) are designed and investigated numerically. Although these beam splitters exhibit polarization-dependent optical responses, each one still has an operational band in which the conversion efficiency remains above 90 % for any polarization incidence. The operational band is respectively 250–299 nm, 478–574 nm, and 1411–1700 nm for these three metasurface-based beam splitters. Moreover, we propose a dual-band beam splitter and a four-channel beam splitter based on this metasurface with MIM configuration. The operational window of the dual-band beam splitter respectively locates in the visible and infrared regions.

Lenses are an important part of modern optical systems. We propose metalenses with bifocal spots, which realizes the beam focusing with controllable intensity ratio and free deflection of the bifocal spots. The metalens consists of an array of titanium dioxide (TiO2) nanopillars, which can provide two different propagation phases for x-linear polarization (XLP) and y-linear polarization (YLP) incidence, respectively. Therefore, by precisely choosing the size of the nanopillars, it is possible to produce two different focal spots for the two orthogonal input polarized light. And the intensity of the two focal points can be adjusted by changing the polarization angle of the incident light. Superimposing the initial phase distribution of the metalens and the phase distribution of the beam deflector metasurface enables multi-dimensional adjustment of the two focal points and realizes the free deflection characteristics of the metalens. The deflection angle of the focal spot is close to the theoretical deflection angle. In addition, multiple superposition can produce more deflection angles or deflect the focus to a two-dimensional plane. The method of controlling the targeting phase of the metalens by superimposing additional phases gives us the ability to fully manipulate the phase and wavefront of the metalens, providing a new idea for the continuous angle change of future optical lenses.

The bound state in the continuum (BIC) has paved a new way to achieve excellent localization of the resonant mode coexisting with a continuous spectrum in the metasurface. Here, we propose an all-dielectric metasurface consisting of periodic pairs of asymmetric crosses that supports multiple Fano resonances. Due to the sufficient degrees of freedom in the unit cell, we displaced the vertical bars horizontally to introduce in-plane perturbation, doubling the unit cell structure. Dimerization directly resulted in the folding of the Brillouin zone in k space and transformed the BIC modes into quasi-BIC resonances. Then, simultaneous in-plane symmetry breaking was introduced in both the x and y directions to excite two more resonances. The physical mechanisms of these BIC modes were investigated by multipole decomposition of the scattering cross section and electromagnetic near-field analysis, confirming that they are governed by toroidal dipole (TD) modes and magnetic dipole (MD) modes. We also investigated the flexible tunability and evaluated the sensing performance of our proposed metasurface. Our work is promising for different applications requiring stable and tunable resonances, such as optical switching and biomolecule sensing.

Polarization converters are essential components of optical systems. Here we propose an all-dielectric metasurface linear-polarization converter composed of silicon diatomic nanopillar arrays. The two nanopillars are identical except for the azimuthal angle. The converter can orient the linear polarization to arbitrary angles by changing the two orientation angles of the nanopillars. And the polarization conversion efficiency remains above 90%. The mentioned metasurface is analyzed theoretically and demonstrated by numerical simulation. The results show that the polarization angle of the output wave is exactly equal to the sum of two orientation angles. Thus, the polarization angle of the output wave can be easily controlled. The proposed metasurface breaks the limitation of traditional line polarization converters and may have broad application prospects in wireless communications, imaging systems, and other fields.

Localized optical resonances in silicon nanostructures have been increasingly used in color printing. By changing the geometric parameters of the silicon nanostructures to obtain different structural colors, it is possible to get a larger coverage range than the sRGB color gamut in the CIE color space, and achieve ultra-high-resolution color printing. However, the design of specific colors involves iterative optimization of geometric parameters, which is computationally expensive. Thus, it is very challenging to obtain millions of different colors in the color space. In this paper, we trained a feature-crossed neural network with attention mechanism to predict the structural color produced by random silicon nano truncated cones with high accuracy. On the problem of inverse design, we improve the loss function of the tandem network, which solves the non-uniqueness problem in the inverse design process and avoids the tandem net from falling into the wrong solution space. Our model can accurately predict millions of different color points in the CIE color gamut. In addition, the proposed methods can be easily extended to solve the optimization design problems in the field of nanophotonics.

