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We propose a compound metallic grating with perpendicular cuts in each slit and investigate its optical transmission property theoretically. The odd and even waveguide modes exhibit different behaviors when the cuts are set asymmetrically in the slits. Particularly, it is shown that the transmission dips of transmission spectrum for this compound periodic structure can be realized alternately by shifting the position of cuts in the slit. The effect of cut size on the phase resonances in the proposed metallic grating is also identified, and the underlying physics is discussed by the simulated field and phase maps.

In this paper, the surface plasmon resonance (SPR) of rectangular cavity is investigated in Ag-Si-SiO2 under near-infrared light incident by finite-difference time-domain (FDTD). Between the surface plasma and the thickness of the silver film, the length of the silver film, the thickness of silicon, and the position of silicon, these relationships will be studied in a rectangular cavity, which is surrounded by silver film, two rectangular nanoscale silicons, and silicon dioxide. The surface plasmon resonance of the RCM is independent of the distance between the two silicons when the transverse silver film length l is fixed and of height d = 10k (k = 1, 2, 3, 4, and 5) nm of rectangular silicon and thickness t (t = 6, 7, 8, 9, 10, 11, and 12 nm) of silver film while the length l = 600 nm. The SPR is a lateral length dependence of silver film. The plasma resonance of the two first-order modes is distributed symmetrically on both sides of the local field in RCM, and it is irrelevant with the position of the vibration mode and the thickness of the silver film. On the basis of the above research, we propose to create a guided-wave resonance that can be directly observed from the normal incidence transmission spectra and electric field distribution. This structure can be used as a highly tunable optical sensitive element that can be tuned with a small change of transverse silver film length. [ABSTRACT FROM AUTHOR]

We propose the idea of a tunable nearly perfect absorber based on graphene metamaterial consisting of a periodically arranged graphene ribbons (bright mode) and the inverse slots in the thin graphene film (dark mode). The absorption peak has a narrow linewidth of 160 nm and the absorbance approaching to 97.12%. The fascinating absorption feature not merely due to plasmonically induced absorption arising from destructive interference between the bright and dark mode but also the metamaterial absorption. We have testified numerically that the electric fields are highly confined inside the slot. The mid-IR absorption spectrum can be dynamically tuned by a small change in the chemical potential of graphene, in addition to varying geometrical parameters. Our paper considers a situation that represents an intermediate plasmonic coupling regime, between near-field and far-field coupling. Such absorber possesses potential for applications in mid-IR nanophotonic devices. [ABSTRACT FROM AUTHOR]

The perfect plasmon-induced absorption (PIA) effect is achieved in a simple plasmonic system, composed of two rectangle cavities side-coupled to the metal-insulator-metal (MIM) waveguide with a barrier. The transmission properties of the system are calculated by the finite-difference time-domain (FDTD) method and theoretically explained by the three-level plasmonic system. More interestingly, the broadband absorption window will be splitted into double windows by adding another rectangle cavity resonator, and the physical mechanism is presented. At the same time, multi-switching effect is also discovered. Undoubtedly, the proposed novel structures have potential application in highly integrated optical circuit and can be simply fabricated. [ABSTRACT FROM AUTHOR]

The phenomenon of plasmon-induced transparency (PIT) is realized a in surface plasmon polariton waveguide at near-infrared frequencies. The right-angled slot and rectangle cavity placed inside one of the metallic claddings are respectively utilized to obtain bright and dark modes in a typical bright-dark mode waveguide. A PIT transmission spectrum of the waveguide is generated due to the destructive interference between the bright and dark modes, and the induced transparency peak can be manipulated by adjusting the size of the bright and dark resonators and the coupling distance between them. Subsequently, spectral splitting based on the PIT structure is studied numerically and analytically. Simulation results indicate that double electromagnetically induced transparency (EIT)-like peaks emerge in the broadband transmission spectrum by adding another rectangle cavity, and the corresponding physical mechanism is presented. Our novel plasmonic structure and the findings pave the way for new design and engineering of highly integrated optical circuit such as nanoscale optical switching, nanosensor, and wavelength-selecting nanostructure. [ABSTRACT FROM AUTHOR]

