Graphene-based and metal-based surface plasmon polariton (SPP) waveguides have attracted intense research interest because they can be used as basic components to propagate electromagnetic (EM) waves in future optical integrated systems. We propose a directional coupler, which can couple EM energy from a multilayer-graphene-based cylindrical long-range SPP waveguide to a metal-based cylindrical hybrid SPP waveguide in the mid-infrared range. This coupler exhibits relatively low coupling length, high coupling efficiency, low insertion loss, and high extinction ratio after adjustment of the wave vector mismatch of the two waveguides. Moreover, this coupler is tolerant to practical fabrication errors like misalignment of graphene layres, and can effectively work in the range of Fermi energy E_f > 0.6 eV when the mobility of graphene varies from 10000 to 800 cm²/Vs. Hence, the coupler offers potential applications in signal routing and information exchange between graphene-based and metal-based SPP waveguides in photonic integrated circuits.

A long-range surface plasmon polariton (SPP) waveguide, composed of double-layer graphene, can be pivotal in transferring and handling mid-infrared electromagnetic waves. However, one of the key challenges for this type of waveguide is how to excite the SPP modes through an incident light beam. In this study, our proposed design of a novel grating, consisting of a graphene-based cylindrical long-range SPP waveguide array, successfully addresses this issue using finite-difference time-domain simulations. The results show that two types of symmetric coupling modes (SCMs) are excited through a normal incident light. The transmission characteristics of the two SCMs can be manipulated by changing the interaction of the double-layer gratings of graphene as well as by varying various parameters of the device. Similarly, four SCMs can be excited and controlled by an oblique incident light because this light source is equivalent to two orthogonal beams of light. Furthermore, this grating can be utilized in the fabrication of mid-infrared optical devices, such as filters and refractive index sensors. This grating, with double-layer graphene arrays, has the potential to excite and manipulate the mid-infrared electromagnetic waves in future photonic integrated circuits.

In this work, we demonstrate that optical pulling forces (OPFs) can be induced by a hybrid dimer consisting of a Si nanoparticle (NP) and a coated nanoparticle with a gain core and Au shell under normal plane wave illumination. Analytical theory reveals that the underlying physical mechanism relies on interactions between the electric dipole (ED) modes excited in the NPs. As compared with the individual NP, it is found that the magnitude of optical force can be enlarged by almost three orders for the Si NP and one order for the coated gain NP in the coupled dimer. In addition, we find that the OPFs exerted on the NPs are heavily dependent on the gain level of the core materials, the incident polarization angle and the sizes of the NPs. More interestingly, we find that the OPF can also be exerted on a trimer system consisting of two identical Si NPs and a coated NP arranged in a line. The related results could be used to propose a versatile platform for manipulating NPs.

Cylindrical waveguides have a wide range of applications in photonic integrated circuits because of lower transmission losses. This paper proposes a directional coupler composed of a cylindrical silicon nanowire waveguide and a metal-based cylindrical hybrid plasmon waveguide. The coupling characteristics of the coupler are analyzed theoretically and are also simulated using the finite-difference time-domain method. The results show that the coupler can operate effectively with a relatively short coupling length, displaying low insertion loss, and a high coupling efficiency and extinction ratio. This study also shows how the TM mode in the plasmon waveguide can be excited with the TE mode of the dielectric waveguide. This directional coupler has a potential application in signal exchanging and mode switching between the dielectric and plasmon waveguides in photonic integrated circuits.

In the present work, we theoretically and numerically investigate the near field optical binding force on Au–Ag nanorod heterodimers, which can support the electrical dipole–dipole type Fano resonance, under a normally plane wave or polarized laser beam. The numerical results show that the optical binding force between the heterodimer can be reversed near the position of the Fano dip when the incident wave is polarized along the dimer axis, indicating an attractive to repulsive transition. Compared with the Au–Ag heterodimer, the Au and Ag homodimers with the same material show no repulsive binding force. Using the multipole decomposition method, we find that the sign of optical binding force is completely determined by the phase difference of the separated electric dipole plasmon modes excited in the different particles, which can be strongly affected by the wavelength of the incident wave. In addition, we demonstrate the effects of three geometrical parameters (including the length, radius, and gap of the heterodimer) on the Fano-mediated optical binding force in detail. Finally, the numerical results indicate that the reversal of attractive and repulsive forces can also be obtained when the heterodimer is illuminated with a laser beam. Our findings are important for not only a deep understanding of plasmonic-mediated optical binding force but also stable optical manipulation of the plasmonic particles.