Here, we experimentally investigate multiple high-quality quasi-bound states in the continuum (BICs) in all-metal metasurfaces operating at terahertz frequencies. The metasurface integrates several slits with varying lengths, forming gradient slit arrays that enable the generation of multiple quasi-BICs induced by structural symmetry breaking. By tuning the geometric parameters of the slits, the performance of quasi-BICs can be precisely controlled. Experimental findings reveal that two resonances with quality exceeding 40 are induced in three-slit arrays. Results demonstrate that integrating multiple resonators of varying sizes enables the achievement of numerous resonant modes. Benefiting from their fully metallic architecture, such metasurfaces are highly suitable for wave manipulation in terahertz applications.

Extending the terahertz (THz) silicon-based ridge waveguide platform to THz asymmetric topological pumping remains unexplored due to theoretical deficiency and severe coupling inefficiency, which hinder practical deployment for potential THz on-chip 6G applications. Here, we experimentally demonstrate asymmetric topological pumping in a silicon-based terahertz ridge waveguide array operating over 159-171 GHz. A four-channel Rice-Mele (RM) configuration with modulated waveguide widths and spacings enables robust unidirectional transport with over 15 dB contrast across 12 GHz. The device established a CMOS-compatible, broadband, and robust platform for integrated THz photonic circuits.

Seeing clearly through fog, murky water, or other scattering materials is difficult with conventional imaging systems. One powerful tool is polarimetric imaging, which captures how light is polarized to reveal hidden details and material properties. But traditional systems must choose between a wide aperture (for gathering light) and a large depth of field (for keeping the whole scene in focus), limiting their effectiveness in challenging environments. Here we report a metasurface-based polarimetric light field camera capable of single-shot acquisition of five-dimensional (5D) light field data, comprising spatial, angular, and polarization information. A polarization-multiplexed metasurface placed between the main lens and the image sensor serves as an integrated optical encoder, enabling complete 5D capture without moving parts or stacked polarization optics. This configuration supports near-infinite DOF imaging through computational refocusing while maintaining a large aperture. As a proof of concept, we demonstrate all-in-focus polarimetric imaging over a 35 cm depth range in highly turbid water, achieving up to 6.63- and 7.30-fold contrast enhancement relative to the scattered images obtained with a pair of orthogonal linear polarizations. These results establish a compact and scalable pathway to high-dimensional imaging with potential applications in scientific instrumentation, industrial inspection, and environmental sensing.

Here, polarization-controlled bound states in the continuum (BICs) are demonstrated in all-metallic metasurfaces based on complementary periodic cross-shaped resonators (CPCRs) through varying polarization angles, enabling tunable switching between BICs and quasi-BICs. The CPCR features four slits extending from its center, endowing it with highly flexible structural tunability that can be exploited to break symmetry by adjusting the slit length. A simultaneous adjustment of two slit lengths enables the realization of quasi-BICs in both transverse electric (TE) and transverse magnetic (TM) waves. When two slits have equal length, such quasi-BICs show polarization dependence, emerging at a certain angle, disappearing with increasing angle, and then recurring at π intervals. This cyclic pattern persists for slits of unequal lengths. At a critical polarization angle, the electric field alignment transitions to in-phase, confirming the transformation of quasi-BICs to accidental BICs. The polarization angle regulates the transition between these states, enabling the engineering of quasi-BICs with promising applications in the development of filters, sensors, and detectors operating at terahertz frequencies or other spectral bands.

This paper presents a compact dual-band terahertz metamaterial absorber designed for highly sensitive refractive index sensing. The unit cell is composed of a double-square split-ring resonator (DSSRR) on a PTFE dielectric layer with a continuous aluminum ground plane, occupying an ultra-small footprint of 9 & times; 9 & times; 3.4 mu m3. Through systematic optimization of the inner and outer split rings, two distinct absorption peaks are achieved at 5.44 THz and 9.61 THz, both with absorption rates exceeding 99.9%. The absorption mechanism is comprehensively analyzed using impedance matching theory, electric field distributions, and surface current patterns. Numerical simulations demonstrate a high refractive index sensitivity of 3071 GHz/RIU at the higher resonance frequency, outperforming most previously reported terahertz metamaterial sensors. Additionally, the sensor's potential for early cancer detection is evaluated by numerically detecting refractive index variations between healthy and cancerous basal cells. The proposed design combines ultra-compactness, structural simplicity, dual-band operation, and high sensitivity, making it a promising candidate for practical terahertz sensing applications, including biomedical diagnostics, chemical detection, and environmental monitoring.

