Optical active Pancharatnam–Berry coding metasurfaces for amplitude modulation of terahertz beams.

To a large extent, the dense extracellular matrix (ECM), which tightly connects tumor cells to arm the tumor into an intractable fortress, significantly decreases the nanoparticles delivery efficacy and overall performance in cancer treatments. Therefore, it is necessary to transform the dense stroma of solid tumors to loose state, which could realize deep penetration of nanomedicine and enhance cancer treatment effects. Here, we fabricated a protein-free collagen nanosweeper, triphenylphosphonium bromide (TPP) coated and S-nitrosothiols loaded mini-sized Au@silica nanorod (Au@SiO₂-SNO/PEG/TPP, GSNP-TPP), to clear the transport barriers of nanoparticles as well as elevate enhanced permeability and retention (EPR) effect, thus alleviating the diffusion resistance and realizing further penetration of nanoparticles.

Using orbital angular momentum (OAM) modes can effectively enhance the information capacity of communication systems. To achieve high-performance OAM transmission characteristics in optical fiber waveguides, it is essential to minimally excite higher-order radial OAM modes in the optical fiber waveguide. Here, we propose two novel mechanisms to suppress the guidance of second-order radial OAM modes in the newly designed dual-core hollow-core fiber, while ensuring the support of a larger number of OAM modes. A detailed analysis process is also performed. The first method obtains the mode patterns and conducts a mathematical analysis based on the cutoff conditions for vector modes. The designed fiber structure is capable of supporting 10 and 30 OAM modes in the outer and inner rings, respectively, within the frequency band of 0.13–0.16 THz. The second approach leverages the coupling effect between two ring cores to achieve the inhibition of high-order radial OAM modes in the core area. This fiber structure supports the transmission of 42 (in) + 74 (out) OAM modes over the span of 0.25–0.35 THz. At the same time, a comparative analysis is conducted on the waveguide dispersion, effective mode field area, confinement loss, mode purity, effective refractive index, and isolation parameters of the two fiber structures. The two methods proposed in this study for suppressing higher-order radial modes can be applied to OAM multiplexing in fiber waveguides under different conditions, which will further increasing the communication capacity of the communication system, this will and also enhance the stability of OAM mode transmission.

When metamaterial structures meet functional materials, what will happen? The recent rise of the combination of metamaterial structures and functional materials opens new opportunities for dynamic manipulation of terahertz wave. The optical responses of functional materials are greatly improved based on the highly-localized structures in metamaterials, and the properties of metamaterials can in turn be manipulated in a wide dynamic range based on the external stimulation. In the topical review, we summarize the recent progress of the functional materials-based metamaterial structures for flexible control of the terahertz absorption and polarization conversion. The reviewed devices include but are not limited to terahertz metamaterial absorbers with different characteristics, polarization converters, wave plates, and so on. We review the dynamical tunable metamaterial structures based on the combination with functional materials such as graphene, vanadium dioxide (VO₂) and Dirac semimetal (DSM) under various external stimulation. The faced challenges and future prospects of the related researches will also be discussed in the end.

Electromagnetic metasurfaces are artificial 2D structures with sub‐wavelength size and have achieved a variety of functions. Coding metasurfaces or programmable metasurfaces are special phase‐manipulation type metasurfaces, which can be used for dynamic electromagnetic modulation and information processing in microwave band. However, programmable or tunable coding metasurfaces in terahertz band are still rare. All‐optical switchable coding metasurfaces based on vanadium dioxide (VO₂) hybrid resonators are proposed for dynamic modulation of terahertz waves. The C‐shaped metal–VO₂ hybrid resonators are switched from anisotropic structures to quasi‐isotropic ones due to insulator–metal transition of VO₂, resulting in great attenuation of conversion efficiency for linearly polarized waves and Pancharatnam–Berry phase for circularly polarized waves. Based on this principle, several coding metasurfaces are shown for efficient and simultaneous switching of wavefront and polarization state of terahertz beams, including linearly and circularly polarized waves. It is worth mentioning that a new method for switchable shared‐aperture metasurfaces is also proposed, in which only a part of the unit cells are integrated with VO₂ and tunable. This new scheme promotes the applications of terahertz coding metasurfaces such as high‐speed terahertz communication.