Nonlinear optics underpins a broad range of photonic technologies, from classical and quantum light sources to emerging nonlinear photonic neural networks. Yet, conventional nonlinear optical devices exhibit static functionality: their transfer characteristics and emission profiles are dictated by the intrinsic nonlinear process and locked by fabrication, limiting adaptability. Here, we introduce an ultra-thin metasurface platform that enables dynamic reconfiguration of nonlinear functionality in a contact-less fashion. By leveraging all-optical control of the optical torque exerted on liquid crystal molecules infiltrating a resonant metasurface, we achieve tunable polynomial nonlinear transfer functions based on third-harmonic generation process. This mechanism further allows real-time modulation of nonlinear weighting across different diffraction orders, revealing a previously unexplored interplay between mode structure and nonlinear emission. Our approach opens up a pathway toward field-programmable nonlinear photonic systems, offering unprecedented flexibility for reconfigurable nonlinear signal processing and adaptive photonic computing.

Developing cost-effective oxygen reduction reaction (ORR) electrocatalysts with simultaneously enhanced activity and durability remains a critical challenge for zinc-air batteries (ZABs). Herein, a multi-heteroatom-doping and defect co-engineering strategy is proposed to construct nitrogen, phosphorus, and sulfur tridoped hollow carbon nanocages (NPS-HCs) through a facile template-induced pyrolysis of a ZIF-8@PZS precursor. The synergistic effect of multi-heteroatom doping and introducing defects creates abundant active species, while the hollow architecture facilitates mass/electron transport during the ORR process. As a result, the optimized NPS-HC-900 catalyst demonstrates exceptional ORR performance with a high half-wave potential (E1/2 = 0.87 V vs RHE). Impressively, the NPS-HC-900 + IrO2-assembled rechargeable ZABs achieve an ultralong cycling stability over 1000 h. In situ spectroscopy and theoretical calculations verify that this synergistic effect promotes the conversion of key intermediate *OOH to *O, thereby significantly facilitating the ORR o. This work provides a paradigm-shifting platform for designing high-performance multi-heteroatom-doped carbon electrocatalysts via synergistic defect engineering.

A mechanically tunable metamaterial concept for transmissive spectral discrimination within the long‐wavelength infrared (LWIR) range (8–12 μm) is proposed and validated. The metamaterial consists of a periodically perforated gold membrane that exhibits the extraordinary optical transmission (EOT) effect, combined with a parallel silicon membrane separated by an air gap. This structure acts as a band‐pass filter, with its spectral position highly sensitive to the separation gap between the membranes, which influences the resonance conditions for EOT. Numerical simulations predict tunability across the entire LWIR range with a membrane displacement of just 0.5 μm. This concept is experimentally demonstrated through vertical electrostatic actuation of the silicon membrane relative to the gold layer facilitated by a micro‐electromechanical systems (MEMS) approach. The measured optical transmission of the fabricated MEMS‐enabled, spectrally tunable plasmonic metamaterial shows good agreement with the numerically modeled spectral filter characteristics. Further refinement of this method could pave the way for a variety of low‐cost, low‐power miniature devices, enhancing spectroscopy and multispectral imaging capabilities in the thermal infrared range.

We discuss our advancements in creating a MEMS-enabled tunable plasmonic metamaterial for spectral filtering in the long-wavelength infrared range. We outline the metamaterial design, its simulated transmission, fabrication process, and the design of a microelectromechanical actuator with integrated metamaterial. Additionally, we present the characteristics of the initial fabricated samples and compare them with the modeled results.

All-optical tunability of semiconductor metasurfaces offers unique opportunities for novel time-varying effects, including frequency conversion and light trapping. However, the all-optical processes often induce optical absorption that fundamentally limits the possible dynamic increase of their quality factor (Q-boosting). Here, we propose and numerically demonstrate the concept of large Q-boosting in a single-material metasurface by dynamically reducing its structural anisotropy on a femtosecond timescale. This balance is achieved by excitation with a structured pump and takes advantage of the band-filling effect in a GaAs direct-bandgap semiconductor to eliminate the free-carrier-induced loss. We show that this approach allows a dynamic boosting of the resonance quality factor over orders of magnitude, only limited by the free-carrier relaxation processes. The proposed approach offers complete dynamic control over the resonance bandwidth and opens applications in frequency conversion and light trapping.

