Search

Owe to the ability of supporting propagating surface plasmons, silver nanowire can be decent candidate as optical nanoantenna to modulate the polarization property of nano-emitters. Here, we created a quantum dots and silver nanowire coupling system to implement the controllable polarization dependence of this antenna effect. Several basic modes are mainly explored with both positive and negative excitation and observation directions. For the contrast excitation directions, both the center and the end fluorescence spots have reverse polarization dependence characterizations. While the controllable polarization dependence only appears at the center spot for the different observation angles. Based on these modes, diverse polarization dependence properties can be extended flexibly. The reasons for the phenomena are explained using the theoretical simulation. The numerical calculation shows the silver nanowire can act both optical receiving antenna and transmitting antenna in this process. Achieving on the controllable polarization dependence, our results are useful in the investigation about the coupling of nano-emitters and optical antenna. • The controllable polarization dependence is implemented in our coupling system. • Two modes with reverse excitation and observation are explored experimentally. • Reverse dependence for contrast excitation arises at both the center and the end. • The controllable dependence appears at the center for reverse observation angles. • The reasons for the phenomena are explained using the theoretical simulation. [ABSTRACT FROM AUTHOR]

As one of the indispensable instruments in many fields, optical tweezers are extensively utilized in micromanipulation. Vortex beams and diverse structured light fields make multi-trap optical tweezers possible. Here, the radiation forces of Laguerre-Gaussian (LG) composite vortex beams exerting on a Rayleigh dielectric particle are investigated. Our results show that the multi-trap optical tweezers can be produced by the Laguerre-Gaussian composite vortex beams, which can trap the particles with both high and low refractive indices in the focus plane at multiple positions. Moreover, by changing the orbital angular momentum (OAM) quantum numbers and energy ratios of the Laguerre-Gaussian modes participated in the superposition, the quantities of the optical traps and the distances between multiple traps can be conveniently adjusted. Our beams can be generated by several methods, which provides more convenience for the creation of multiple optical traps. The results presented in this work are potential in optical micromanipulation, as well as other applications in biology and chemistry. • The radiation forces of Laguerre-Gaussian composite vortex beams are investigated. • The both high- and low-index particles can be trapped at multiple positions. • The quantities and the distributions of the multiple traps can be adjusted. [ABSTRACT FROM AUTHOR]

We investigate for the first time the effects of a bar on the non-periodic waveguide system, which consists of a wide gap metal–insulator–metal (MIM) structure intermediately connecting with a narrow gap MIM waveguide, by means of the finite element method. Simulation results show that the introduction of a metallic bar enriches the transmission spectra. As the bar has more influence on the electric (magnetic) field in the wide gap MIM waveguide, the transmission peaks exhibit red-shift (blue-shift), in comparison with the corresponding resonant wavelength without the bar. These phenomena can be well explained by the surface charge and current model. In addition, we propose a fitting formula to reveal the relationship between the resonant wavelength and the parameters of the structure. All of the calculated results match the model and the new fitting formula very well. Moreover, when the symmetry of the structure is breaking, the anti-symmetric waveguide mode of the wide gap MIM waveguide is excited. Then the interference of the narrow trapped resonance and the broad Lorentzian-like resonance based on different waveguide modes (anti-symmetric mode and the symmetric mode) gives rise to a Fano resonance in the broken plasmonic resonator. The mechanism based on different waveguide modes paves a new route to realizing Fano resonance in the plasmonic waveguide system. The utilization of the fitting formula and anti-symmetric mode in the MIM waveguide provides a new possibility for designing high-performance plasmonic devices. [ABSTRACT FROM AUTHOR]

The three-mode coupling among excitons–surface plasmon(SP)–excitons has attracted extensive attention owing to its richer modulation capability compared to traditional two-mode coupling. However, the coupling mechanism of middle hybrid state in three-mode systems has not been clear. Here, we develop a full quantum theory based on the Jaynes–Cummings model to investigate the properties of middle plexciton branch (MPB) in excitons–SP–excitons system. The calculated scattering spectrum includes three plexciton branches, which shows that the MPB has the narrowest linewidth and lowest peak amplitude compared to the other two branches. The derived Hopfield coefficients demonstrate that the narrowest linewidth of MPB is due to its low SP fraction compared to that of excitons, which is different from the fractions of SP and excitons for the other two branches. The calculated results indicate that MPB peak amplitude is lowest because the detuning between two excitons is smaller than the coupling coefficient g, and MPB has the lowest population compared with those of the other two branches. Additionally, to verify our theory, we design an Au nanorod coated with two layers of J-aggregate nanoshells by the finite-difference time-domain (FDTD) simulation which results accord well with our theory. Our work has wide applications in quantum optical devices, quantum information, and quantum computing. • In the scattering spectrum, the middle plexciton branch(MPB) has the narrowest linewidth and lowest peak amplitude. • The Hopfield coefficients demonstrate that the surface plasmon(SP) fraction in MPB is low. • The MPB peak amplitude depends on the detuning between two excitons and the coupling coefficient g. • The MPB has the lowest population compared to those of the other two branches. [ABSTRACT FROM AUTHOR]

We proposed a plasmonic nanosensor based on Fano resonance in the symmetric and asymmetric plasmonic waveguide system, which comprises with a rectangular cavity and two slot cavities with the metal-dielectric-metal waveguide. Simulation results show that by symmetric/asymmetry rectangular cavity and regulating the rectangular cavity coupling with slot cavities, different waveguide modes can be excited. Due to the interaction of the waveguide mode, the transmission spectra possess single, double or multiple sharp asymmetrical profiles. Because of the different origins, these Fano resonances exhibit different dependence on the parameters of the structure and can be easily tuned. These characteristics offer flexibility to design the device. This nanosensor yields a sensitivity of ∼800 nm/RIU and a figure of merit of about ∼1.35×10 4 , which can find widely applications in the plasmonic nano-sensing area. [ABSTRACT FROM AUTHOR]

Abstract: We investigate a plasmonic waveguide system using a 2-dimension finite element method, which consists of a metal-insulator-metal waveguide coupled with a stub resonator and a baffle. Numerical simulations results show that the sharp and asymmetric Fano-line shapes can be created by placing a baffle into the waveguide, and the main dependent factors of Fano-like spectra response are discussed. Based on the above results, we design three kinds of plasmonic waveguides with possible applications in wavelength demultiplexing. An analytic model based on the transfer matrix formalism is utilized to describe and explain this phenomenon. These results could be applied for developing ultra-compact wavelength division multiplexing devices in highly all-optical integration system. [Copyright &y& Elsevier]

In this paper, the strong exciton–plasmon couplings dependent on two localized modes are numerically and theoretically investigated in cuboid dielectric–metal core–shell resonators. For different resonance wavelengths, the electric fields of different modes can be highly localized in the dielectric gap layer, bringing about very small mode volumes. Through the active control of core–shell cavity parameters, the Rabi splitting and the anti-crossing dispersion are observed in the extinction spectrum, confirming the realization of strong coupling Both the multimode interference coupled mode theory and the Bloch equation are applied to explain the strong coupling in this system. After replacing the shell metal from silver to gold, the large red shift of resonance peaks exactly makes the high order mode strongly coupled with the same J-aggregate molecules, thus inducing slight spatial changes and reducing the required minimum number of the coupled excitons. [ABSTRACT FROM AUTHOR]