Slow light can enhance light-matter interaction and enable compact buffers, delay lines, and high-capacity signal processing. Plasmon-induced transparency (PIT) metasurfaces are an effective platform for such devices, but their design still relies on complex full-wave simulations to explore the nonlinear mapping between geometry and spectrum. We propose a physics-informed deep-learning framework for efficient and interpretable design of PIT metasurfaces for terahertz slow light. In the forward task, an adaptive loss-weighting strategy balances data fitting and physics constraints, where the physical constraints are based on coupled-mode theory (CMT). The validation loss of the model after training reaches 7.9 & times; 10-2 and this model shows better generalization than purely data-driven or fixed-weight models. For inverse design, a Kolmogorov-Arnold network (KAN) is cascaded with the frozen forward model and trained in a self-supervised end-to-end framework using only spectral reconstruction error. This inverse branch achieves a loss of 3.9 & times; 10-3, one to two orders of magnitude lower than a comparable multilayer perceptron. It reduces design time from hours to seconds and effectively mitigates the one-to-many spectrum-to-structure ambiguity. We numerically demonstrate multi-wavelength delay lines, a high delay-bandwidth-product optical buffer (group index approximate to 1.4 & times; 103, delay-bandwidth product approximate to 33.2), and broadband pulse delay, showing that the proposed framework is a general route to physics-informed design of PIT metasurfaces and related nanophotonic devices.

The limited infrared nonlinear optical response of wide-bandgap two-dimensional materials remains a major challenge for ultrafast laser modulation. Here, we report a platinum (Pt) modification strategy to engineer the electronic structure and infrared nonlinear optical properties of SnS2 nanosheets. The Pt-modified SnS2 was synthesized via a combined hydrothermal and atomic layer deposition approach, enabling strong near-infrared (NIR) absorption and enhanced light-matter interaction. Density functional theory calculations and experimental results reveal that Pt incorporation narrows the bandgap and induces a Schottky junction, facilitating interfacial charge transfer. As a result, Pt-SnS2 exhibited increased modulation depths, reduced saturation intensities and enhanced nonlinear absorption coefficients at both 1.03  μm and 1.56  μm. When Pt-SnS2 was employed as a saturable absorber, stable mode-locked operation was achieved at 1032.2  nm with a pulse duration of 306.5  ps, while conventional soliton pulses as short as 582  fs at 1567.8  nm. This work highlights interfacial engineering via noble metal modification as an effective route to enhance nonlinear optical response, providing new opportunities for high-performance ultrafast photonic devices.

Coupling two-dimensional materials with plasmonic metals can significantly enhance their intrinsic optical characteristics. This study investigates the surface plasmons of silver-and nitrogen-doped graphene nano-structures, which enable excellent broadband ultrafast optical modulation in the near-infrared band. Nitrogen-doped graphene modified with Ag nanostructures (Ag/NG) exhibited improved saturable absorption characteristics, including lower saturation intensity and higher modulation depth compared to pristine nitrogen-doped graphene. Moreover, the theoretical analysis revealed that the enhanced nonlinear optical absorption response resulted from the synergistic effects of surface plasmon coupling and carrier transfer mechanisms. Ag/NG nanocomposites were fabricated as passive pulsed laser modulators, successfully generating ultrafast soliton mode-locking pulses with high operational stability at 1.04 and 1.55 mu m. This work offers valuable insights into expanding and optimizing the broadband nonlinear optical responses of two-dimensional nanomaterials for developing high-performance ultrafast pulsed laser modulation devices.

The selective extraction of urea from urine under mild conditions is essential for urban wastewater treatment. Here we devise an in situ electrochemical technique that converts urea, a nitrogen-rich waste, into percarbamide, a crystalline peroxide derivative of urea. This process simultaneously facilitates urine treatment and transforms waste into a valuable product. Using modified graphitic carbon-based catalysts, which are engineered with optimized active sites and structures, the system solidifies hydrogen peroxide and accelerates urea conversion. Precise control of temperature and urea concentration further enhances catalytic performance. The optimized process achieves near 100 The extraction of urea is an important part of wastewater purification and a potential source of valuable fixed nitrogen. Here the authors combine electrocatalytic oxygen reduction with precipitation of urea from urine in the form of a solid peroxide (percarbamide) and demonstrate several potential applications.

