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Monolayered transition metal dichalcogenides (TMDs) are one kind of hexagonal 2D semiconductors with a direct bandgap structure. Due to the property of natural broken inversion symmetry in the lattice, the strong spin–orbit coupling of electrons in TMDs can induce degenerate levels with antiparallel spins in K and K′ valleys, which selectively respond with external light excitations. Surface plasmon resonance with efficient electromagnetic enhancement and near‐field coupling provides excellent potential opportunities to modulate valley emission of TMDs. Efforts have been devoted to investigating the interaction principles and applications of this research field. This review focuses on plasmonic modulation of valleytronic emission in TMDs with surface plasmon polaritons (SPP) and localized surface plasmons (LSP) based on different modulation principles, respectively, and discusses possible research directions for future device applications. [ABSTRACT FROM AUTHOR]

Spontaneous emission can be altered by external electromagnetic environment with the bridge of local density of optical states. Microcavities have been widely integrated to accelerate the irreversible spontaneous decay, known as the Purcell effect. However, the Purcell effect breaks down in the strong coupling regime, where the light‐matter interaction is not a perturbation to Fermi's golden rule. Here, it is found that the emission intensity of plasmon–exciton polaritons is asymmetrically dependent on the spectral detuning, confirming the collapse of Purcell effect in strongly coupled systems. Ultrafast nonradiative decays of polaritons play a significant role in revealing the polariton emission intensity. The nonradiative effect is not affected by the coherent energy exchange since final states of nonradiative decays are optically dark and decoupled from Rabi oscillations. Moreover, the nonradiative effect is still valid under intermediate coupling and agrees with the Purcell effect, which suggests its universality at a variety of coupling regimes. This study opens up a successful approach to investigate spontaneous emission in cavity quantum electrodynamics, which is insightful to photonic and opto‐electronic applications based on exciton‐polaritons. [ABSTRACT FROM AUTHOR]

Metasurfaces are made of two-dimensional arrays of subwavelength nanostructures that form a spatially varying optical response, to control the wave fronts of optical waves. As the feature size of its constituent materials is nanoscale, investigation of the light-nanostructure interactions in the near field is critical for understanding the novel properties of metasurfaces. Here, we used a scanning near-field optical microscope (SNOM) to observe the near-field distribution of surface plasmon polaritons (SPPs) from a ring-shaped metasurface under illumination of circularly polarized light. It was found that with an additional degree of freedom of the geometric phase provided by the regularly arranged metamolecules, control over the near-field interference of the SPPs can be achieved, which is governed by the metasurface geometric symmetry that can be tuned by its topological charge. Meanwhile, the planar chiral character of the metamolecules exerts a deep influence on the near-field interference patterns. Our results can pave the way for active control of SPP propagation in near fields and have potential applications in highly integrated optical communication systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose and simulate the surface plasmon polariton nanofocusing process by using Finite-difference Time-domain (FDTD) method. The maximum enhancement factor at the taper end area is optimized with different wavelength of the excitation laser. With the advantage of SNOM, the SPP nanofocusing is experimentally observed by illuminating the tapered CdS nanoribbon deposited on the Ag film. The SPP dispersion is used to predict the optimal taper angles of the structure. As the emission of the focused SPP at the taper end, the proposed plasmonic structure can be severed as a light nanosource emitter in the future optical integrated circuits. [ABSTRACT FROM AUTHOR]

The surface plasmon polariton (SPP) coupling and enhancement in silver nanowire–nanoantenna structure is proposed and simulated by using finite difference time domain method. The results demonstrate that three-arm antenna can effectively enhance the coupling efficiency at the incident end and the SPP field intensity at the emission end. The enhancement factor, which is defined as the ratio of the SPP field intensity at the emission end with and without the three-arm antenna, for the various antenna arm lengths and incident wavelengths under different incident angles are calculated. The suggested structure can be served as an enhanced plasmonic waveguide for the nanophotonic and plasmonic circuits in the future. [ABSTRACT FROM AUTHOR]