Tianbao Yu

Enhanced chiral absorption in nanostructures has widespread applications in chiral sensing, photodetection, and polarized imaging. In this work, we theoretically analyze and numerically demonstrate that an all-dielectric planar chiral metasurface enables strong chiral absorption within a transparent band by engineering multipolar Mie resonances into an accidental quasibound state in the continuum (quasi-BIC). The quasi-BIC mode exhibits a sharp π phase shift for one circular polarization while remaining nearly invisible in the transmission spectrum. Upon introducing a small material loss, this mode decouples completely from the orthogonal polarization, yielding near-unity chiral absorption. This work offers new insights into quasi-BIC-assisted chiroptical effects and provides a promising platform for compact chiral photonic devices.

Realizing a planar metasurface with a high quality (Q) factor that simultaneously possesses perfect intrinsic chirality and nonlinear chirality remains a key challenge. Here, through theoretical analysis and full-wave numerical simulations, we propose a high-Q planar silicon metasurface with intrinsic chirality enabled by Brillouin zone folding. Through band engineering, high-Q quasi-guided modes are excited at the Γ point, while breaking the in-plane mirror symmetry enables selective coupling to circularly polarized light. The optimized structure achieves a near-perfect intrinsic chiral response with a Q factor above 2200, a linear circular dichroism (CD) larger than 0.99, and a nonlinear CD exceeding 0.999. Moreover, the Q factor of the chiral quasi-guided mode can be effectively tuned while maintaining near-unity CD. Strong chiral selectivity and a stable high-Q response are preserved over an incidence-angle range of ±2.5°. This work establishes a theoretical framework based on Brillouin zone folding for engineering chiral metasurfaces, providing useful design guidelines for future high-performance chiral photonic and optoelectronic devices.

Conventional spectrometer and polarimeter systems rely on bulky optics, limiting compact integration and hindering multi-dimensional optical sensing capabilities. Here, we propose a spectropolarimeter enabled by metasurface-based diffractive optical networks that simultaneously perform spectrometric and polarimetric measurements in a compact device. By leveraging the wavelength- and polarization-dependent phase modulation of metasurfaces, our system encodes the spectral and polarization information of incident light into spatially resolved intensity distributions, which are decoded by a co-designed deep neural network, enabling simultaneous high-accuracy reconstruction of spectral compositions and Stokes parameters through a single-shot measurement. Experiments validate the method’s accurate reconstruction of the spectral and polarization information across a broad wavelength range and further confirm its imaging capability. Notably, we demonstrate a chip-integrated sensor prototype combining both measurement functionalities into a commercial image sensor. This integrated platform provides a compact solution for on-chip multi-dimensional optical sensing, holding potential for versatile sensing, biomedical diagnosis, and industrial metrology.

Skyrmions are topological defects belonging to nontrivial homotopy classes in particle theory. Their remarkably stable topology has recently been observed in electromagnetic waves. For the evanescent fields near a surface, this has been realized so far only for elementary optical skyrmions, with a fixed skyrmion number. Here we report, both in theory and experiment, the concept of moiré plasmonic skyrmion clusters, where multiskyrmions are nested to form a large optical skyrmion cluster. By leveraging twistronics engineering of plasmonic nanostructures, we demonstrate both periodic and quasi-periodic optical skyrmions, revealing a large degree of topological control. In a misaligned composite nanostructure, the rapid inverting of optical skyrmion number is achieved, which is explained by a lattice model. This topological change of moiré plasmonic skyrmion clusters can serve as a precise beacon of the relative alignment deviation between composite nanostructures.