MXenes have recently garnered tremendous interest as emerging optoelectronic device materials due to their remarkable optical and electronic properties. However, the uncontrollable nature of surface termination seriously hinders the development of MXenes. Therefore, surface functionalization of MXenes is crucial to optimize their performance. In this study, Ti2C MXene with Br group modification (Ti2CBr2) was synthesized, and its nonlinear optical properties for near-infrared (NIR) ultrafast photonic applications were investigated. Theoretically, first-principles calculations revealed the optical and electronic properties of bare Ti2C and Ti2CT2 (T = -Br, -Cl, -OH, -F, and -O). The results showed that Ti2CBr2 exhibited a superior optical response in the NIR band compared to the other termination adsorptions. Experimentally, Ti2CBr2 displayed large modulation depths of 48.25 % at 1 mu m and 26.36 % at 1.5 mu m, confirming its outstanding saturable absorption properties than many common nanomaterials. Furthermore, stable NIR mode-locking operation utilizing the Ti2CBr2 SA was achieved at 1030 nm and 1563 nm, respectively. This work not only demonstrates the significant promise of Ti2CBr2 in the field of ultrafast photonics but emphasizes the importance of surface functionalization modulation of MXene.

In this study, we propose a novel all-dielectric metasurface polarization converter to realize interconversion of linear and circular polarization in inter-satellite laser communication systems, which function as a quarter-wave plate (QWP). The metasurface exhibits a high transmittance (> 0.8) over the 1500-1600 nm wavelength range, with a peak value exceeding 0.9 at 1550 nm. Additionally, the reflectance is maintained below 0.1 throughout this spectral region. It efficiently transforms y-polarized light into left-handed circularly polarized (LCP) light with an ellipticity exceeding 0.99 and converts right-handed circularly polarized (RCP) light into x-polarized light with a linear polarization degree approaching unity, thereby achieving near-perfect polarization conversion efficiency. Furthermore, we investigate the effects of structural parameters, polarization, and incidence angle on the polarization conversion performance of the metasurface. The results demonstrate that the proposed all-dielectric metasurface achieves dual functionality: efficient interconversion between linear and circular polarization states, while simultaneously enhancing laser communication system efficiency through effective stray light suppression. These results suggest broad applicability of the all-dielectric metasurface in advancing inter-satellite laser communication technologies.

The pursuit of high-performance saturable absorbers (SAs) demands synergistic optimization of modulation depth, saturation intensity, and response speed─a challenge persisting in ultrafast photonics. While two-dimensional (2D) MXenes exhibit great potential as SA candidates, their intrinsic limitations, including weak surface plasmon resonance (SPR) and insufficient near-infrared nonlinear optical responses, hinder further practical laser applications. Herein, guided by the plasmonic coupling theory, we proposed a Ti3C2Tx/Au nanoparticle (T/A) nanocomposite synthesized via a facile ultrasonic-assisted strategy. By engineering size-controlled Au nanoparticles onto Ti3C2Tx MXene surfaces, we constructed T/A-tapered fiber (T/A-TF) SA devices to synergistically amplify light-matter interactions. Nonlinear transmission measurements demonstrated that the T/A nanocomposites exhibit significantly enhanced modulation depth alongside markedly reduced saturation intensity at 1.03 and 1.55 μm wavelengths. The improved saturable absorption can be attributed to localized surface plasmon resonance (LSPR) coupling of randomly distributed Au NPs and strong plasmon coupling and electron transfer between Au NPs and Ti3C2Tx, as illustrated by finite element method (FEM) simulations. Based on the exceptional nonlinear saturable absorption properties, the T/A-TF was integrated into ytterbium-doped fiber lasers (YDFL) and erbium-doped fiber lasers (EDFL), generating ultrashort mode-locked pulses of 335 ps (1030.6 nm) and 510 fs (1561.4 nm), respectively. These results demonstrate the critical role of plasmonic coupling in enhancing the optoelectronic performance of MXene-based heterostructures, opening broader avenues for engineering high-efficiency MXene nonlinear photonic devices.

