Helicity dependent directional surface plasmon polariton excitation using a metasurface with interfacial phase discontinuity

Surface plasmon polaritons(SPPs)have been widely exploited in various scientific communities,ranging from physics,chemistry to biology,due to the strong confinement of light to the metal surface.For many applications,it is important that the free space photon can be coupled to SPPs in a controllable manner.In this Letter,we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization-dependent SPP unidirectional excitation at normal incidence.Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light.This approach,in conjunction with dynamic polarization modulation techniques,opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities.

Fano resonance boosted cascaded optical field enhancement in a plasmonic nanoparticle-in-cavity nanoantenna array and its SERS application

Cascaded optical field enhancement(CFE)can be realized in some specially designed multiscale plasmonic nanostructures,in which the generation of extremely strong fields at nanoscale volume is crucial for many applications,for example,surface-enhanced Raman spectroscopy(SERS).In this paper,we propose a strategy for realizing a high-quality plasmonic nanoparticle-in-cavity(PIC)nanoantenna array,in which strong coupling between a nanoparticle(NP)dark mode with a high-order nanocavity bright mode can produce strong Fano resonance at the target wavelength.The Fano resonance can effectively boost the CFE in a PIC.A cost-effective and reliable nanofabrication method is developed using room temperature nanoimprinting lithography to manufacture high-quality PIC arrays.This technique guarantees the generation of only one gold NP at the bottom of each nanocavity,which is crucial for the generation of the expected CFE.To demonstrate the performance and application of the PIC array,the PIC array is employed as an active SERS substrate for detecting 4-aminothiophenol molecules.An experimental SERS enhancement factor of 2×10^(7) is obtained,which verifies the field enhancement and the potential of this device.

Silicon nitride-based Kerr frequency combs and applications in metrology

Kerr frequency combs have been attracting significant interest due to their rich physics and broad applications in metrology,microwave photonics,and telecommunications.In this review,we first introduce the fundamental physics,master equations,simulation methods,and dynamic process of Kerr frequency combs.We then analyze the most promising material platform for realizing Kerr frequency combs—silicon nitride on insulator(SNOI)in comparison with other material platforms.Moreover,we discuss the fabrication methods,process optimization as well as tuning and measurement schemes of SNOI-based Kerr frequency combs.Furthermore,we highlight several emerging applications of Kerr frequency combs in metrology,including spectroscopy,ranging,and timing.Finally,we summarize this review and envision the future development of chip-scale Kerr frequency combs from the viewpoint of theory,material platforms,and tuning methods.

Bi-channel near-and far-field optical vortex generator based on a single plasmonic metasurface

With the recent development of the metasurface,generating an optical vortex in optical far or near fields is realized in various ways.However,to generate vortices in both the near and far fields simultaneously is still a challenge,although it has great potential in the future compact and versatile photonic system.Here,a bi-channel optical vortex generator in both the near and far fields is proposed and demonstrated within a single metasurface,where the surface plasmon vortex and the far-field optical vortex can be simultancously generated under circularly polarized light.The ability of generating vortices with arbitrary topological charges is experimentally demon-strated,which agrces well with simulations.This approach provides great freedom to integrate different vortex generators in a single device and ofers new opprtunities for integrated optical communications,trapping,and other related fields.

Transient Superdiffusion of Energetic Carriers in Transition Metal Dichalcogenides Visualized by Ultrafast Pump-Probe Microscopy

Because of the strong Coulomb interaction and quantum confinement effect,2-dimensional transitionmetal dichalcogenides possess a stable excitonic population.To realize excitonic device applications,such as excitonic circuits,switches,and transistors,it is of paramount importance for understanding the optical properties of transition metal dichalcogenides.Furthermore,the strong quantum confinement in 2-dimensional space introduces exotic properties,such as enhanced phonon bottlenecking effect,many-body interaction of excitons,and ultrafast nonequilibrium exciton-exciton annihilation.Exciton diffusion is the primary energy dissipation process and a working horse in excitonic devices.In this work,we investigated time-resolved exciton propagation in monolayer semiconductors of wSe_(2),MowSe_(2),and MoSe_(2),with a home-built femtosecond pump-probe microscope.We observed ultrafast exciton expansion behavior with an equivalent diffusivity of up to 502 cm^(2)s^(-1)at the initial delay time,followed by a slow linear dffusive regime(20.9 cm^(2)s^(-1))in the monolayer WSe_(2).The fast expansion behavior is attributed to energetic carrier-dominated superdiffusive behavior.We found that in the monolayers MowSe_(2)and MoSe_(2),the energetic carrier-induced exciton expansion is much more effective,with diffusivity up to 668 and 2295 cm^(2)s^(-1),respectively.However,the"cold"exciton transport is trap limited in MowSe_(2)and MoSe_(2),leading to negative diffusion behavior at later time.Our findings are helpful to better understand the ultrafast nonlinear diffusive behavior in strongly quantum-confined systems.It may be harnessed to break the limit of conventional slow diffusion of excitons for advancing more efficient and ultrafast optoelectronicdevices.