The Casimir force, an attractive force between two parallel, uncharged, perfectly conducting plates separated by a small gap has attracted much attention not only because it is fascinating phenomenon in quantum electrodynamics, but also because of its important applications in microelectromechanical systems (MEMS). Although the Casimir force is extremely small, it plays a dominant role in MEMS when the distance between device components is also very small. The failure of MEMS due to stiction caused by attractive force motivates the study of repulsive Casimir force. As a result, more and more derivative concepts related to the Casimir force have emerged. Aside from the attractive and repulsive Casimir forces, the lateral Casimir force can occur between sinusoidally corrugated surfaces. Casimir friction arises when two plates are in relative motion even if they are not in direct contact. Such phenomenon not only reveals the non–intuitive nature of the quantum vacuum, but also demonstrate potential applications in nanoscience and quantum technology. In addition, a rotating nanoparticle can also experience a lateral Casimir force when it rotates near a plate, the underlying mechanism is different from that occurring between corrugated surfaces. In particular, when the nanoparticle rotates in the proximity of an optically anisotropic plate, an axial Casimir force along the direction of the rotation axis is exerted on the nanoparticle. At present, these novel phenomena related to the Casimir force form the foundation of Casimir physics research. Here, we focus on the recent progress in the theoretical and experimental research on the Casimir effect including the attractive Casimir force, repulsive Casimir force, lateral Casimir force, and Casimir friction. We also review the applications of various Casimir effects in the field of nanotechnology. The Casimir effect provides new perspectives on MEMS and quantum information processing, and may inspire new experimental approaches and technological applications. This phenomenon holds substantial scientific significance and promising application potential across both fundamental research and engineering fields.

Conventional spectrometer and polarimeter systems rely on bulky optics, fundamentally limiting compact integration and hindering multi-dimensional optical sensing capabilities. Here, we propose a spectropolarimeter enabled by metasurface-based diffractive optical networks that simultaneously performs spectrometric and polarimetric measurements in a compact device. By leveraging the wavelength- and polarization-dependent phase modulation of metasurfaces, our system encodes the spectral and polarization information of incident light into spatially resolved intensity distributions, which are subsequently decoded by a trained deep neural network, enabling simultaneous high-accuracy reconstruction of both spectral compositions and Stokes parameters through a single-shot measurement. Experiments validate the proposed network's accurate reconstruction of the spectral and polarization information across a broad wavelength range, and further confirm its imaging capability. Notably, we demonstrate a chip-integrated sensor prototype combing both measurement functionalities into a commercial CMOS image sensor. This integrated platform provides a compact solution for on-chip multi-dimensional optical sensing, holding significant potential for versatile sensing, biomedical diagnosis, and industrial metrology.

The buried interface plays a vital role in determining the performance and durability of perovskite devices since it influences the charge movement, defects at the interface, and the growth of crystals. However, the self‐assembled monolayer (SAM) generally leads to poor contact due to the weak intermolecular interactions. Here, an effective co‐assembly monolayer method is reported by incorporating acetyl dl‐carnitine chloride (ACL) into [4‐(3,6‐dimethyl‐9H‐carbazol‐9yl) butyl] phosphonic acid (Me‐4PACz) ethanol solution. The application of the ACL improves the coverage of SAM and simultaneously enhances the chemical bonding at the buried interface. As a result, the perovskite solar cells achieve a power conversion efficiency of 25.78% under simulated AM1.5 light conditions, maintaining more than 90% of their original efficiency after ≈600 h of operation at peak power.

Introducing topological lattice defects, such as dislocations, into topological photonic crystals enables the emergence of many interesting phenomena, including robust bound states and fractional charges. Previous studies have primarily focused on the realization of dislocation modes within a single band gap, which limits the number of dislocation modes and their applications. Here, we design a topological photonic crystal with two topologically non-trivial band gaps. By introducing a dislocation defect into this system, we observe the emergence of localized dislocation modes in both band gaps. Furthermore, we demonstrate a two-channel add-drop filter by coupling two dislocation modes with topological edge modes. These findings are rigorously validated through full-wave numerical simulations and experimental pump-probe transmission measurements. Our results provide a foundation for further exploration of dislocation modes and unlock the potential for harnessing other topological defect modes in dual-band-gap systems.

Here, we propose an etchless bismuth iron garnet layer assisted by a one-dimensional resonant grating waveguide to enhance transverse magneto-optical Kerr effect (TMOKE) via the excitation of a quasi-bound state in the continuum. The TMOKE amplitude can be tailored by manipulating the perturbation parameter, and it can reach as high as 1.978, approaching the theoretical maximum value of 2. Additionally, a single-mode temporal coupled-mode theory is employed to further reveal the underlying physical mechanism. It is found that the TMOKE is strongly related to the linewidth of the quasi-bound states in the continuum resonance and local field enhancement, which are pivotal factors in the design and optimization of photonic devices. Our work provides a simple and efficient approach for enhancing TMOKE based on an easy-to-fabricate platform, laying the groundwork for exploring and developing magneto-optical devices such as sensors, magnetic storage devices, and nonreciprocal photonic devices.