Metasurfaces provide opportunities to enhance nonlinear optical processes. In this paper, we present a nonlinear all-dielectric metasurface with high-quality-factor (high-Q-factor) resonant modes in the vicinity of bound states in a continuum (BICs) to enhance the conversion efficiency of third-harmonic generation (THG). By breaking the symmetry of the metasurface, a quasi-BIC (Q-BIC) with finite lifetimes and large Q factors can be excited and the localized field can be significantly enhanced. Such distinctive-mode engineering yielded a THG conversion efficiency of 3.98% at a pump power of 1 MW/cm2. In addition, compared with previous studies, the THG conversion efficiency, the switch between single and dual modes of can be dynamically tuned by adjusting the asymmetry parameter Delta r, the polarization angle of the incident light, and the height of the silicon nanopillar. The results of this study offer insight into harmonic generation at the nanoscale level.

In this work, we present a high-quality (Q) dual-resonance sensor based on all-dielectric metasurface for refractive index and temperature sensing simultaneously. The all-dielectric metasurface was composed of a periodic array of Si nanocluster placed on the commercially available glass substrate. Two distinct optical resonance modes with extremely high Q factors of 13500 and 14900, a magnetic quadrupole mode (MQ), and toroidal dipole mode (TD), are observed at 1614.12 nm, and 1639.02 nm in the reflection spectra, and confirmed by the electromagnetic field distribution of each resonance. To further reveal the underlying coupling effects of the two resonances, we also perform a systematic analysis of the influence of the differences in radius (Delta R) and gap (Delta x and Delta y). At last, the refractive index and temperature sensing performance were investigated. More specifically, the proposed sensor exhibits a maximum refractive index sensitivity of 418 nm/RIU for the analyte refractive index range between 1.33 and 1.37, and maximum temperature sensitivity of 86.4 pm/degrees C in the range of 0 degrees C-40 degrees C, which demonstrates great linear relationship and is much better than the previous sensors based on all-dielectric structure. The proposed all-dielectric metasurface is an effective way to achieve refractive index and temperature dual-parameter sensing, which will facilitate wide applications in unstable environment, such as the measurement of temperature and salinity in seawater.

An all-dielectric hollow cylinder tetramer metasurface with two high Q resonances is proposed and numerically simulated in the near-infrared band. By researching the electromagnetic field distributions of the resonances at 1310.5 nm and 1359.0 nm, it can be proved that they are original from electric quadrupole (EQ) and magnetic dipole (MD). The Q-factor of the two resonances can be high up to 1024 and 45353, which is much higher than the previous work. The effect of the structural gap size on the resonance is also investigated. In addition, we studied the sensing performance of the metasurface for seawater salinity and temperature measurement, the maximum sensitivity can reach 0.0978 nm/parts per thousand and 30 pm/degrees C, respectively. Salinity and temperature can be precisely identified based on the two sensing signals, so the proposed nanostructure is suitable for simultaneous detection of salinity and temperature in oceanography applications. And more possibilities are provided for developing high-performance sensors for ocean observation.

