Unidirectional scattering plays an essential role in controlling light-matter interactions and supports a wide range of applications, including optical sensing, nanoantennas, and biomedical imaging. However, achieving high-intensity, customized unidirectional scattering in a single subwavelength nanoparticle governed by electric modes remains a significant challenge. We propose a classification-assisted transformer-based deep neural network, termed CSSformer, for the intelligent design of strong unidirectional scattering driven solely by electric modes in four-layer core-shell structures (CSSs). By employing a spectrum-splitting scheme, CSSformer overcomes the severe dimensional mismatch between input and output vectors, significantly outperforming traditional multilayer perceptron (MLP) in both forward prediction and inverse design. Furthermore, to simultaneously ensure high directionality and strong scattering intensity, both unidirectional and total scattering spectra are taken into account during the inverse training process, while a classification module is embedded to enable efficient learning across multiple distinct CSS configurations. An on-demand spectral pre-design strategy is introduced, allowing users to define arbitrary spectral features for real-time, tailored design of strong directional scattering. This study provides an efficient deep-learning framework for manipulating scattering directionality, with promising implications for photovoltaics, antenna design, and optical sensing.

Light amplification in photonic time crystals (PTCs), enabled by their momentum bandgap, is a well-established phenomenon. However, prior research has predominantly focused on achieving a substantial gap, whereas the controlled manipulation of light properties remains largely unexplored. Here, we exploit spatially finite magneto-optic photonic time crystals (MO-PTCs) to achieve polarization- and frequency-selective light amplification. By magnetizing the MO-PTC, we dynamically tune the effective permittivity of extraordinary light (e-light), thereby controlling its amplification threshold. Applying periodic modulation to the diagonal elements of the dielectric tensor enables selective amplification of either ordinary light (o-light) or extraordinary light, depending on which has the lower threshold. Furthermore, modulating the off-diagonal elements induces an effective modulation comprising both the fundamental frequency and its second harmonic in the extraordinary light. Adjusting the extraordinary light's permittivity allows preferential amplification of either the fundamental or second-harmonic component based on their respective thresholds. This work advances the understanding of spatially finite PTCs and introduces a novel approach to light manipulation in time-varying media.

C-points in momentum space correspond to circularly polarized states, with broad applications in light–matter interactions, chiral lasing, and nonlinear optics. However, achieving a circularly polarized state at the Γ point requires relocating C-points to this position, which necessitates breaking both in-plane and out-of-plane symmetries. Besides, the chiral responses are typically confined to a narrow range of incident angles. Here, by including periodic groove perturbations on both sides of the grating slit, guided-mode resonances (GMRs) with a high quality factor (∼10 5 ) that propagate parallel to the grating slit are created, which possess two pairs of C-points off the Γ point. By adjusting the spacing between the grooves on both sides of the grating slits, one pair of C-points with the same handedness gradually evolves toward the Γ point and is eventually located on a high-symmetry axis, resulting in near-circularly polarized states over an extended momentum range along that axis, while preserving the in-plane C 2 -symmetry. Furthermore, we achieve spectrally tunable field-enhanced circular dichroism (CD) as well as nonlinear CD exceeding 50 dB. The proposed structure also exhibits strong robustness against fabrication imperfections, offering practical feasibility for chiral photonic applications.

Mode-coupling is an important method for enhancing the quality (Q) factors of guided mode resonances (GMRs) in photonic crystal slabs. In square lattices, GMRs inherently exhibit orthogonality and degeneracy due to C4 symmetry, with different orders of GMRs typically displaying distinct frequencies at the Γ point. Here, we propose a versatile and highly effective approach to achieve ultrahigh Q GMRs in rectangular lattices by exploiting spatial degrees of freedom. Specifically, two distinct types of GMRs, supported by orthogonally oriented propagation directions, can robustly couple to form a hybridized GMR with an exceptionally ultrahigh Q value. Our theoretical analysis indicates that the formation of such hybridized GMRs requires merely the design of an appropriate period, based on the dispersion relations of the guided modes, obviating the need for complex structural modifications. This research offers a practical and innovative method for realizing ultrahigh Q GMRs in photonic crystal slabs, thereby providing more possibilities for light-matter interactions, nonlinear optics, and optoelectronic device applications.

A novel design of a spherical hyperbolic metamaterial (HMM) cavity aimed at enhancing color-transparent displays is proposed. This HMM cavity consists of a silver core wrapped by several stacks of alternating layers of dielectric and silver. Based on effective medium theory and Mie scattering theory, we demonstrate that such HMM cavity supports multiple whispering-gallery modes with deep subwavelength characteristics. The number of whispering-gallery modes with the same angular momentum is equal to the number of silver layers within the HMM cavity. Furthermore, we demonstrate that these excited whispering-gallery modes are capable of strongly confining the electric fields within different dielectric shell layers, resulting in reduced Ohmic losses and narrow resonance linewidths. In addition, we systematically investigate how the structure parameters affect whispering-gallery modes for a HMM cavity with 5 alternating layers of dielectric and silver. Interestingly, by increasing the thicknesses of most outer dielectric and silver layers, it is observed that the resonance wavelengths of TM1,2 and TM1,3 modes remain nearly unchanged. However, the TM1,1 mode experiences a significant blueshift, and the intensity of the TM1,1, TM1,2 and TM1,3 modes can be substantially tuned. Consequently, through structural optimization, the HMM cavity can support triple narrowband resonances in the red, green, and blue spectral regions. Finally, we show that the HMM cavity exhibits dipole radiation characteristics at the three resonance wavelengths, effectively confining light within an angular range spanning from -45° to +45° relative to the incident light direction, and confirming the scattered light viewed from a wide angle. These features of the HMM cavity make it suitable for achieving high transparency, brightness, and wide viewing angles in full-color transparent displays.

