Shun Cao

The strong coupling between single quantum emitters and resonant optical micro/nanocavities is beneficial for understanding light and matter interactions. Here, we propose a plasmonic nanoantenna placed on a metal film to achieve an ultra-high electric field enhancement in the nanogap and an ultra-small optical mode volume. The strong coupling between a single quantum dot (QD) and the designed structure is investigated in detail by both numerical simulations and theoretical calculations. When a single QD is inserted into the nanogap of the silver nanoantenna, the scattering spectra show a remarkably large splitting and anticrossing behavior of the vacuum Rabi splitting, which can be achieved in the scattering spectra by optimizing the nanoantenna thickness. Our work shows another way to enhance the light/matter interaction at a single quantum emitter limit, which can be useful for many nanophotonic and quantum applications.

The strong coupling between individual quantum emitters and resonant optical micro/nanocavities is beneficial to understand light and matter interactions. Here we propose a plasmonic nanoantenna placed on a metal film to achieve an ultra-high electric field enhancement in the nanogap and ultra-small optical mode volume. The strong coupling between a single quantum dot and the designed structure is investigated in detail by both numerical simulations and theoretical calculations. When a single QD is inserted into the nanogap of the silver nanoantenna, scattering spectra show remarkably large spectral splitting and typical anti-crossing behavior of the vacuum Rabi splitting, which can be realized in the scattering spectra by varying the nanoantenna thickness. Our work shows a possible way to enhance light-matter interaction at a single quantum emitter limit, which can be useful for future quantum and nanophotonic applications.

A patterned structure of monolithic hexagonal boron nitride (hBN) on a glass substrate, which can enhance the emission of the embedded single photon emitters (SPEs), is useful for onchip single-photon sources of high-quality. Here, we design and demonstrate a monolithic hBN metasurface with quasi-bound states in the continuum mode at emission wavelength with ultrahigh Q values to enhance fluorescence emission of SPEs in hBN. Because of ultrahigh electric field enhancement inside the proposed hBN metasurface, an ultrahigh Purcell factor (3.3 × 10⁴) is achieved. In addition, the Purcell factor can also be strongly enhanced in most part of the hBN structure, which makes the hBN metasurface suitable for e.g. monolithic quantum photonics.

Room-temperature strong coupling between quasi-bound states in the continuum (q-BIC) of a silicon-nitride metasurface and excitons in a WS2 monolayer is investigated in detail by both numerical simulations and theoretical calculations. The strong coupling between the q-BIC mode and excitons leads to a remarkable spectral splitting and typical anti-crossing behavior of the Rabi splitting, which can be realized in the absorption spectra by varying the grating thickness and asymmetry parameter of the silicon-nitride metasurface, respectively. In addition, both the linewidth of the q-BIC mode and local electric field enhancement are found to affect the strong coupling, which needs to be considered in detail in q-BIC metasurface designs. This work provides a possible way to enhance light-matter interactions in transition metal dichalcogenides monolayers and pave the way for future quantum and nanophotonic applications.

We proposed a hybrid metamaterial structure based on graphene-silver, which has tunable and efficient light-absorbing performance at mid-infrared regime. It is shown that this model can absorb light effectively with a maximum of 100% at the absorption peak wavelength. In addition, the absorption peak wavelength can be adjusted flexibly by changing parameters, including the chemical potential applied to graphene or other structural parameters of the structure. This nearly perfect absorption capability is attributed to the synergetic effects of localized surface plasmon enhancement of Ag nanoribbon, graphene plasmonics, Metal-Insulator-Graphene mode and Fabry–Perot resonance. This kind of tunable absorber can be used in mid-infrared photodetectors or spectroscopy fields.

Biological research requires wide-field optical imaging techniques with resolution down to the nanometer scale to study the biological process in a sub-cell or single molecular level. To meet this requirement, wide-field structured illumination method (WFSIM) has been extensively studied. The resolution of WFSIM is determined by the period of the optical interference pattern. However, in traditional WFSIM this period is diffraction limited so that pattern having periodicity smaller than 100 nm cannot be generated and as a result achieving an imaging resolution better than 50 nm is a great challenge. Here, we demonstrate a wide-field optical nanoimaging method based on a meta-sandwich structure (MSS) model. It is found that this structure can support standing wave surface plasmons interference pattern with a period of only 31 nm for 532 nm wavelength incident light. Furthermore, the potential application of the MSS for wide-field super-resolution imaging is discussed and the simulation results show an imaging resolution of sub-20 nm can be achieved. The demonstrated method paves a new route for the improvement of the wide field optical nanoimaging, which can be applied by biological researchers to study biological process conducted in cell membrane, such as mass transportation and others.

A gradient permittivity meta-structure (GPMS) model and its application in super-resolution imaging were proposed and discussed in this work. The proposed GPMS consists of alternate metallic and dielectric films with a gradient permittivity which can support surface plasmons (SPs) standing wave interference patterns with a super resolution. By employing the rigorous numerical FDTD simulation method, the GPMS was carefully simulated to find that the period of the SPs interference pattern is only 84 nm for a 532 nm incident light. Furthermore, the potential application of the GPMS for wide-field super-resolution imaging was also discussed and the simulation results show that an imaging resolution of sub−45 nm can be achieved based on the plasmonic structure illumination microscopic method, which means a 5.3-fold improvement on resolution has been achieved in comparison with conventional epifluorescence microscopy. Moreover, besides the super-resolution imaging application, the proposed GPMS model can also be applied for nanolithography and other areas where super resolution patterns are needed.

The near-field enhancement of localized surface plasmon resonance (SPR) in the metal nanoparticles can improve the photocatalytic activity of the semiconductor connected to it. The SPR effect of the Au nanoparticles and the coupling effect of the neighboring Au nanoparticles and the gold film improves the visible-light absorption of TiO2. The simulation result is consistent with the measured absorption spectrum. The photocurrent density of this plasmonic coupling photocatlyst is enhanced significantly compared to the bare TiO2 under the visible light illumination.