Recently, volatile solid additives have attracted tremendous interest in the field of organic solar cells (OSCs), which can effectively improve device efficiency without sacrificing the reproducibility and stability of the device. However, the structure of reported solid additives is onefold and its working mechanism needs to be further investigated. Herein, a novel non-halogenated and twisted solid additive 1,4-diphenoxybenzene (DPB) is employed to optimize the morphology of the active layer in OSCs. The properties of additive DPB, morphology of active layer, and carrier dynamics behaviors have been systematically investigated through theoretical calculations, in situ and ex situ spectroscopy, grazing-incidence wide-angle X-ray scattering (GIWAXS), and grazing-incidence small-angle X-ray scattering (GISAXS) measurement, as well as ultrafast spectroscopy technology. The results reveal that the twisted additive DPB selectively interacts with acceptor Y6, and thus forms optimized morphology of active layer with increased molecular crystallinity, tight molecular packing, and favorable phase separation. As a result, the optimized devices deliver a remarkable power conversion efficiency (PCE) of 19.04%, which is the highest value for the D18-Cl:N3 system to date. These results demonstrate that non-halogenated and twisted solid additive DPB has broad prospects in the preparation of highly efficient OSCs, providing theoretical and experimental guidance for the development of high-performance solid additives. In this work, a novel halogen-free and twisted volatile solid additive 1,4-diphenoxybenzene (DPB) has been employed to control the morphology of the active layer in organic solar cells (OSCs). As a result, a champion power conversion efficiency (PCE) of 19.04% has been obtained in D18-Cl:N3 binary OSCs, which is the highest value for the reported D18-Cl:N3 OSCs to date. image

All-dielectric metasurfaces underpinned by the physics of bound states in the continuum (BICs) have surged interest due to their spectral selectivity and strong light confinement. In this work, We propose a compensation mechanism for SP-BIC with stable resonance wavelength and controllable Q-factor. Here we take metasurfaces consisting of four nano-square disks as an example to break the symmetry of the unit cell by both x-compensation and y-compensation, respectively, and the resonance wavelengths are stable. The results show that the four nanodisks are excited in two modes with x-compensation and y-compensation when only C2 symmetry is preserved, and in one mode with x-compensation and y-compensation when only σx symmetry is preserved. Multiple decomposition results show that the loop dipole and magnetic dipole dominate the modes that retain only C2 symmetry excitation. In contrast, the magnetic dipole dominates the mode that retains only the σx symmetry excitation. Both modes excited by the compensation mechanism have stable resonances with high q-factors under the condition of preserving only C2 symmetry or only σx symmetry. Metasurfaces realized by the compensation mechanism may find promising applications in enhanced light-matter interactions such as lasers, sensing, strong coupling, and nonlinear harmonic generation.

Electromagnetic metamaterials are artificial subwavelength composites with periodic structures, which can interact strongly with the incident light to achieve effective control of the light field. Metamaterial absorbers can achieve nearly 100% perfect absorption of incident light at a specific frequency, so they are widely used in sensors, optical switches, communication, and other fields. Based on the development history of metamaterials, this paper discusses the research background and significance of metamaterial perfect absorbers. Some perfect absorption mechanisms, such as impedance matching and coherent perfect absorption, are discussed. According to the functional division, the narrowband, dual frequency, multi-frequency, broadband, and tunable metamaterial perfect absorbers are briefly described.

We propose a dual-pattern broadband polarization converter in the terahertz band using a vanadium dioxide (VO2) and graphene metasurface. The converter can be switched between transmission and reflection patterns by controlling the phase of VO2. In the insulating state of VO2 and with the Fermi energy of graphene (Ef) set to 1 eV, the converter works in transmission mode and can convert linearly polarized waves. In the metallic state of VO2 and with Ef set to = 0 eV, the converter works in reflection mode and can function as a quarter-wave plate. The proposed converter is expected to have applications in integrated devices that control the polarization state of terahertz waves.

A multifunctional metasurface based on graphene and vanadium dioxide (VO2), which can function as a broadband absorber, half-wave plate (HWP), and quarter-wave plate (QWP) in the terahertz frequency band, is designed in this study. When VO2 is in the metal phase, the multifunctional metasurface operated as a broadband absorber in the range of 0.89-2.36 THz. The designed multifunctional metasurface can switch between HWP and QWP by adjusting the Fermi energy of graphene through voltage biasing when VO2 is in the insulated phase. When the Fermi level of graphene is 0 eV, the designed structure acts as an HWP to achieve linear-to-linear (LTL) polarization conversion and preserve the reflection chirality of circular polarization at 0.68-2.64 THz. When Ef = 0.3 eV, the designed structure functions as a QWP in 0.89-2.51 THz to realize the interconversion of linear polarization and circular polarization. Furthermore, the effects of the polarization and incidence angles on the operating performance are discussed. This study demonstrates that the multifunctional metasurface has prom-ising applications in terahertz optical switches, electromagnetic stealth, modulators, and communication systems.