Structural coloration generates some of the most vibrant colors in nature and has numerous applications. Inspired by the recently reported transparent displays relying on wavelength-selective scattering, we address the novel problem of transparent structural color, which requires nanoparticles to have a narrow-band and broad-angle scattering response. Although superscattering beyond the single-channel limit has important prospects for enhancing transparent displays, it has not yet been reported. Here, we propose a simple dielectric-gold core-shell nanoparticle capable of superscattering at blue (lambda = 450 nm) and green (lambda = 532 nm) wavelengths, along with a dipolar surface plasmon resonance (SPR) at the red wavelength (lambda = 640 nm), making it suitable for full-color transparent displays. We demonstrate that the superscattering at lambda = 450 nm arises from the overlap of the epsilon-near-zero (ENZ) dipolar and quadrupolar modes. Furthermore, the coupling of conventional quadrupolar and dipolar modes can also enhance the scattering efficiency at lambda = 532 nm, breaking the single-channel limit. Lastly, we show that the optimized nanoparticles can confine the scattering light within the forward hemisphere at lambda = 450 nm and 532 nm, due to the interaction of quadrupolar and dipolar modes. Additionally, they exhibit dipole far-field radiation characteristics at lambda = 640 nm with a wide angular beamwidth > 60 degrees. The simple structural nature and unique scattering properties of proposed dielectric-gold core-shell nanoparticles hold promise applications in full-color transparent displays, spectroscopy, and biomedical imaging.

The widespread use of light emitting diode (LED) based devices makes us inevitably exposed to a blue-enriched environment and brings a potential risk to our eyes. Developing a blue-light-blocking filter with narrow absorbing band, so as to only block harmful blue light (415–455 nm) is highly expected. Here, we create a blue-light-blocking film, consisting of a transparent medium embedded with plasmonic nanoparticles (NPs) that selectively absorb harmful blue light. We present the optimal design based on Mie theory by comprehensive scanning of the parametric space for the NPs, and experimentally demonstrate this concept with a blue-light-blocking film made of silver NPs in a polymer matrix by a simple solvothermal method. For the case of the silver NPs content ∼0.16 wt%, the film can block harmful blue light ∼65% at λ 0 ≈ 430 nm, while maintaining high transparency for the long wavelength light ( λ 0 > 500 nm). We also demonstrate that it is possible to correct color cast by optimizing the design of the plasmonic NPs with sharp absorption resonances at yellow waveband. This method has attractive features including simplicity, low cost, non-toxic and scalability to large sizes, which makes it beneficial for blue-light-blocking applications.

We report a transparent display based on a metasurface of silver nanoparticles (Ag NPs), consisting of a transparent substrate and a layer of Ag NPs deposited by a dielectric film. The Ag NPs metasurface is prepared by a simple and direct annealing process. It presents a deep transmission valley at the wavelength ofλ= 468 nm and enables desired transparent display by projecting the monochromatic image onto the metasurface. We also demonstrate that the formed Ag NPs can be approximated as truncated nanospheres, which have obvious directional scattering properties, and can radiate most of the scattered energy into the backward hemisphere with a relatively large angular beamwidth (the full width at half maximum of the scattered intensity) of ∼90°. Therefore, the fabricated displays possess wide viewing angles and high brightness characteristics. Additionally, the transmission modes can be red-shifted to the wavelength ofλ= 527 nm by controlling the thickness of the deposited dielectric film. This approach using traditional thin film deposition and moderate annealing processing techniques enables simple, low-cost, and scalable fabrication in large areas for transparent displays.

提出一种基于银纳米颗粒等离激元共振和耦合效应的彩色透明显示屏.对银颗粒优化设计,说明在红、绿、蓝三波段能够出现三个散射峰,可用于增强彩色显示性能;接下来,通过溶液热法制备出该屏幕;经投影仪对屏投影测试发现确实具有彩色、高透、高亮和宽视角.另外,研究发现在等离激元共振及耦合作用下,银颗粒在红、绿、蓝三个共振位置均具有偶极子的远场散射形貌,充分解释了显示屏高亮和宽视角的原因.提出的透明显示屏具有透明度和亮度高、观察视角宽、制备工艺简单、成本低等特点,在透明显示领域将有大的应用潜力.

