Shi-Tong Xu

Recently, vector beams with space-variant polarizations have attracted significant attention due to their wide range of applications, among which focal engineering stands out as one of the most representative and important applications. Here, we achieve flexible focal engineering based on the hybridly polarized vector vortex beam. The energy distribution can be manipulated, and the precise control of the tightly focused fields with various shapes at an extremely small scale holds significant application values in various fields such as optical machining, super-resolution imaging, and optical trapping. Moreover, the flexible transverse energy flow is also achieved, which is different from the longitudinal energy flow calculated by Poynting vector from the conventional uniform beam. The particles can be transported along certain paths or to fixed locations, indicating flexible applications in the area of optical manipulating and transporting. This work is of importance and value, as it provides a novel light source and enables various applications in the field of focal engineering.

Quasi-bound states in the continuum (quasi-BICs) supported by metasurfaces play a pivotal role in high-performance optical sensing, owing to their ultrahigh quality factors that significantly boost light–matter interactions with target analytes. Distinct from conventional symmetry-breaking approaches for BIC to quasi-BIC transitions relying on single structures, we investigate dimer metasurfaces based on Babinet complementary metasurfaces (BCMs). Via multipole decomposition and field distribution analysis, we reveal that the multipole decomposition components of the quasi-BICs resonant modes in BCMs are essentially identical, with magnetic dipoles dominating the resonant response, which provides critical theoretical guidance for quasi-BICs design. Furthermore, we demonstrate the sensing performance of the developed metasurface by investigating transmittance spectra under varying arginine concentrations. Notably, the transmittance at the quasi-BICs resonance exhibits a significant variation, whereas the corresponding frequency shift is negligible. This work lays a theoretical basis for quasi-BICs evolution in BCMs and promotes high-performance metasurfaces for sensing.

Self-accelerating beams have consistently been a focus of research, owing to their outstanding properties and wide range of applications. Here, we present a practical beam-synthesis strategy to achieve the self-accelerating arrayed Gaussian beam (AGB). We design the beam using a ‘beam array + phase modulation’ scheme, which is different from most of the existing engineered accelerating beams. We generate the beam experimentally with a 4f system and a spatial light modulator. Numerical and experimental results demonstrate that the propagation trajectory exhibits an obvious transverse deflection, and the main-lobe deflection distance grows with the increasing aperture angle Δ θ . The transverse deflection distance reaches 0.342 mm at z = 30 cm for Δ θ = π / 2 , which is superior to the classic Airy beam in similar configuration. Moreover, the beam possesses good self-healing capability after partial obstruction, with the optimal self-healing performance achieved at an aperture angle Δ θ of π / 2 . These controllable self-accelerating and self-healing properties make the AGB attractive for applications such as optical manipulation along curved trajectories and obstacle-resilient optical communication.

Metasurface-based quasi-bound states in the continuum (quasi-BIC) have emerged as a powerful platform for high-performance optical sensing, owing to their ultra-high quality (Q) factors that greatly strengthen light-analyte interactions. Conventional quasi-BIC excitation schemes primarily rely on symmetry breaking of individual resonant unit cells, which inherently constrain structural design and performance modulation. To address this constraint, this work proposes what we believe to be a novel terahertz (THz) metasurface architecture constructed with H-shaped dimer resonators on a flexible polyimide (PI) substrate. By introducing the asymmetric parameter between two closely spaced subwavelength resonators, the transitions from BIC to quasi-BIC are experimentally realized. Combined with the multipole decomposition and near-field analysis, it is revealed that the generation of quasi-BIC mode in H-shaped dimer metasurface is dominated by electric quadrupole (EQ) modes. As a proof of concept, we perform biosensing experiments using bovine serum albumin (BSA) as a model analyte. The results reveal that the quasi-BIC resonance exhibits observable emergence and disappearance with increasing BSA concentration. This work provides theoretical and experimental support for the development of flexible THz quasi-BIC devices and presents promising application prospects in the field of THz biodetection.

A Fizeau interferometer exhibits high robustness, good stability, and polarization independence. However, when employed for micro-displacement detection, its sensitivity decays with the increase of cavity length. Here, we propose a dispersion turning point (DTP) enhanced Fizeau interferometer to improve the sensitivity. A piece of quartz plate is used as a beam splitter. The DTP is obtained by adjusting the length of the cavity between the reflective coating of the beam splitter and the test surface. When working near the DTP, ultra-high sensitivity to the micro-displacement is realized. In addition, when the working point deviates from DTP, we utilize the zero-dispersion point of quartz to improve the attenuation of sensitivity. A high constant sensitivity of 0.333 nm/nm is achieved within a wavelength range of 56 nm. By tuning the position of DTP, this Fizeau interferometer also possesses another advantage of adjustable dynamic range.

We present a y -shaped metasurface structure integrated with dual U-shaped rings. This structure can excite two resonance modes under linearly polarized wave incidence at 0.28 and 0.49 THz, meanwhile the x -and y -polarized AT values reach up to 0.73 and 0.62 at the two resonant frequencies, respectively. As we know, the linearly polarized wave is a degenerate mode and it can be decomposed into LCP and RCP components with equal amplitude and opposite helicity. Herein, when the incident wave is LCP and RCP, the above two resonance modes undergo degeneracy breaking around 0.28 and 0.49 THz, ultimately forming the independent resonances at 0.26 (0.46) and 0.31 (0.50) THz for RCP and LCP, respectively. As a result, quad-band CD effects achieved at the four resonant frequencies, with values of 0.49, 0.46, 0.56 and 0.64, respectively. Dynamic modulation of the amplitude and frequency response of both AT and CD effects are enabled by adjusting the Fermi energy level of the graphene. This design provides a novel approach for developing multifunctional tunable chiral devices, with potential applications in terahertz communications, biosensing, and polarization control technologies.

In recent years, optical needle in the focal plane, featuring an ultra-long depth of focus and no diffraction confinement over a distance along the propagation direction, has emerged as a hot research topic. In this paper, we propose a structured light beam called the generalized sinc beam (GSB). The beam enables the achievement of ultra-long optical needles through two distinct schemes: self-focusing scheme and tight-focusing scheme, respectively. The self-focusing process capitalizes on the inherent propagation characteristics of the beam, allowing it to naturally converge over an extended distance without substantial divergence, thus forming an ultra-long optical needle. Based on the abruptly self-focusing GSB, the optical needle can reach up to a length of 2.51 × 10⁵λ with λ = 532 nm being the wavelength. Meanwhile, when the GSB is tightly focused, the ultra-long optical needles are achieved, and the needle’s length can reach up to 100λ. The optical needles produced by the GSBs are not only ultra-long but also flexibly controllable, which have broad application potential in various areas such as optical trapping, optical microscopy, atom optical experiments, photolithography, and so on.