A numerical and theoretical study is presented on the realization of tunable plasmon-induced transparency (PIT) phenomenon in the three-dimensional patterned graphene nanostrips. The simulation results reveal that the PIT effect is generated due to the excitation of dark mode which can be considered a dipole. The three-level plasmonic system is employed to explain the physical mechanism of the PIT effect. Different from previous reported form (dipole-quadrupole coupling), the proposed is attributed to the dipole-dipole coupling. The PIT effect can be tuned by changing the coupling length between bright and dark mode as well as the Fermi energy of graphene. Our studies provide guidance for fabricating ultra-compact devices in practical application. [ABSTRACT FROM AUTHOR]

In this paper, the graphene ribbon bus waveguide side-coupled a coplanar short graphene strip, constructed on a monolayer graphene with substrates by spatially varying external gates, is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Simulated results exhibit that the outstanding mid-infrared band-stop filtering effect is realized based on the edge mode resonance in the short strip acting as a perfect Fabry-Perot resonator. By changing the locations of gate voltages to vary the size of the short graphene strip, not only the Fabry-Perot resonance mode is tuned effectively but also the original rectangular-loop resonance mode appears. The changes in the coupling distance and substrates are also used for modulating the transmission spectrum. FDTD results are in excellent agreement with the coupled-mode theory (CMT). The simple structure without doubt is a real electrically controlled plasmonic device. Our studies will support the fabrication of planar nano-integrated plasmonic circuits for mid-infrared optical processing. [ABSTRACT FROM AUTHOR]

A narrow-band plasmonic filter based on graphene waveguide with asymmetrical structure is proposed, and the corresponding transmission characteristics are investigated. The asymmetrical structure consists of two sets of five air trenches with different trench sizes. Since the Bragg wavelength could be changed with the length and depth of each air trench, the bandgap (or the passband) of the single set with five short thick air trenches and the passband (or the bandgap) of the single set with five long thin air trenches are overlapped and the cascaded transmission of the two structures is very low in a certain wavelength range. By using the finite-difference time-domain (FDTD) method, a narrow-band transmission peak with 3-dB bandwidth of 0.12 μm could be obtained in the mid-infrared region around 6.9 μm. [ABSTRACT FROM AUTHOR]

A compact plasmonic branch-shaped metal–insulator–metal (MIM) waveguide with a triangular-annular channel is proposed and investigated. The results show that all-band waves can transmit through the structure when it has transmission symmetry. As the symmetry is broken, a typical filtering function is obtained and the transmissivity of the resonance frequency depends on the destroyed degree of symmetry, which results from interference between the two branched surface plasmon polaritons waves (SPPs) propagating along the branch-shaped waveguide. Moreover, the filtering wavelength can be selected by changing the length of the triangular-annular channel. These asymmetric waveguide structures may open up new avenues toward the control of SPPs and the development of filters based on plasmonic designs. [ABSTRACT FROM AUTHOR]

Optical transmission through a double-layer compound metallic grating (DCMG) composed of two identical compound metallic gratings (CMGs) with two subwavelength slits filled with different dielectrics inside each period is investigated by using the finite-difference time-domain method. The results show that the transmission properties of the DCMG are dependent on both the separation G between the two metallic layers and the phase configurations of the electromagnetic waves at the exits of adjacent slits of each layer. When a suitable separation (G ∼ 300 nm) is chosen, for the DCMG a notable transmission peak emerges at a certain wavelength, at which phase resonance appears for the corresponding CMG, while the transmission spectra of the corresponding double-layer simple metallic gratings (DSMGs) with the separation (G ∼ 300 nm) exhibit unexpected transmission suppression in a broad spectral region. When G > 340 nm, the intensity of the transmission around the wavelength for the DCMG gradually decreases down to almost zero as G increases, while the high transmission is nearly maintained for the corresponding DSMGs. [ABSTRACT FROM PUBLISHER]

