Imaging-based terahertz pixelated metamaterials for molecular fingerprint sensing.

With the rapid development of terahertz-enabled devices, the study of miniaturized and integrated systems has attracted significant attention. We experimentally demonstrate an imaging-based pixelated metamaterial for detecting terahertz molecular fingerprints related to intermolecular vibrations and large-amplitude intramolecular modes, including chemical identification and compositional analysis. The compact THz sensor consists of a 4 × 4 pixelated filter-detector array with transmission resonances tuned to discrete frequencies.

Physics-Informed Inverse Design of Programmable Metasurfaces.

Emerging reconfigurable metasurfaces offer various possibilities for programmatically manipulating electromagnetic waves across spatial, spectral, and temporal domains, showcasing great potential for enhancing terahertz applications. However, they are hindered by limited tunability, particularly evident in relatively small phase tuning over 270°, due to the design constraints with time-intensive forward design methodologies. Here, a multi-bit programmable metasurface is demonstrated capable of terahertz beam steering facilitated by a developed physics-informed inverse design (PIID) approach.

Linear and phase controllable terahertz frequency conversion via ultrafast breaking the bond of a meta-molecule.

The metasurface platform with time-varying characteristics has emerged as a promising avenue for exploring exotic physics associated with Floquet materials and for designing photonic devices like linear frequency converters. However, the limited availability of materials with ultrafast responses hinders their applications in the terahertz range. Here we present a time-varying metasurface comprising an array of superconductor-metal hybrid meta-molecules.

Modulo-addition operation enables terahertz programmable metasurface for high-resolution two-dimensional beam steering.

Electrically controlled terahertz (THz) beamforming antennas are essential for various applications such as wireless communications, security checks, and radar to improve coverage and information capacity. The emerging programmable metasurface provides a flexible, cost-effective platform for THz beam steering. However, scaling such arrays to achieve high-gain beam steering faces several technical challenges.

Antireflection Coatings Based on PEDOT:PSS Conductive Polymer Using d-Sorbitol Additives for Terahertz Spectroscopy and Imaging.

Optical antireflection has been employed for a variety of applications in terahertz spectroscopy and detectors. However, current methods encounter challenges in terms of cost, bandwidth, structural complexity, and performance. In this study, a low-cost, broadband, and easily processed THz antireflection coating scheme based on the model of impedance-matching effect is proposed, using a 6 wt % d-sorbitol-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (s-PEDOT:PSS) film.

Freestanding narrowband terahertz filters based on aluminum foil.

Terahertz (THz) filters with high transmission coefficient (T) in the passband and frequency selectivity are critical in numerous applications such as astronomical detection and next-generation wireless communication. Freestanding bandpass filters eliminate the Fabry-Pérot effect of substrate, thus providing a promising choice for cascaded THz metasurfaces. However, the freestanding bandpass filters (BPFs) using the traditional fabrication process are costly and fragile.

Directional terahertz holography with thermally active Janus metasurface.

Dynamic manipulation of electromagnetic (EM) waves with multiple degrees of freedom plays an essential role in enhancing information processing. Currently, an enormous challenge is to realize directional terahertz (THz) holography. Recently, it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions, making multiplexed dynamic manipulation of THz waves possible.

Terahertz Spin Current Dynamics in Antiferromagnetic Hematite.

An important vision of modern magnetic research is to use antiferromagnets (AFMs) as controllable and active ultrafast components in spintronic devices. Hematite (α-Fe O ) is a promising model material in this respect because its pronounced Dzyaloshinskii-Moriya interaction leads to the coexistence of antiferromagnetism and weak ferromagnetism. Here, femtosecond laser pulses are used to drive terahertz (THz) spin currents from α-Fe O into an adjacent Pt layer.

Electrically addressable integrated intelligent terahertz metasurface.

Reconfigurable intelligent surfaces (RISs) play an essential role in various applications, such as next-generation communication, uncrewed vehicles, and vital sign recognizers. However, in the terahertz (THz) region, the development of RISs is limited because of lacking tunable phase shifters and low-cost sensors. Here, we developed an integrated self-adaptive metasurface (SAM) with THz wave detection and modulation capabilities based on the phase change material.

Active and tunable nanophotonic metamaterials.

Metamaterials enable subwavelength tailoring of light-matter interactions, driving fundamental discoveries which fuel novel applications in areas ranging from compressed sensing to quantum engineering. Importantly, the metallic and dielectric resonators from which static metamaterials are comprised present an open architecture amenable to materials integration. Thus, incorporating responsive materials such as semiconductors, liquid crystals, phase-change materials, or quantum materials (e.

Picosecond mode switching and Higgs amplitude mode in superconductor-metal hybrid terahertz metasurface.

The ultrafast modulation of terahertz (THz) waves is essential for numerous applications, such as high-rate wireless communication, nonreciprocal transmission, and linear frequency conversion. However, high-speed THz devices are rare due to the lack of materials that rapidly respond to external stimuli. Here, we demonstrate a dynamic THz metasurface by introducing an ultrathin superconducting microbridge into metallic resonators to form a superconductor-metal hybrid structure.

