Efficient second-harmonic generation in a lithium niobate metasurface governed by high-Q magnetic toroidal dipole resonances.

Lithium niobate (LN) is an excellent nonlinear optical material due to its large nonlinear coefficient, low loss, and broad optical transparency window. So, it is widely used in the generation of nonlinear harmonics. Magnetic toroidal dipole (MTD) resonance is a special optical resonance mode, which can effectively localize the light field inside the device, thus enhancing the nonlinear effects of the materials.

Active strong coupling of exciton and nanocavity based on GSST-WSe hybrid nanostructures.

The strong coupling between optical resonance microcavity and matter excitations provides a practical path for controlling light-matter interactions. However, conventional microcavity, whose functions are fixed at the fabrication stage, dramatically limits the modulation of light-matter interactions. Here, we investigate the active strong coupling of resonance mode and exciton in GSST-WSe hybrid nanostructures.

Real-time tunable notched waveguide based on voltage controllable ferroelectric resonator.

In the present study, we have devised and conducted an investigation into a real-time tunable notched waveguide, employing a voltage-controllable plasmonic resonator. This plasmonic resonator is meticulously engineered from a ferroelectric substrate featuring a compound multilayer structure, thereby conferring it with the remarkable capability of flexible permittivity control. Furthermore, we have implemented two non-intersecting Archimedean spiral electrodes on the surface of the ferroelectric substrate, dedicated to applying the bias field onto the controllable plasmonic ferroelectric resonator (CPFR).

Second harmonic generation in an anisotropic lithium niobate metasurface governed by quasi-BICs.

Resonant metasurfaces can greatly trap the light fields, so that they are widely used to enhance light-matter interactions at the nanoscale, such as promoting nonlinear effects of materials. Lithium niobate (LN) is an excellent nonlinear optical material and is often employed to generate harmonic signals. In this Letter, we numerically study the second harmonic generation (SHG) characteristics of the LN metasurface based on the quasi-bound states in the continuum (QBIC).

Strong coupling of excitons and electric/magnetic toroidal dipole modes in perovskite metasurfaces.

Effective manipulation of the interactions between light and matter is crucial for the advancement of various high-performance optoelectronic devices. It is noted that the toroidal dipole resonance refers to an electromagnetic excitation that exists beyond the conventional understanding of electric and magnetic multipoles, which shows great potential for enhancing light-matter interactions. In this work, we investigate the strong coupling properties of electric toroidal dipole (ETD) and magnetic toroidal dipole (MTD) with excitons in (PEA)PbI perovskite metasurfaces.

Toroidal Dipole BIC-Driven Highly Robust Perfect Absorption with a Graphene-Loaded Metasurface.

Achieving perfect absorption in few-layer two-dimensional (2D) materials plays a crucial role in applications such as optoelectronics and sensing. However, the underlying mechanisms of all reported works imply a strongly inherent dependence of the central wavelength on the structural parameters. Here, we propose a structure-parameter-deviation immune method for achieving perfect absorption at any desired wavelength by harnessing the toroidal dipole-bound state in the continuum (TD BIC).

Ultrahigh-Q guided mode resonances in an All-dielectric metasurface.

High quality(Q) factor optical resonators are indispensable for many photonic devices. While very large Q-factors can be obtained theoretically in guided-mode settings, free-space implementations suffer from various limitations on the narrowest linewidth in real experiments. Here, we propose a simple strategy to enable ultrahigh-Q guided-mode resonances by introducing a patterned perturbation layer on top of a multilayer-waveguide system.

Active optical modulation of quasi-BICs in Si-VO hybrid metasurfaces.

Active optical modulation breaks the limitation of a passive device, providing a new, to the best of our knowledge, alternative to achieve high-performance optical devices. The phase-change material vanadium dioxide (VO) plays an important role in the active device due to its unique reversible phase transition. In this work, we numerically investigate the optical modulation in resonant Si-VO hybrid metasurfaces.

Active quasi-BIC metasurfaces assisted by epsilon-near-zero materials.

Active devices play a critical role in modern electromagnetic and photonics systems. To date, the epsilon ()-near-zero (ENZ) is usually integrated with the low Q-factor resonant metasurface to achieve active devices, and enhance the light-matter interaction significantly at the nanoscale. However, the low Q-factor resonance may limit the optical modulation.

Quasi-bound states in the continuum with a stable resonance wavelength in dimer dielectric metasurfaces.

Symmetry-protected bound states in the continuum (SP-BICs) are one of the most intensively studied BICs. Typically, SP-BICs must be converted into quasi-BICs (QBICs) by breaking the unit cell's symmetry so that they can be accessed by the external excitation. The symmetry-broken usually results in a varied resonance wavelength of QBICs which are also highly sensitive to the asymmetry parameters.

Quasi-symmetry-protected BICs in a double-notched silicon nanodisk metasurface.

Bound states in the continuum (BICs) hold great promise in enhancing light-matter interaction as they have an infinite Q-factor. To date, the symmetry-protected BIC (SP-BIC) is one of the most intensively studied BICs because it is easily found in a dielectric metasurface satisfying certain group symmetry. To convert SP-BICs into quasi-BICs (QBICs), structural symmetry shall be broken so that external excitation can access them.

Strong light-matter interactions of exciton in bulk WS and a toroidal dipole resonance.