We propose and experimentally demonstrate liquid crystal- based computer-generated image holography enabled by the Pancharatnam-Berry phase modulation. Such a device exhibits distinctive properties, such as natural light illumination, polarization insensitivity, broadband optical response, high polarization conversion efficiency, and direct visibility to the naked eye. These unique attributes make this type of image holography a promising avenue for applications in optical information storage, anti-counterfeiting, and advanced information displays. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Optical imaging has evolved from capturing light intensity to recording high-resolution, multi-dimensional images with various optical parameters, such as amplitude, phase, polarization, and wavelength. Optical multiparameter imagers are capable of providing detailed insights into objects and scenes by measuring multiple optical parameters. Traditional optical multiparameter imaging systems, such as imaging polarimeters and spectrometers, are bulky and limited in time resolution. Metasurfaces have emerged as a compact solution for multiparameter imaging by enabling the flexible manipulation of light fields. In this review, we highlight recent fundamental advances in optical metasurface multiparameter imaging, including imaging polarimeters, imaging spectrometers, and quantitative phase/depth imagers, as well as their applications in imaging technologies. We also discuss current trends and challenges of applications relying on these imaging technologies, and offer parting thoughts about promising ways to overcome them for the advancement of imaging technologies.

In a non-Hermitian system, dynamically encircling exceptional points (EPs) within the parameter space facilitates chiral mode transfer, wherein the resulting output states are contingent upon the encircling EP direction. However, mainstream two-stage EP-based chiral mode transfer has encountered critical bottlenecks, as current research primarily focuses on operating within a single dimension (polarization or mode). Here, high-dimensional chiral transfer by bi-directionally encircling EPs is presented, which implements distinct chiral transfers for different polarizations. Consequently, the high-dimensional chiral transfer yields unconventional output mode states that are influenced not only by the injection direction but also by the polarization state. Meanwhile, leveraging the birefringence effect of the silicon waveguide, high-performance high-dimensional chiral transfer is experimentally demonstrated using the bi-directionally encircling-EP approach, which demonstrates robustness against encircling loop selection. Moreover, the occurrence of chiral transfer can also be controlled by polarization. The findings not only pave the way for further exploration of high-dimensional non-Hermitian systems but also unlock opportunities for a wide variety of high-capacity applications.

Topological photonic states have garnered a wide range of research interest in photonics due to their robustness against disorders and imperfections. Here, we present a novel topological chiral transfer effect by combining topological pumping and dynamical mode braiding in non-Hermitian photonic lattices. Unlike conventional topological pumping, the transfer of topological edge states (TESs) exhibits dual asymmetry in both the input edge and propagation direction selections. Furthermore, the large energy gap between TESs and bulk states allows relaxation of adiabatic constraints, leading to a two-order-of-magnitude reduction in device length compared to previous designs, as demonstrated by experiments. Our findings not only advance the understanding of multi-degree-of-freedom non-Hermitian dynamics but also offer an accessible approach for developing high-density integrated photonic devices.

The quest for simpler structures that do not require the use of nanofabrication techniques and exhibit high Q Fano resonances has attracted growing interest in the past decade. Here, we study an arrangement of coupled resonator waveguides that can excite Fano resonances. The results show that an odd mode, except for the usual even mode, is excited due to the symmetry breaking of the position stub intersection. The superposition of the even and odd modes generates a Fano-shaped spectrum with a very narrow linewidth. Coupled mode theory is used to analyze these waveguide-based Fano resonances. Experimental results obtained using VNA and VDI show good agreement with theory and simulations. Such waveguide-based Fano resonances can be tailored and are simple in structure and have potential applications in narrowband filtering, sensing, lasing, and nonlinearity enhancement.

The Hall effect of elastic waves has attracted much attention due to its unique properties. A hexagonal lattice phononic crystal plate model is designed in this paper. By changing the spatial symmetry of the unit cell, a band gap for the A(0) Lamb wave is opened. The existence of the edge state of the phononic crystal plate is obtained by finite element simulation. It is found that both zigzag-type edge and bridge edge are topological edge states by analysis of the band structure of the supercell. A rectangular model with a straight channel is designed and the simulation results show that the two types of channels are topologically protected only for the A(0) mode Lamb wave but not for the S-0 mode. In addition, the results of numerical simulation are verified by experimental data measured by a laser vibrometer. Finally, it is found that neither upside V-shaped channels nor channels with defects will affect the stable propagation of A(0) Lamb waves along the proposed route. This proposed model and method are helpful in broadening the means of regulating elastic waves in phononic crystal structures, and extending practical application of topological edge states in such structures.