Dual-color terahertz spatial light modulator for single-pixel imaging.

Spatial light modulators (SLM), capable of dynamically and spatially manipulating electromagnetic waves, have reshaped modern life in projection display and remote sensing. The progress of SLM will expedite next-generation communication and biomedical imaging in the terahertz (THz) range. However, most current THz SLMs are adapted from optical alternatives that still need improvement in terms of uniformity, speed, and bandwidth.

Infrared all-dielectric Kerker metasurfaces.

The unidirectional scattering of electromagnetic waves in the backward and forward direction, termed Kerkers' first and second conditions, respectively, is a prominent feature of sub-wavelength particles, which also has been found recently in all-dielectric metasurfaces. Here we formulate the exact polarizability requirements necessary to achieve both Kerker conditions simultaneously with dipole terms only and demonstrate its equivalence to so-called "invisible metasurfaces". We further describe the perfect absorption mechanism in all-dielectric metasurfaces through development of an extended Kerker formalism.

Neural-adjoint method for the inverse design of all-dielectric metasurfaces.

All-dielectric metasurfaces exhibit exotic electromagnetic responses, similar to those obtained with metal-based metamaterials. Research in all-dielectric metasurfaces currently uses relatively simple unit-cell designs, but increased geometrical complexity may yield even greater scattering states. Although machine learning has recently been applied to the design of metasurfaces with impressive results, the much more challenging task of finding a geometry that yields a desired spectra remains largely unsolved.

Role of loss in all-dielectric metasurfaces.

Arrays of dielectric cylinders support two fundamental dipole active eigenmodes, which can be manipulated to elicit a variety of electromagnetic responses in all-dielectric metamaterials. Dissipation is a critical parameter in determining functionality; the present work varies material loss to explore the rich electromagnetic response of this class of metasurface. Four experimental cases are investigated which span electromagnetic response ranging from Huygens surfaces with transmissivity T = 94%, and phase ϕS = 235°, to metasurfaces which absorb 99.

Resonance-domain diffractive lens for the terahertz region.

Diffractive optics has long served as the basis of spectroscopic measurements of materials. Operation in the resonance domain further allows these elements to achieve high efficiency and polarization control. An effective grating theory is a practical tool for modeling such optics, and here we extend use of this theory to the terahertz region, experimentally demonstrating an all-dielectric binary off-axis diffractive lens.

Phototunable Dielectric Huygens' Metasurfaces.

Conventional dielectric metasurfaces achieve their properties through geometrical tuning and consequently are static. Although some unique properties are demonstrated, the usefulness for realistic applications is thus inherently limited. Here, control of the resonant eigenmodes supported by Huygens' metasurface (HMS) absorbers through optical excitation is proposed and demonstrated.

Multiplexed coded time domain sampling with metamaterials.

The far infrared region of the electromagnetic spectrum often necessitates the use of thermal detectors that, by nature, typically have poor response times and diminished sensitivities, at least compared to adjacent bands. However, many signals of interest contain frequency components far too fast to be reliably measured with such detectors, and hence expensive and inefficient alternatives are brought to bear. Here we propose and experimentally validate a new method leveraging the speed and scalability of dynamic metamaterial modulators to encode high-frequency signal components at a lower frequency, making them reliably measurable with thermal detectors that would otherwise be too slow.

Graphene metamaterial spatial light modulator for infrared single pixel imaging.

High-resolution and hyperspectral imaging has long been a goal for multi-dimensional data fusion sensing applications - of interest for autonomous vehicles and environmental monitoring. In the long wave infrared regime this quest has been impeded by size, weight, power, and cost issues, especially as focal-plane array detector sizes increase. Here we propose and experimentally demonstrated a new approach based on a metamaterial graphene spatial light modulator (GSLM) for infrared single pixel imaging.

Graphene metamaterial modulator for free-space thermal radiation.

We proposed and demonstrated a new metamaterial architecture capable of high speed modulation of free-space space thermal infrared radiation using graphene. Our design completely eliminates channel resistance, thereby maximizing the electrostatic modulation speed, while at the same time effectively modulating infrared radiation. Experiment results verify that our device with area of 100 × 120 µm can achieve a modulation speed as high as 2.

Voltage-tunable dual-layer terahertz metamaterials.

This paper presents the design, fabrication, and characterization of a real-time voltage-tunable terahertz metamaterial based on microelectromechanical systems and broadside-coupled split-ring resonators. In our metamaterial, the magnetic and electric interactions between the coupled resonators are modulated by a comb-drive actuator, which provides continuous lateral shifting between the coupled resonators by up to 20 μm. For these strongly coupled split-ring resonators, both a symmetric mode and an anti-symmetric mode are observed.

Nonlinear terahertz devices utilizing semiconducting plasmonic metamaterials.

The development of responsive metamaterials has enabled the realization of compact tunable photonic devices capable of manipulating the amplitude, polarization, wave vector and frequency of light. Integration of semiconductors into the active regions of metallic resonators is a proven approach for creating nonlinear metamaterials through optoelectronic control of the semiconductor carrier density. Metal-free subwavelength resonant semiconductor structures offer an alternative approach to create dynamic metamaterials.