Plasmonic nanostructures, with their unique ability to localize electromagnetic fields into nanoscale volumes to create the so-called hot spots, have been widely studied for the enhancement of nonlinear conversion. Various nonlinear optical processes such second-harmonic generation (SHG), third-harmonic generation, or four-wave mixing have been observed in different designed configurations. The SHG process is known to be forbidden in centrosymmetric nanostructures. Thanks to the broken centro-symmetry at the metal surface as well as to the high degree of the asymmetric spatial variation of the inducing electromagnetic fields, strong SHG in noble metals is experimentally observed via properly design.
In this work, we studied the SHG of vertical and planar split ring resonator (SRR) arrays. Via a unique nanofabrication technique, we are able to accurately control the alignment of nano-structures on top of each other and experimentally realize vertical split ring resonators (VSRRs). As VSRRs allow the coupling of both the incident electric and magnetic field to the excitation of magnetic dipole resonance, the induced strong fields confined within two vertical prongs are beneficial for the SHG enhancement. In addition, a better field confinement is achieved for vertical configurations since the localized fields in the planar SRR gaps are inevitably leaked to the underlying substrate. The nonlinear optical measurements showed a 2.6-fold enhancement of SHG nonlinearity for VSRR metasurface compared to their planar counterparts. Through the analysis of multipole decomposition, we found that except for electric dipole, the dominant mode for VSRRs is electric quadrupolar resonance, while that for planar SRRs is magnetic dipole. This work paves the way in increasing the nonlinear transition quantum efficiency and provides a new insight in designing novel nonlinear sources.
Metalenses have great ability in light focusing and can be tailored to exhibit varied functionalities for ultrathin optical applications. Here, we demonstrate a GaN metalens array which can be regarded as a light shaping generator for the structured light generation. The metalens array consists of 60 x 60 metalenses which can project a 42 cm x 42 cm light spots area at the distance of 1.5 M. The distance can be estimated by identifying the deformation of light spot distribution. The advantages of this metadevice is light weight, small, ultrathin, durable and easy to compact with other devices. Our design provides a new avenue for the structured light applications such as distance sensing and 3D environmental construction.
Here we demonstrated a GaN metalens array to project a light spots array which can be a light shape generator in the structure light applications. The advantages of this metadevice is light weight, small, ultrathin, durable and easy to compact with other device. The light spot size is a function with the distance of detector. A metalens array which arranged by the single metalens diameter is 20 μm projected a light spots array whose diameter of single light spot is 2.22 um in average at the distance is 150 cm far away and. Our design provides a new avenue for the structure light application such as distance sensing and 3D environmental construction.
Increasing the nonlinear optical response at nanometer length scale is a very important issue due to the wide applications in various disciplines such as information science, bio-medicine and quantum computation technology. Second harmonic generation (SHG) arising from the metal nanostructures has provide a very powerful tool in studying the surface and interface properties of these materials. The SHG from various kinds of asymmetric geometric configurations such as V and L shape structures, imperfect nano-spheres, metal/insulator/metal multilayer structures, and planar split ring resonators have been proposed. However, all the previous studies in plasmonic nonlinear optical behavior rely on the enhancement of the electric field and seldom considered the magnetic field effect.
In this work, we present a vertical split ring resonator (SRR) based metamaterial to generate SHG. By adopting such a novel structure, both the electric and magnetic field will be significantly enhanced due to the localized surface plasmon resonance, hence the generation of the second-harmonic and its re-emission into the far field are dramatically increased several orders comparing with that of the planar SRR. We simulated and fabricated the reflective type vertical SRR, and optimized the aspect ratio to maximize the SHG signal. We further systematically studied the nonlinear optical response in the vertical SRR dimers and trimers and found that the gap distance between two SRRs plays a very important role in the SHG intensity. This work paves a new way in increasing the nonlinear transition quantum efficiency and provides a new insight in designing new nonlinear sources.
Natural toroidal molecules, such as biomolecules and proteins, possess toroidal dipole moments that are hard to be
detected, which leads to extensive studies of artificial toroidal materials. Recently, toroidal metamaterials have been
widely investigated to enhance toroidal dipole moments while the other multipoles are eliminated due to the spacial
symmetry. In this talk, we will show several cases on the plasmonic toroidal excitation by engineering the near-field
coupling between metamaterials, including their promising applications. In addition, a novel design for a toroidal
metamaterial with engineering anapole mode will also be discussed.