The bound state in the continuum (BIC) has drawn much attention in electromagnetics due to its infinite lifetime and quality factor. By the method of breaking the symmetry in the metasurface, the optically invisible BIC can be converted into visible quasi-BIC with ultra-high quality factor. However, symmetry-breaking metasurfaces often suffer from polarization sensitivity due to structural or field asymmetry. In this paper, we propose a metasurface consisting of nanodisk tetramer clusters to realize the transformation from BICs to quasi-BICs and support four resonances in the near-infrared range. The in-plane center square defect is introduced to provide symmetry-breaking while C4v symmetry is maintained. By performing the multipole decomposition and near-field analysis, these four modes can be demonstrated to be excited by electric quadrupole (EQ), magnetic quadrupole (MQ), magnetic dipole (MD) and toroidal dipole (TD) moments. We demonstrate the full angles polarization-independent characteristic of the metasurface and investigate the robustness by introducing off-center square defects. In addition, we also evaluate the sensing performance of the metasurface as a refractive index sensor. We believe that this work could provide new references for the polarization insensitive metasurface with multiple resonances and help to develop the applications such as biochemical sensing, low-threshold lasing and nonlinear devices.

Full width at half maximum (FWHM) is an important factor affecting the performance of the sensor. In order to improve the quality factor of the surface plasmon resonance sensor, a grating-assisted ultra-narrow band multispectral plasmon resonance sensor structure is proposed in this paper. The structure is composed of periodically alternating SiO2 and Au rectangular nanorods and is placed on the SiO2/Al2O3 thin film layer. The full vector finite element method is used to simulate the optical transmission and sensing characteristics, and the effects of structural parameters and polarization state of incident light on FWHM and sensing characteristics are analyzed. The simulation results show that in the wavelength range of 800-1100 nm, there are two dips formed by plasma resonance and dielectric grating in the transmission spectrum of the structure. The corresponding FWHM can reach 0. 35 nm and 0. 59 nm, respectively. The refractive index sensitivity is 525. 7 nm /RIU and 475. 7 nm /RIU, respectively. The figure of merit is 1502. 00 RIU-1 and 806. 27 RIU-1, respectively, which had potential applications in biological detection, drug screening, membrane biology and other fields.

We propose a broadband tunable and high-efficiency terahertz equal-power beam splitter based on a graphene aperture metasurface. It is composed of multi-sheets graphene with trapezoidal apertures. In a supercell, the graphene sheet contains two trapezoidal apertures etched in a mirror image along the horizontal direction, which are of the same size with opposite phase gradients. We study the operating characteristics of the beam splitter at the graphene Fermi level of 1.0 eV. When the y-polarized plane light is incident vertically, the maximum conversion efficiency is 97.6% at about 8.0 THz, and the reflection deflection angles are ±31°. In addition, in the frequency range from 7.8 THz to 8.6 THz, the efficiency of the beam splitter always remains above 90%. Especially, we adjust the response frequency range of the beam splitter by changing the Fermi level of graphene, which is possible to consistently maintain conversion efficiencies of more than 90% in the broadband range from 6.3 THz to 8.6 THz. Graphene metasurfaces have promising potential for applications in tunable, ultra-thin and integrated terahertz microdevices. Our work provides a possibility to manipulate the electromagnetic waves in this band. We expect that the designed structure will be instructive for the study of terahertz devices.

Metasurfaces with both multifunctionality and tunability hold great application potential in next-generation optical devices. In this paper, we propose a stretchable metasurface composed of arrays of identical dielectric rectangular resonators embedded in the polydimethylsiloxane (PDMS) substrate. It is shown that the metasurface possesses three functions at the operating wavelength of 532 nm. The switching of functions can be implemented by changing the period Px of the metasurface, induced by stretching the PDMS substrate along the x-direction. When the period Px is less than the operating wavelength of 532 nm, the behavior of metasurface can switch between transmissive window and reflective mirror. When the period Px of the metasurface varies from 532 nm to 700 nm, the metasurface act as a dynamic equal-power beam splitter with conversion efficiency higher than 90%, and the corresponding splitting angle can be adjusted from 90° to around 49.5°. Moreover, we achieve the switching of transmissive window/reflective mirror/split-ratio-variable splitter based on the metasurface consisting of arrays of identical L-shaped resonators embedded in the PDMS substrate.