In this numerical study, an all-dielectric metasurface consisting of silicon disks with tilted split gap, which can measure the refractive index and temperature is proposed. It is demonstrated that the double resonances in the near-infrared wavelength are excited by toroidal dipole (TD) resonance in different directions. Further analysis proves that the resonance at the short wavelength corresponds to the TD resonance governed by the symmetryprotected bound state in the continuum (BIC), and it can be transformed to the TD quasi-BIC resonance with a high quality-factor (Q-factor) by breaking symmetry. The spectral responses to different incidence angles are evaluated. The high Q-factor of the TD quasi-BIC makes the designed metasurface a promising sensing candidate; the results show that the sensitivity and figure of merit for refractive index sensing are 746 nm/RIU and 18650 RIU-1, respectively. For temperature sensing, the sensitivity can be as high as 54 pm/degrees C. This study provides a new approach for the excitation of strong TD resonance quasi-BIC, which facilitates the design of highperformance sensing applications.

Curriculum is a primary unit for talents cultivating system and the carrier of establishing morality. Basing on the platform of national first-class undergraduate for applied physics major, national experimental teaching demonstration center for applied physics major and key teaching and research projects of Shandong Province, we persist in student's development as the center and moral education as the fundamental task. We launched exploration and practice around the innovation, profound and challenging of the course, and built a triune talent cultivation system with knowledge, ability and quality. And some initial achievements have been realized. The case of Physical Optics can provide demonstration and promotion for other courses.

专业是人才培养的基本单元.作为首批国家级一流本科专业,青岛大学应用物理学专业在建设过程中瞄准区域经济发展,实施"通识+专业+多元/实践"的人才培养模式,通过聚焦课程思政、构建一流师资队伍、打造一流课程、产教研协同育人等举措,实现了"厚基础、宽口径、重实践、强能力"的理工融合新工科育人特色.为地方区域经济建设培养了大批高素质创新人才.

We propose a temperature-tunable and dual-broadband switchable coherent perfect absorber (CPA) composed of an annulus-disk-shaped InSb pattern and a complementary graphene layer. By controlling the Fermi level of graphene, the temperature of InSb, or the relative phase of incident beams, the working frequency and absorption of the CPA can be continuously adjusted. For a Fermi energy of 0 eV, the dual-band coherent perfect absorptivities exceed 99%. The designed structure achieves broadband absorptance of over 90% in the frequency range of 0.145 THz to 1.24 THz, with a relative bandwidth of about 158.12% for a Fermi energy of 0.5 eV. Moreover, the temperature-dependent permittivity of InSb enables thermal tuning of the dual-band CPA in the THz region. Furthermore, by altering the relative phase of input beams, the absorptivity can be continuously varied between less than 1.2% and more than 90% in the dual-band and broadband modes. Additionally, the designed CPA exhibits insensitivity to the polarization angle within the range of 0 degrees to 90 degrees. Therefore, this multifunctional CPA holds significant potential for applications in modulation, sensing, all-optical switches, and coherent photodetectors.

A polarization-independent, all-optically modulated multiband metamaterial coherent perfect absorber (CPA) is proposed. Numerical simulation results reveal that the absorber can be controlled over a wide range of amplitudes by changing the phase difference of two incident light beams. The all-optical modulation can be extended to telecom wavelengths, allowing for simultaneous modulation of absorption at 1310 nm and 1550 nm. In addition, switchable logical gate states can be achieved at the dip between absorption peaks. The proposed absorber utilizes bound states in the continuum (BIC) mode to realize another absorption band, expanding the application range and enhancing its flexibility. The results suggest that the proposed absorber has a promising modulated optical response, with potential applications in developing optical switches, smart multi-band absorbers, telecom devices and so on.