Time-variant metasurfaces [1] have recently provided an ultra-fast approach to manipulating the optical response compared with conventional tunable approaches, like thermal and electric tuning. They allow for femtosecond scale switching by tuning under high-energy pumping sources. However, despite the recent advances in this field, the ability to precisely tailor the metasurface bandwidth with ultra-fast time response has not been carefully explored.

Control of terahertz waves offers a profound platform for next-generation sensing, imaging, and information communications. However, all conventional terahertz components and systems suffer from bulky design, sensitivity to imperfections, and transmission loss. We propose and experimentally demonstrate on-chip integration and miniaturization of topological devices, which may address many existing drawbacks of the terahertz technology. We design and fabricate topological devices based on valley-Hall photonic structures that can be employed for various integrated components of on-chip terahertz systems. We demonstrate valley-locked asymmetric energy flow and mode conversion with topological waveguide, multiport couplers, wave division, and whispering gallery mode resonators. Our devices are based on topological membrane metasurfaces, which are of great importance for developing on-chip photonics and bring many features into terahertz technology.

Dielectric metasurfaces hold an exceptional potential for the next generation of tunable optical systems that find applications in sensing, ranging, and imaging. Here, we introduce and demonstrate magnetic field tuning of dielectric metasurfaces infiltrated with liquid crystals. To illustrate this concept, we show how the reorientation of liquid crystal induced by the magnetic field changes the spectrum of the resonant dielectric metasurface. This new magnetic-field tuning approach offers significant advantages over other liquid crystal tuning methods since it does not require pre-alignment or the fabrication of structured electrodes, which are both challenging when dealing with metasurfaces. Furthermore, there are no strict limitations on the thickness of liquid crystal cells. Importantly, our approach allows for gradual tuning of the resonances by changing the magnetic-field orientation and, thereby, shows good promise for highly tunable optical metadevices.

Pure phase modulation of light is vital for a number of optical devices such as spatial light modulators and beam steering in light detection and ranging (LIDAR) technologies. Tunable metasurfaces have recently provided a feasible alternative to existing technologies, allowing for ultra‐high miniaturisation while enabling high transmission efficiency and tunability under small external stimuli. However, despite the recent advances in the field, no pure phase tuning has been demonstrated in transmissive devices, for example, any implementation of continuous phase tuning is accompanied by sizable amplitude modulation or low efficiency. Here, it is shown that the optical anisotropy of the surrounding material can enable phase‐only tuning of optical metasurfaces in the full 2π range with unitary efficiency over a sizable bandwidth. A practical implementation of this concept based on a liquid‐crystal infiltrated metasurface operating in the regime of extreme Huygens condition is further proposed. In this way, the full 2π phase‐only tunability in transmission can be enabled by controlling bias voltage and temperature variation of the surrounding liquid crystal.

Despite their great potential in communication and sensing applications, printed leaky-wave antennas have rarely been reported at mm-wave frequencies. In this paper, tapered leaky-wave antennas operating at 80 GHz are designed, fabricated and experimentally characterized. While most continuous leaky-wave antennas use subwavelength strips or other comparably small elements, in this work, the surface impedance is discretized very coarsely using only three square patches per period. With this architecture, a wide range of surface reactance can be achieved while maintaining a minimum feature size of the metallic pattern that is feasible for printed circuit fabrication. As the analytical solution for the bandstructure of sinusoidally modulated reactance surfaces is inaccurate for coarse discretization, we find it using full-wave simulation. In order to control side lobes effectively, we use a tapered aperture illumination according to the Taylor one-parameter distribution. A comprehensive experimental demonstration is presented, including near-field and far-field measurements. Therewith, we verify the designed aperture illumination and we reveal the origin of spurious far-field features. Side lobes are effectively suppressed and spurious radiation is reduced to -18 dB compared to the main lobe.

