Terahertz (THz) metamaterials, with their exceptional ability to precisely manipulate the phase, amplitude, polarization and orbital angular momentum (OAM) of electromagnetic waves, have demonstrated significant application potential across a wide range of fields. However, traditional design methodologies often rely on extensive parameter sweeps, making it challenging to address the increasingly complex and diverse application requirements. Recently, the integration of artificial intelligence (AI) techniques, particularly deep learning and optimization algorithms, has introduced new approaches for the design of THz metamaterials. This paper reviews the fundamental principles of THz metamaterials and their intelligent design methodologies, with a particular focus on the advancements in AIdriven inverse design of THz metamaterials. The AIdriven inverse design process allows for the creation of THz metamaterials with desired properties by working backward from the unit structures and array configurations of THz metamaterials, thereby accelerating the design process and reducing both computational resources and time. It examines the critical role of AI in improving both the functionality and design efficiency of THz metamaterials. Finally, we outline future research directions and technological challenges, with the goal of providing valuable insights and guidance for ongoing and future investigations.

With the progression of photolithography processes, the present technology nodes have attained 3 nm and even 2 nm, necessitating a transition in the precision standards for displacement measurement and alignment methodologies from the nanometer scale to the subnanometer scale. Metasurfaces, owing to their superior light field manipulation capabilities, exhibit significant promise in the domains of displacement measurement and positioning, and are anticipated to be applied in the advanced alignment systems of lithography machines. This paper primarily provides an overview of the contemporary alignment and precise displacement measurement technologies employed in photolithography stages, alongside the operational principles of metasurfaces in the context of precise displacement measurement and alignment. Furthermore, it explores the evolution of metasurface systems capable of achieving nano/subnano precision, and identifies the critical issues associated with subnanometer measurements using metasurfaces, as well as the principal obstacles encountered in their implementation within photolithography stages. The objective is to provide initial guidance for the advancement of photolithography technology.

Topological insulators represent a new phase of matter, characterized by conductive surfaces, while their bulk remains insulating. When the dimension of the system exceeds that of the topological state by at least two, the insulators are classified as higherorder topological insulators (HOTI). The appearance of higherorder topological states, such as corner states, can be explained by the filling anomaly, which leads to the fractional spectral charges in the unit cell. Previously reported fractional charges have been quite limited in number and size. In this work, based on the twodimensional (2D) SuSchriefferHeeger model lattice, we demonstrated a new class of HOTIS with adjustable fractional charges that can take any value ranging from 0 to 1, achieved by utilizing the Lorentz transformation. Furthermore, this transformation generates novel boundstateincontinuumlike corner states, even when the lattice is in a topological trivial phase, offering a new approach to light beam localization. This work paves the way for fabricating HOTIs with diverse corner states that offer promising applicative potential.

Second harmonic generation (SHG), a fundamental and widelystudied phenomenon in nonlinear optics, has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics. While the dominant SHG research has been focused on the optical and infrared regimes, its investigation in the microwave range presents challenges due to the requirements of materials with higher nonlinear coefficients and highpower microwave sources. Here, we provide an overview of methods together with underlying mechanisms for SHG in microwave frequencies, and discuss prospects and insights into the future developments of SHGbased technologies. The discussions on both numerical analyses and experimental studies will offer guidance for further SHG research and communication advancements in microwave regime.

The integrated waveguide polarizer is essential for photonic integrated circuits, and various designs of waveguide polarizers have been developed. As the demand for dense photonic integration increases rapidly, new strategies to minimize the device size are needed. In this paper, we have inversely designed an integrated transverse electric pass (TEpass) polarizer with a footprint of 2.88 µmx 2.88 µm, which is the smallest footprint ever achieved. A direct binary search algorithm is used to inversely design the device for maximizing the transverse electric (TE) transmission while minimizing transverse magnetic (TM) transmission. Finally, the inversedesigned device provides an average insertion loss of 0.99 dB and an average extinction ratio of 33 dB over a wavelength range of 100 nm.

Multispectral imaging plays a crucial role in simultaneously capturing detailed spatial and spectral information, which is fundamental for understanding complex phenomena across various domains. Traditional systems face significant challenges, such as large volume, static function, and limited wavelength selectivity. Here, we propose an innovative dynamic reflective multispectral imaging system via a thermally responsive cholesteric liquid crystal based planar lens. By employing advanced photoalignment technology, the phase distribution of a lens is imprinted to the liquid crystal director. The reflection band is reversibly tuned from 450 nm to 750 nm by thermally controlling the helical pitch of the cholesteric liquid crystal, allowing selectively capturing images in different colors. This capability increases imaging versatility, showing great potential in precision agriculture for assessing crop health, noninvasive diagnostics in healthcare, and advanced remote sensing for environmental monitoring.

A polarization converter with broadband polarization characteristics and capable of dynamic reconfiguration is proposed. By introducing outofplane degrees of freedom, dynamically tunable broadband and highefficiency linear polarization conversion within the wavelength range of 20002800 nm is achieved. Research results indicate that when a twodimensional (2D) splitring resonator (SRR) is irradiated by a lowdose focused ion beam, it will deform upward and transform into a threedimensional (3D) SRR, achieving a linear polarization conversion efficiency of over 90%. The 3D SRR can be driven by electrostatic force to return to the 2D SRR state, thereby realizing the dynamic reconfiguration of this polarization converter. By changing the applied voltage and adjusting the structural parameters, a tailored polarization converter that exhibits broadband performance and high polarization conversion efficiency is also achieved. The results may provide novel ideas and technical methodologies for various applications such as polarized optical imaging, emerging display technologies, polarized optical communication, and optical sensing.

Optical microscopes are essential tools for scientific research, but traditional microscopes are restricted to capturing only twodimensional (2D) texture information, lacking comprehensive threedimensional (3D) morphology capabilities. Additionally, traditional microscopes are inherently constrained by the limited spacebandwidth product of optical systems, resulting in restricted depth of field (DOF) and field of view (FOV). Attempts to expand DOF and FOV typically come at the cost of diminished resolution. In this paper, we propose a texturedriven FOV stitching algorithm specifically designed for extended depthoffield (EDOF) microscopy, allowing for the integration of 2D texture and 3D depth data to achieve highresolution, highthroughput multimodal imaging. Experimental results demonstrate an 11fold enhancement in DOF and an 8fold expansion in FOV compared to traditional microscopes, while maintaining axial resolution after FOV extension.