The transmission of linearly polarized plane wave through cascaded metal films perforated with periodic hole arrays is investigated by using the three-dimensional finite-difference time-domain method. The results show that the transmission spectra can be controlled by changing the longitudinal interval G and/or the lateral displacements Lx and Ly, which are parallel and perpendicular to the polarization direction of the incident light, respectively. The variation in longitudinal interval G results in a redshift or blueshift of the transmission peak due to the coupling of the localized surface plasmon (LSP) modes on two metal layers. The lateral displacement Lx leads to the splitting of the transmission peak, originating from the variation in the coupling manner of LSP modes, while the lateral displacement Ly suppresses the transmission peak. [ABSTRACT FROM AUTHOR]

In this paper, the surface plasmon resonance (SPR) of rectangular cavity is investigated in Ag-Si-SiO2 under near-infrared light incident by finite-difference time-domain (FDTD). Between the surface plasma and the thickness of the silver film, the length of the silver film, the thickness of silicon, and the position of silicon, these relationships will be studied in a rectangular cavity, which is surrounded by silver film, two rectangular nanoscale silicons, and silicon dioxide. The surface plasmon resonance of the RCM is independent of the distance between the two silicons when the transverse silver film length l is fixed and of height d = 10k (k = 1, 2, 3, 4, and 5) nm of rectangular silicon and thickness t (t = 6, 7, 8, 9, 10, 11, and 12 nm) of silver film while the length l = 600 nm. The SPR is a lateral length dependence of silver film. The plasma resonance of the two first-order modes is distributed symmetrically on both sides of the local field in RCM, and it is irrelevant with the position of the vibration mode and the thickness of the silver film. On the basis of the above research, we propose to create a guided-wave resonance that can be directly observed from the normal incidence transmission spectra and electric field distribution. This structure can be used as a highly tunable optical sensitive element that can be tuned with a small change of transverse silver film length. [ABSTRACT FROM AUTHOR]

Abstract: The transmission of p-polarized plane wave through Ag/SiO2 multilayer films perforated with periodic subwavelength air slits is investigated by using the finite-difference time-domain (FDTD) method. The results show that the optical transmission property is mediated by the interference among the propagating coupled-SPP modes along the lateral direction inside the SiO2 layers and the conditions of Fabry–Pérot–like resonance along the longitudinal direction together. When some geometric parameters are suitably initialized, the high transmission peaks can split into more peaks as the functional layer (metal/dielectric/metal sandwich stack) number increases, and the wavelength of the same-order transmission peak exhibits a red shift as the grating period increases. [ABSTRACT FROM AUTHOR]

A novel plasmonic structure, composed of a dipole source and an annular nano-cavity over a nano-slit, is proposed as a surface plasmon polaritons source to enhance the extraordinary optical transmission (EOT) simulated using a finite-difference time-domain (FDTD) method. We find that the annular nano-cavity has an obvious advantage to couple more energy from a dipole source compared with previous EOT configuration. Based on the fact of non-uniform electric field distribution of a dipole source, the transmission through nano-slit is effectively improved by selecting optimized structure parameters. In addition, the transmission spectrum can be well-tuned by adjusting the central angle of the annular nano-cavity, as such, the design holds great promise for its application in EOT-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: We study a transverse magnetic wave propagation in a subwavelength metallic slit which is modified by a perpendicular cut. The surface-plasmon polaritons (SPPs) can be trapped in the perpendicular cut by tuning the length or width of the cut. Moreover, the period of the resonance states corresponds to the difference of the cut''s length ΔL which is 450nm. An analytical solution for the resonance condition of the structure is derived by the cavity theory, which is consistent with the numerical simulation by using the finite difference time domain (FDTD) method. [Copyright &y& Elsevier]