The rapid advancement of topological photonics has opened up a promising frontier for manipulating optical fields. Among various emerging strategies, topological micro-/nano-structures have garnered growing interest, offering enhanced robustness to photonic devices and providing a compact platform for tailoring multiple physical dimensions of optical fields. In this paper, we summarize recent advances in topological micro-/nano-structures for tailoring light. We begin with an introduction to the fundamental concepts of topology, topological photonics, topological micro-/nano-structures, and multidimensional photonics. We then highlight representative works, including gain/loss structures based on the exceptional points, on-chip topological array waveguides, boundary state waveguides, valley photonic crystal waveguides, and micro-/nano-scale devices based on bound states in the continuum. Finally, we discuss future challenges and opportunities in light field manipulation using topological micro-/nano-structures.

In this work, we theoretically simulated the photonic band structures of the proposed photonic crystal based on two-dimensional V-shaped dielectric pillars with the same V-direction and opposite V-direction. The flat-band behavior throughout the entire Brillouin zone was investigated by analyzing the bandwidth variations with optimized parameters and other performances such as electric field distribution and group index. The bandwidth can reach the minimum value of Δωa/2πc=0.00888 and 0.00579 for two cases. The results provide support for searching the flat band throughout the entire Brillouin zone in photonic crystals.

The terahertz spectral region has garnered significant attention for label-free chemical and biological sensing due to its molecular fingerprints, low energy characteristics, and remote sensing capabilities. Microfluidic platforms are particularly attractive because microchannels are made from inexpensive biocompatible materials, preventing environmental contamination, and require only micro to nanolitre sample volumes for manipulation. These platforms offer the advantages of simple design, easy fabrication, lightweight prototypes, and real-time measurements. In this manuscript, we review state-of-the-art terahertz microfluidic technology with a focus on liquid-based high sensitivity terahertz microfluidic devices and systems. This includes material platforms, the physical mechanisms underlying their characterization methods, and fabrication methodologies. Next, we explore further applications of microfluidics, such as the optoacoustic effect, particle capture, active amplitude control, frequency-agile multiplexing, imaging, and signal processing. Finally, the future prospects of terahertz microfluidic in biochemical sensing applications are also discussed.

A tunable broadband terahertz absorber based on five square rings of vanadium dioxide (VO2) is proposed in this paper. We use a CST software to simulate the absorption characteristics of the absorber. The results show that the bandwidth of the absorber, with absorption exceeding 90%, reached 2.51 THz from 2.71 to 5.22 THz. The electric and surface current distributions reveal that the high absorption is due to the dipole resonance and coupling of the square rings. The absorption peak can be approximately tuned from 2% to 99.5% by varying the conductivity of VO2 from 200 S/m to 200,000 S/m. In addition, the absorber has polarization insensitivity and can maintain good absorption performance over a wide range of incident angles. The designed absorber is expected to be widely used in areas of terahertz communication, imaging, and detection. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Optical imaging,as a cornerstone of modern optical research,bears significant ap-plication value in both scientific exploration and engineering technologies.Fresnel diffraction theory reveals that when imaging a point source through an optical system,the interplay be-tween light's wave nature and finite lens aperture induces diffraction effects,generating an Airy disk whose spatial extent defines the Rayleigh diffraction limit.While current undergrad-uate curricula predominantly utilize Fresnel diffraction integrals for imaging resolution analy-sis,this study adopts a Fourier optics framework to rigorously derive the angular spectrum propagation of point-source radiation,thereby fundamentally unveiling the diffraction-limited nature of conventional lens systems.The first zero point of the intensity distribution in the circular aperture diffraction pattern is obtained through numerical solution based on the Fou-rier angular spectrum method,and the result is compared with that calculated using the Ray-leigh criterion.By further integrating cutting-edge developments in negative-refraction optics,we systematically elucidate the physical principles enabling negative-index metamaterials to overcome classical diffraction constraints.This work not only establishes a novel pedagogical paradigm for optical imaging theory but also provides a critical analytical framework for super-resolution imaging research,serving as a conceptual bridge between undergraduate optics edu-cation and advanced graduate studies in photonic innovation.

Terahertz attenuated total reflection (ATR) technique serves as a pivotal tool for the spectroscopic analysis of liquids. However, when measuring liquids, conventional single internal reflection probes exhibit low sensitivity and detection accuracy due to the limited interaction between the evanescent wave and the sample. To address this limitation, we designed and constructed a terahertz liquids ATR probe utilizing a triple internal reflection prism, which effectively enhances the interaction between the evanescent wave and the liquid by increasing the number of reflections within the prism. Experimental results demonstrate that the terahertz triple ATR probe achieves high accuracy in measuring the sample's optical constants. By exploiting the differences in terahertz wave absorption among different polar solvents, the proposed probe effectively recognizes polar solvents such as ethanol, water, isopropanol, and acetone. In terms of sensor performance, the sensitivity of our probe, which employs a triple internal reflection scheme, is three times that of a conventional single internal reflection probe. This increased sensitivity further enhances the accuracy of measuring small changes in solution composition.