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.

Terahertz hollow core negative curvature fiber (HCNCF) offers high-performance waveguiding but face fabrication challenges due to complex processes. In this article, we present a simple and cost-effective new paradigm, the film-to-fiber method, utilizing commercial polyimide (PI) films to form a typical six-cladding-tube HCNCF structure. Additionally, metal microstructures can be integrated onto the PI film to enhance waveguiding properties. Three HCNCF types—without metal structures, with full metal integration, and with selective metal placement—are fabricated and characterized using terahertz time-domain spectroscopy system across 0.2–1.5 THz. Experimental results, including experimental loss, refractive index (birefringence), dispersion, and other parameters, align well with numerical simulations. This study introduces a cost-effective and flexible fabrication approach that accommodates polymer films of arbitrary thickness, providing a new paradigm for HCNCF manufacturing and advancing terahertz applications.

We proposed and numerically investigated an analogue of electromagnetically induced transparency (EIT) all-dielectric metasurface that features one asymmetric S-shaped silicon resonator in the unit cell and generates high transparency, high Q-factor resonance in the near infrared spectral region. Breaking the symmetry of the S-shaped structure could provide a pathway to excite a trapped magnetic mode that coupled to a bright electric dipolar moment, achieving a sharp EIT-like response. And the Q value of the resonance can be easily modified by altering the asymmetric degree of the structure. In particular, the transparency window will almost maintain its symmetric shape and high transmission of 97%, but shift accordingly as the structural parameters (silicon bar's length, width, or thickness) vary in a large range, because of the very small detuning between the two coupled modes. The proposed S-shaped all-dielectric metasurface could ease fabrication challenges and have potential applications in bio-chemical sensing, narrowband filters, optical modulations, and slow light devices.

Negative curvature fibers have the benefits of high bandwidth, low loss, and provide higher transmission performances. Birefringence of the fiber is particularly important, with potential application value in communication, imaging and other fields. In this paper, a metasurface structure-assisted terahertz negative curvature fiber is designed to improve the birefringence characteristic. This work breaks through the conditional design ideas, and theoretically analyzes the effect of adding gold microstructures in the cladding structures on the transmission characteristics of negative curvature fibers. The investigation results show that the birefringence of the designed fiber exhibits a significant increase in most frequency range between 1.75–2.4 THz compared to the results before adding gold microstructures. The maximum birefringence reaches as high as 0.00216 when the frequency is 2.175 THz and θ is 90°. Compared to the original frequency, the birefringence has increased by nearly an order of magnitude. The highest birefringence has been increased to 3.5 times. In addition, the influences of the gold microstructures on the confinement loss, waveguide dispersion, and effective mode field area are also investigated. This fiber provides a reference for the design of high birefringence terahertz fibers in the future.

The rapid and precise identification of multiple pathogens is critical for ensuring food safety, controlling epidemics, diagnosing diseases, and monitoring the environment. However, traditional detection methods are hindered by complex workflows, the need for skilled operators, and reliance on sophisticated equipment, making them unsuitable for rapid, on-site testing. Optical biosensors, known for their rapid analysis, portability, high sensitivity, and multiplexing capabilities, offer a promising solution for simultaneous multi-pathogenic identification. This paper explores recent advancements in the utilization of optical biosensors for multiple pathogenic detection. First, it provides an overview of key sensing principles, focusing on colorimetric, fluorescence-based, surface-enhanced Raman scattering (SERS), and surface plasmon resonance (SPR) techniques, as well as their applications in pathogenic detection. Then, the research progress and practical applications of optical biosensors for multiplex pathogenic detection are discussed in detail from three perspectives: microfluidic devices, nucleic acid amplification technology (NAAT), and nanomaterials. Finally, the challenges presented by optical biosensing technologies in multi-pathogen detection are discussed, along with future prospects and potential innovations in the field.