We design and demonstrate experimentally the on-chip integration and miniaturization of topological devices for the terahertz technologies. Our devices are based on valley-Hall photonic structures employed for integrated components of on-chip THz systems.

We demonstrate phase-only tuning of optical metasurfaces in the full 2π-range by controlling the optical anisotropy of their surroundings. The concept is exemplified in a liquid crystal infiltrated metasurface tuned by the temperature and bias-voltage.

Dielectric metasurfaces composed of subwavelength resonators are widely employed for manipulating electromagnetic waves over a broad frequency spectrum ranging from microwaves to optics. Here, a novel type of metasurfaces, created by a periodic lattice of elliptical holes fabricated in a thin dielectric membrane, is studied both theoretically and experimentally. Such membrane metasurfaces demonstrate polarization-selective behavior, and they change their specific functionality from a reflective magnetic mirror, for one polarization, to a transparent Huygens' surface, for the orthogonal polarization. Such a polarization dependence is achieved by manipulating the interference of Mie-resonant multipoles through optimizing the design of the elliptic holes in the dielectric membrane. Such membrane metasurfaces can be employed as flat components with polarization-multiplexed functionalities, bringing benefits for the integration of ultracompact signal manipulation systems.

Metamaterials are engineered structures designed to interact with electromagnetic radiation, whereby the frequency range in which metamaterials respond depends on their dimensions. In this paper, it is demonstrated that a metamaterial can be functional in more than one frequency region. An advanced metamaterial is demonstrated that can interact with both terahertz (THz) and near-infrared (NIR) frequencies, concurrently. This work exploits meander line resonators with nanoscale linewidth distributed over microscale areas, and experimentally demonstrates that such a metamaterial can simultaneously interact with NIR and THz waves. The engineered metamaterial acts as a plasmonic grating in the NIR range and simultaneously acts as an array of electric resonators in the THz range. Moreover, the performance of the engineered metamaterial is polarization-independent in both wavelength regions. Finally, a unique feature of the proposed metamaterial is that it enables resonant frequency tuning in the THz region without affecting the NIR response. All these novel advantages of dual-band meander metamaterial make it an ideal alternative for cutting-edge applications such as bi-functional sensing, imaging, filtering, modulation, and absorption.

Matching magnetic and electric responses has proven key to achieving high-efficiency transmissive Huygens' metasurfaces. However, the complex frequency dependence of the required magnetic and electric responses is difficult to control, causing inevitable mismatch and undesired narrowband responses. Here, a rigorous design methodology is proposed to obtain a metasurface in which the Huygens' condition is maintained over a broad bandwidth and range of phase tuning. By utilizing three patterned metallic layers separated by dielectrics, it is shown how the resonant modes with electric and magnetic dipole moments can be controlled almost independently, enabling broadband transparency with controllable dispersion. Representing the resonant elements as series and parallel inductance-capacitance configurations, a convenient implementation of a macro-level design into a realistic geometry is demonstrated. Based on the proposed method, a subwavelength thickness metasurface lens that maintains constant focal length over 11% of fractional bandwidth is designed and characterized. It is also shown that the method can be utilized to achieve specified values of chromatic dispersion of a metasurface lens, enabling various functional devices and applications.

The possibility of making an object invisible for detectors has become a topic of considerable interest over the past decades. Most of the studies so far focused on reducing the visibility by reshaping the electromagnetic scattering in the spatial domain. In fact, by manipulating the electromagnetic scattering in the time domain, the visibility of an object can also be reduced. Importantly, unlike previous studies on phase-switched screens and time-varying metasurfaces, where the effect is narrow band due to the dispersive resonance, for microwave frequency range, we introduce a broadband switchable metasurface integrated with p-i-n diodes. The reflection phase of the metasurface can be changed by approximately pi over a fractional bandwidth of 76%. By modulating the metasurface quasirandomly in the time domain, the incident narrow-band signal is spread into a white-noiselike spectrum upon reflection, creating a spectral camouflage. The broadband feature of the proposed time-varying metasurface can provide practical insight for various applications, including radar stealth and ultrawide-band wireless communication.

Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however, its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying metadevice which performs frequency conversion can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both electric and magnetic meta-atoms with independently controlled modulation, and the phase of this modulation is imprinted on the scattered parametric waves, controlling their shapes and directions. We develop a theory which shows how the scattering directionality, phase and conversion efficiency of sidebands can be manipulated almost arbitrarily. We demonstrate novel effects including all-angle beam steering and frequency-multiplexed functionalities at microwave frequencies around 4 GHz, using varactor diodes as tunable elements. We believe that the concept can be extended to other frequency bands, enabling metasurfaces with arbitrary phase pattern that can be dynamically tuned over the complete 2πrange.

Metamaterials are engineered structures designed to interact with electromagnetic radiation. The common understanding in the scientific community is that, a typical metamaterial operates within a particular frequency range that is determined by the metamaterials’ dimensions. In this paper, for the first time to the best of our knowledge, we demonstrate that a metamaterial can be functional in more than one frequency region. We propose an advanced design that can interact with both THz and near-infrared (NIR) frequencies concurrently. Moreover, our novel metamaterial can work independently of the input polarisation in both wavelength regions. We designed and fabricated meander line resonators with 300 nm linewidth distributed over 16.26 μm area and experimentally demonstrate a structure that can simultaneously interact with NIR and THz frequencies with a high miniaturisation factor. This dual-band photonic metamaterials can be used as an advanced device in applications such as sensing, imaging, filtering, modulation, and absorption.

High performance tunable absorbers for terahertz (THz) frequencies will be crucial in advancing applications such as single-pixel imaging and spectroscopy. Metamaterials provide many new possibilities for manipulating electromagnetic waves at the subwavelength scale. Due to the limited response of natural materials to terahertz radiation, metamaterials in this frequency band are of particular interest. The realization of a high-performance tunable (THz) absorber based on microelectromechanical system (MEMS) is challenging, primarily due to the severe mismatch between the actuation range of most MEMS (on the order of 1-10 microns) and THz wavelengths on the order of 100-1000 microns. Based on a metamaterial design that has an electromagnetic response that is extremely position sensitive, we combine meta-atoms with suspended at membranes that can be driven electrostatically. This is demonstrated by using near-field coupling of the meta-atoms to create a substantial change in the resonant frequency. The devices created in this manner are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness ( 1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and with a fast switching speed ( 27 us). In the snap-down state, the resonance shifts by γ >200% of the linewidth (14% of the initial resonance frequency), and the absorption modulation measured at the initial resonance can reach 65%.

Metasurfaces offer a highly flexible platform for controlling the propagation and localization of electromagnetic waves. Due to the relatively large size of commonly used resonators, various undesirable effects including spatial dispersion and spurious diffraction occur, thus limiting the metasurface performance. To overcome these problems, one straightforward approach is to utilize deeply subwavelength metaunits. In contrast to conventional approaches that minimize the resonator size by reshaping the metallic patches, the capacitive gaps are reshaped, an approach which is more robust to material loss, minimizing the problem of overdamping. As an example, a novel design based on interdigital capacitors (meander gap) is introduced with extremely subwavelength gaps for use in the terahertz frequency range. The size of the new resonator can be reduced to below λ/30 in a reflective‐type terahertz metasurface, while maintaining the 2 π phase shift required for full wavefront control. Using an advanced electron‐beam lithography technique, a proof‐of‐concept experiment is performed and a 5 mm × 5 mm beam deflector is fabricated, with the capacitive gaps as small as 300 nm (≈λ/1130). The device performance is characterized using angle‐resolved time‐domain spectroscopy. The study provides useful insight for ultracompact metadevices based on deeply subwavelength metaunits working at terahertz frequencies and beyond.