Lossless dielectric metasurface with giant intrinsic chirality for terahertz wave

Dielectric metasurface-assisted terahertz sensing: mechanism, fabrication, and multiscenario applications

Terahertz (THz) technology has attracted significant global interest, particularly in sensing applications, due to its nonionizing feature and sensitivity to weak interactions. Recently, owing to the advantages of low optical loss and the capability to support both electric and magnetic high-quality factor (high-Q) resonances, dielectric metasurfaces have emerged as a powerful platform for multiscenario terahertz sensing applications. This review summarizes recent advancements in dielectric metasurface-assisted THz sensing. We begin with an overview of the mechanisms and properties of dielectric metasurfaces with high-Q factors. Next, we discuss typical fabrication techniques for these terahertz dielectric metasurfaces. We then explore the diverse terahertz sensing applications across various scenarios, including biomolecule sensing, biomedical detection, environmental monitoring, and chiral sensing. Finally, we provide perspectives on the future development of this promising research field.

Tunable metasurfaces for implementing terahertz controllable NOT logic gate functions

Compared with traditional electrical logic gates, optical or terahertz (THz) computing logic gates have faster computing speeds and lower power consumption, and can better meet the huge data computing needs. However, there are limitations inherent in existing optical logic gates, such as single input/output channels and susceptibility to interference. Here, we proposed a new approach utilizing polarization-sensitive graphene-vanadium dioxide metasurface THz logic gates. Benefitting from two actively tunable materials, the proposed controlled-NOT logic gate(CNOT LG) enables versatile functionality through a dual-parameter control system. This system allows for the realization of multiple output states under diverse polarized illuminating conditions, aligning with the expected input-output logic relationship of the CNOT LG. Furthermore, to demonstrate the robustness of the designed THz CNOT LG metasurface, we designed an imaging array harnessing the dynamic control capabilities of tunable meta-atoms, facilitating clear near-field imaging. This research is promising for advancing CNOT LG applications in the THz spectrum. It has potential applications in telecommunications, sensing, and imaging.

Phase distribution and circular dichroism switchable terahertz chiral metasurface

Chiral metasurfaces have many applications in the terahertz (THz) band, but they still lack modulation flexibility and functionality expansion. This paper presents a terahertz chiral metasurface with switchable phase distribution and switchable circular dichroism (CD). The metasurface unit consists of a metallic inner ring embedded in vanadium oxide and a vanadium oxide outer ring, state switching by thermal control of vanadium oxide and a change in the frequency of the incident wave. Based on the switchable phase distribution, we designed a focusing vortex beam generator with adjustable focal lengths through simulation. Based on the switching CD capability, we simulate its mode switching in near-field imaging using numerical simulation, and innovatively propose an optical encryption method. Utilizing the chiral property, we also designed dual-channel switchable holographic imaging in the same frequency band, which combined with the state change of VO2 can realize a total of 4 holograms switching. Our proposed metasurface is expected to provide new ideas for the study of optical encryption and wavefront modulation of dynamics.

Simultaneous broadband and high circular dichroism with two-dimensional all-dielectric chiral metasurface

Chiral metasurfaces have great potential in various applications such as polarimetric imaging and biomedical recognition. However, simultaneous broadband and high circular dichroism (CD) with high polarization extinction ratio (PER) remains a challenge. Here, we present a novel approach to realize simultaneous broadband and high CD with high PER in the optical communication band using a two-dimensional all-dielectric chiral metasurface. The structure is formed by a two-level chiral structure of split cross (first-order) and trapezoid-shaped (second-order) of Si nano ribs, respectively, in which constructively coupled first- and second-order of chirality occurs, resulting in the broad chiral response in the far field of multipoles excited by incident light of different chiralities. Theoretical results show that a CD in transmission reaching 0.9 (up to 0.993) and a PER exceeding 20 dB (up to 35 dB) over the entire wavelength range from 1.39 to 1.61 μm can be achieved simultaneously, consistent with the experimental results of CD ∼0.9 and PER of 10 dB (up to 19.7 dB). Our design paves the way for chiral metasurfaces toward practical applications in terms of working bandwidth, high CD and PER as well as integrality of the devices in many fields.

Chiral metasurface zone plate for transmission-reflection focusing of circularly polarized terahertz waves

The properties of traditional Fresnel zone plates have been greatly enhanced by metasurfaces, which allow the control of polarization, orbital angular momentum, or other parameters on the basis of focusing. In this Letter, a new, to the best of our knowledge, method for circularly polarized wave manipulation based on a zone plate is proposed. Chiral meta-atoms and binary geometric phase are used for the simultaneous focusing of reflected and transmitted terahertz waves. The silicon-based dielectric chiral units, which show great performance of spin-selective transmission near 0.54 THz, separate the orthogonal circularly polarized components. A binary Pancharatnam-Berry (P-B) phase gradient is obtained by rotating the unit 90 degrees, then the phase zone plate can be easily designed. The simulation results show that the proposed chiral metasurface zone plate has the function of reflection-transmission separation and focusing for the circularly polarized terahertz waves. In addition, we also demonstrate the possibility of using a 1064-nm continuous infrared laser to adjust the intensity of our devices, based on photo-generated carriers in silicon. The design principle of the chiral metasurface zone plates can be extended to other wavelengths, providing new ideas for the regulation of circularly polarized light.

Dual-band terahertz all-silicon metasurface with giant chirality for frequency-undifferentiated near-field imaging

Chiral metasurfaces are widely used in imaging and biosensing due to their powerful light field control capabilities. Most of the work is devoted to achieving the goals of chirality enhancement and tunability, but lacks consideration of design complexity, loss, cost, and multi-band operation. In order to alleviate this situation, we propose a pair of dual-frequency giant chiral structures based on all-silicon, which can achieve excellent and opposite spin-selective transmission around 1.09 THz and 1.65 THz. The giant chirality derives from the in-plane electric and magnetic dipole moments excited in different degrees. Theoretically, the maximum circular dichroism at the two frequencies are both as high as 0.34, and the coverage bandwidths of the two giant chirality are 85.5 GHz and 41.4 GHz, respectively. The experimental results are in good agreement with the simulation results. Based on the dual-band giant chiral patterns, the terahertz near-field imaging of different Chinese character images is demonstrated at two frequencies. The frequency-undifferentiated characteristics, good intensity contrast and three-dimensional imaging information are shown by the results. This work provides new ideas for the design of terahertz devices with simple structure and multi-functions, which are expected to be applied in the field of terahertz imaging or multi-channel communication.