Smart windows can moderate the transmission and absorption of sunlight according to seasonal changes and personal preferences. Here, we designed a multilayer thin-film structure of an electrochromic smart window that can effectively regulate the transmission and absorption by rotating the sample and adjusting the bias voltage. This lithography-free, polarization-independent, incident angle-insensitive structure with an extensive modulation transmission range improves new ideas for the future development of electrochromic windows.

Chalcogenide compound Ge2Sb2Se4Te1 (GSST), an emerging phase change material, features drastic optical property contrast between the amorphous and crystalline states. In this paper, a compact and nonvolatile polarization-rotating optical switch is proposed and demonstrated numerically assisted by a L-shaped GSST waveguide, covering the telecom C- band. The switch exhibits greatly competitive performances with a good trade-off for a low insertion loss below 0.33 dB, a high switching depth (SD) above 34.2 dB, a compact device footprint (length = 4.28 mu m) and an operating bandwidth over 100 nm. The device performances with the intermediate states between amorphous and crystalline of GSST are investigated as well. Furthermore, the results show that the optical switch exhibits a satisfactory robustness with SD > 33.8 dB within the +/- 20-nm variations for both etching width and height. This work can provide a viable scheme to achieve the functionality of combining polarization rotation and switching, which will simplify the system architecture and improve the integration of polarization diversity circuits for optical routing on chip.

针对现阶段表面等离子体激元(SPP)传感器存在灵敏度低、结构制造复杂等问题,提出了一种由金属-绝缘体-金属波导和嵌入银纳米棒的谐振腔构成的高灵敏度、可调谐的SPP传感器.采用时域有限差分法对所设计传感器的光传输特性及传感特性进行了理论研究.仿真结果表明:当谐振腔引入或者不引入银纳米棒时,传输谱在500～3500 nm波长范围会呈现4个或者2个谐振峰;该结构的折射率灵敏度高达2116.72 nm/RIU,品质因数为27.503;通过对谐振腔填充乙醇,该结构可实现对环境温度的测量,温度灵敏度可达0.982 nm/℃.

The absorber based on planar metal/dielectric thin films has attracted much attention due to its superior absorption performance, simple preparation process and broad application prospects. In order to improve the absorption performance, an ultra-broadband perfect absorber with a multilayered Zr/SiO2 structure is proposed, which is based on multiple Fabry-Perot (FP) resonant absorption. The structural parameters arc optimized by employing the transfer matrix method combined with the genetic algorithm and the calculation results show that as for an absorber with a 10-layered Zr/SiO2 structure (which constitutes 1 series FP cavities), the minimum absorption efficiency exceeds 96.6% and the average absorption efficiency is up to 98.6% in the wavelength range of 0.1-3.0 mu m. Even as for one with only a 4-layered structure, its average absorption efficiency still reaches 91.5%. Furthermore, the absorption characteristics of the proposed structure arc analyzed in other wavelength ranges and the relation of its average absorption efficiency with lay number is also calculated. Compared with other absorbers with complex structures, the proposed absorber has the characteristics of large working bandwidth, high absorption efficiency and simple structure. It has wide application prospects in the fields of solar energy collection, heat radiator, and infrared cloaking.

We numerically demonstrate an ultra-broadband plasmonic absorber by applying chromium and titanium in a 3D metamaterial structure. One unit cell of the proposed absorber consists of continuous Cr/SiO2 multi-layers covered by two Ti nanodisks for exciting multiple magnetic dipole resonances and localized surface plasmon resonance. The optical simulation results show that the average absorption of the plasmonic structure exceeds 98.4% in the wavelength range of 400- % in the wavelength range of 400−4000 nm. The broadband and high absorption benefits from impedance matching between the nanodisks array and the free space in the wavelength range. Through thermal simulation, we also investigated the photothermal heating generation in the plasmonic metamaterial structure. The temperature rise in the proposed structure is approximately 447 K with an incident wavelength of 618 nm and a light flux of 100 W/cm2. Due to the ultra-broadband absorbing performance, the presented design has possibilities in the fields of photodetector applications, solar energy harvesting, thermal emitters, and infrared cloaking.