Exciton-polaritonic states are generated by strong interactions between photons and excitons in nanocavities. Bulk transition metal dichalcogenides (TMDCs) host excitons with a large binding energy at room temperature, and thus are regarded as an ideal platform for realizing exciton-polaritons. In this work, we investigate the strong coupling properties between high-Q toroidal dipole (TD) resonance and bulk WS excitons in a hybrid metasurface, consisting of SiN nanodisk arrays with embedded WS.

Tunable light trapping in the graphene metasurface.

Graphene metasurfaces based on surface plasmon resonance can greatly enhance the interaction between light and matter at the nanoscale. At present, the resonance of graphene metasurfaces is widely used to enhance the absorption of atomic layer graphene, but little work has focused on the light field trapping capabilities it brings. In this paper, we numerically study the light trapping and manipulation of an asymmetric graphene metasurface.

Bound states in the continuum supported by silicon oligomer metasurfaces.

Oligomer metasurfaces have attracted a lot of attention in recent years because of their ability to drive strong resonance effects. In this work, by perturbing the symmetry of the structure, we find that there are a large number of resonance modes in the oligomer metasurfaces associated with the optical bound states in the continuum (BICs) near the communication wavelength. When the positions of two nanodisks of the hexamer oligomers are moved along the x- or y-directions at the same time, the mirror symmetry is broken, and an electric quadrupole BIC and three magnetic dipole BICs are excited.

Manipulating Optical Scattering of Quasi-BIC in Dielectric Metasurface with Off-Center Hole.

Bound states in the continuum (BICs) correspond to a particular leaky mode with an infinitely large quality-factor (Q-factor) located within the continuum spectrum. To date, most of the research work reported focuses on the BIC-enhanced light matter interaction due to its extreme near-field confinement. Little attention has been paid to the scattering properties of the BIC mode.

Active magnetic dipole emission by the GeSbTe nanodisk.

Active light manipulation plays a critical role in nanophotonics. In this Letter, we investigate the modulation properties of magnetic dipole (MD) emission based on the phase change material hollow nanodisk (GST-HND). The results show that the amorphous GST-HND supports a strong MD response with a radiative decay enhancement of 282 times and quantum efficiency of 100%.

Tailoring anisotropic absorption in a borophene-based structure via critical coupling.

The research of two-dimensional (2D) materials with atomic-scale thicknesses and unique optical properties has become a frontier in photonics and electronics. Borophene, a newly reported 2D material, provides a novel building block for nanoscale materials and devices. We present a simple borophene-based absorption structure to boost the light-borophene interaction via critical coupling in the visible wavelengths.

Gain-assisted critical coupling for enhanced optical absorption in graphene.

Enhanced optical absorption in two-dimensional (2D) materials has recently moved into the focus of nanophotonics research. In this work, we present a gain-assisted method to achieve critical coupling and demonstrate the maximum absorption in undoped monolayer graphene in the near-infrared. In a two-port system composed of photonic crystal slab loaded with graphene, the gain medium is introduced to adjust the dissipative rate to match the radiation rate for the critical coupling, which is accessible without changing the original structural geometry.

Thermochromic VO-SiOcomposite coating from ammonium citrato-oxovanadate(IV).

Vanadium dioxide (VO) coating plays an important role in energy saving and environmental protection due to its unique reversible phase transition. To solve the daylighting issue of VOcoating, a VO(M)-silicon dioxide (SiO) composite coating is fabricated from ammonium citrato-oxovanadate(IV) by a SiO-assisted coating method. The VO(M)-SiOcomposite coating possesses excellent thermochromic properties that have produced varying results, i.

Polarization-independent toroidal dipole resonances driven by symmetry-protected BIC in ultraviolet region.

Optical resonances have gained great attention in nanophotonics attributing to their large enhancement of local field. In this work, we investigate polarization-independent toroidal dipole responses governed by bound state in the continuum (BIC) in the ultraviolet region. By introducing symmetry breaking, an asymmetric dielectric nanohole array is employed to excite two symmetry-protected BICs.

Optical radiation manipulation of Si-GeSbTe hybrid metasurfaces.

Active optical metadevices have attracted growing interest for the use in nanophotonics owing to their flexible control of optics. In this work, by introducing the phase-changing material GeSbTe (GST), which exhibits remarkably different optical properties in different crystalline states, we investigate the active optical radiation manipulation of a resonant silicon metasurface. A designed double-nanodisk array supports a strong toroidal dipole excitation and an obvious electric dipole response.

Black phosphorus-based anisotropic absorption structure in the mid-infrared.

Black phosphorus (BP), an emerging two-dimensional (2D) material with intriguing optical properties, forms a promising building block in optical and photonic devices. In this work, we propose a simple structure composed of a monolayer BP sandwiched by polymer and dielectric materials with low index contrast, and numerically demonstrate the perfect absorption mechanism via the critical coupling of guided resonances in the mid-infrared. Due to the inherent in-plane anisotropic feature of BP, the proposed structure exhibits highly polarization-dependent absorption characteristics, i.

Fano-resonant silicon photonic crystal slab for efficient third-harmonic generation.

Strong light-matter interactions in resonant photonic nanostructures open up opportunities for enhancing nonlinear responses. In this work, by applying Fano resonances, we experimentally demonstrate efficient third-harmonic generation (THG) obtained with 2D silicon photonic crystal slabs (PCSs) thanks to the field enhancement in the dielectric layer. A 160-fold enhancement of THG is observed in the silicon PCS compared to the unpatterned silicon film.