A novel spherical hyperbolic metamaterial (HMM) cavity for enhancing color-transparent display is designed in this work. This HMM cavity consists of a silver core wrapped alternatively by several dielectric layers and silver layers. According to the effective medium theory and Mie scattering theory, we demonstrate that such an HMM cavity supports multiple whispering-gallery modes with deep subwavelength characteristics. The number of whispering-gallery modes with the same angular momentum is equal to the number of silver layers within the HMM cavity. Furthermore, we demonstrate that these excited whispering-gallery modes are capable of strongly confining the electric fields within the different dielectric shell layers, thus reducing Ohmic losses and narrowing resonance linewidths. In addition, we systematically investigate how the structure parameters affect whispering-gallery modes for an HMM cavity with 5 alternative dielectric layers and silver layers. Interestingly, by increasing the thickness of outermost dielectric layer and silver layer, the resonance wavelength of TM1,2 mode and TM1,3 mode remain nearly unchanged. However, the TM1,1 mode experiences a significant blueshift, and the intensity of the TM1,1, TM1,2 and TM1,3 mode can be substantially tuned. Consequently, through structural optimization, the HMM cavity can support triple narrowband resonances in the red, green, and blue spectral regions. Finally, we show that the HMM cavity exhibits dipole radiation characteristics at the three resonance wavelengths, effectively confining light within an angular range from –45° to +45° relative to the incident light direction, and confirming the scattered light viewed from a wide angle. These features make the HMM cavity suitable for achieving high transparency, brightness, and wide viewing angles in full-color transparent displays.

We theoretically propose a novel nanolaser based on whispering-gallery resonances (WGRs) in spherical cavities with hyperbolic dispersion, composed of a dielectric core alternately wrapped by graphene and dielectric layers. First, we showed that the multilayer graphene-dielectric core-shell cavities have a negative dielectric constant in at least one direction and exhibit an unusual hyperbolic dispersion. Such cavities can support the whispering-gallery modes with resonance wavelengths much larger than the cavity sizes and can strongly confine the electromagnetic fields in deep subwavelength regions. Moreover, multiple dipole WGR modes with different orders can be excited by such cavities, accompanied by high Purcell factors and strong confinement electric fields within different dielectric layers. Therefore, by introducing gain into these different dielectric layers, lasing at different resonance wavelengths can be realized with a low lasing threshold. For the cavity with a diameter of 404 nm, the lasing threshold at a wavelength of 32.3 mu m is only 80.6 cm(-1). Furthermore, we demonstrated that by manipulating the refractive index of the dielectric layers, graphene Fermi energy, or the number of pairs of graphene and dielectric layers, the lasing wavelengths in a wide spectral range could be easily adjusted. Finally, even for the relatively simple core-shell cavity with only two pairs of graphene and dielectric layers, the ratio of resonant wavelength and cavity diameter for the TM1,1 mode is approximately 50, and the lasing threshold is only 90.74 cm(-1). This type of nanolasers has the characteristics of deep subwavelength, low threshold, and wide-band tunability. Hence, these lasers have great potential for applications in integrated terahertz devices.

本文基于Mie散射理论,设计了三种(Au,Au-介质,介质-Au)球形纳米结构,并研究结构参数及周围环境对结构的光散射性质的影响.说明结构外半径的增加会使共振位置发生红移,线宽增加,并且偶极近似不再成立.经研究发现,在偶极近似下,Au-介质纳米核壳结构中核半径的增大使得散射峰增强,线宽也比金球颗粒的小.并且介质折射率的增加,会使散射峰进一步增强,并产生一定的红移.对于介质-Au纳米核壳结构,当Au层厚度较小的情况下,球模和腔模之间的强耦合作用使得共振峰位置发生较大的红移,散射峰也显著增强.并且随着介质核的折射率增加,会进一步使得模式发生红移.考虑到实际应用,最后通过在Au-介质纳米核壳结构的介质层引入增益,或者减小介质-Au纳米核壳结构半径,发现其均能在石英环境中实现可见光波段的窄带强散射.这些研究结果将对高性能透明显示屏的制备提供重要的理论依据.

We theoretically investigate the light control performances of metal−low-permittivity (LP)−high-permittivity (HP) core–shell nanoparticles (M-LP-HP CSNPs). We demonstrate that a free-standing M-LP-HP CSNP can simultaneously possess the zero-backward (ZB) and near-zero-forward (NZF) scattering at different wavelength ranges due to the interference of electric and magnetic modes. We show that at the wavelength of the ZB and NZF scattering, the ability of CSNPs to confine the optical fields within the cavity is quite robust against the existence of LP substrates. As a result, such unidirectional scattering properties are well maintained when the CSNP is placed on the LP substrate. Furthermore, we demonstrate that in the arrays of CSNPs, the high reflection and transmission can be achieved near the wavelengths of NZF and ZB scattering. Particularly for the case of the optimal inter-particle distance, the reflectance can reach 98% over a wavelength range from 868 nm to 935 nm. These features are further tuned to other wavelengths by varying the structural parameters of the CSNPs.