Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality

The realization of lossless metasurfaces with true chirality crucially requires the fabrication of three-dimensional structures,constraining experimental feasibility and hampering practical implementations.Even though the threedimensional assembly of metallic nanostructures has been demonstrated previously,the resulting plasmonic resonances suffer from high intrinsic and radiative losses.The concept of photonic bound states in the continuum(BICs)is instrumental for tailoring radiative losses in diverse geometries,especially when implemented using lossless dielectrics,but applications have so far been limited to planar structures.Here,we introduce a novel nanofabrication approach to unlock the height of individual resonators within all-dielectric metasurfaces as an accessible parameter for the efficient control of resonance features and nanophotonic functionalities.In particular,we realize out-of-plane symmetry breaking in quasi-BIC metasurfaces and leverage this design degree of freedom to demonstrate an optical all-dielectric quasi-BIC metasurface with maximum intrinsic chirality that responds selectively to light of a particular circular polarization depending on the structural handedness.Our experimental results not only open a new paradigm for all-dielectric BICs and chiral nanophotonics,but also promise advances in the realization of efficient generation of optical angular momentum,holographic metasurfaces,and parity-time symmetry-broken optical systems.

Double-layer graphene for enhanced tunable infrared plasmonics

Graphene is emerging as a promising material for photonic applications owing to its unique optoelectronic properties.Graphene supports tunable,long-lived and extremely confined plasmons that have great potential for applications such as biosensing and optical communications.However,in order to excite plasmonic resonances in graphene,this material requires a high doping level,which is challenging to achieve without degrading carrier mobility and stability.Here,we demonstrate that the infrared plasmonic response of a graphene multilayer stack is analogous to that of a highly doped single layer of graphene,preserving mobility and supporting plasmonic resonances with higher oscillator strength than previously explored single-layer devices.Particularly,we find that the optically equivalent carrier density in multilayer graphene is larger than the sum of those in the individual layers.Furthermore,electrostatic biasing in multilayer graphene is enhanced with respect to single layer due to the redistribution of carriers over different layers,thus extending the spectral tuning range of the plasmonic structure.The superior effective doping and improved tunability of multilayer graphene stacks should enable a plethora of future infrared plasmonic devices with high optical performance and wide tunability.

DNA-assembled bimetallic plasmonic nanosensors

Plasmonic hybrid nanomaterials are highly desirable in advanced sensing applications.Different components in these materials undertake distinct roles and work collectively.One material component may act as an efficient light concentrator and optical probe,whereas another provides specific chemical or biological functionality.In this work,we present DNA-assembled bimetallic plasmonic nanostructures and demonstrate their application for the all-optical detection of hydrogen.Gold(Au)nanorods are functionalized with DNA strands,which serve both as linkers and seeding sites for the growth of palladium(Pd)nanocrystals and facilitate reliable positioning of Pd satellites around an Au nanorod at an ultrashort spacing in the nanometer range.Dark-field scattering spectra of single Au–DNA–Pd nanorods were recorded during controlled cycles of hydrogen gas exposure,and an unambiguous concentration-dependent optical response was observed.Our method enables,for the first time,the all-optical detection of hydrogen-induced phase-change processes in sub-5-nm Pd nanocrystals at the single-antenna level.By substituting the Pd satellites with other functional materials,our sensor platform can be extended to plasmonic sensing of a multitude of chemical and biological reagents,both in liquid and gaseous phases.

Tunable structural colors on display

Structural coloration takes inspiration from the bright hues found in nature to control the reflection and transmission of light from artificially structured materials.Combining them with active electrical tuning heralds breakthrough applications in optical displays.