Characteristic Study Of Couping And Transmission Based On Surface Plasmon In Several Typical Structures

Surface Plasmon Polaritons is the excited state of evanescent wave, which is localized on the surface of a metal by the interaction of free-electrons with photons.Recent years,the traditional medium integrated optic components have a bottleneck in miniaturization and integration for the diffraction limit.The Surface Plasmon could highly confine the energy at the surface between the metal and dielectric. Through the structural modulation of the subwavelength on the surface of nanoscale,it can control wave field along the surface,particularly its interaction with light.It has tremendous potential applications in the future nanotechnology areas,such as nano-photonic devices,integrated optoelectronic chips and so on,thus it has attracted the broad attention. In this paper,by means of ISE TCAD software,the research focused on simulating three kinds of basic metal structures and the grooved structure embedded a strip cavity based on Surface Plasmon.In the thesis,by using different structures to excite Surface Plasmon, there have got three kinds of structure,a metal with infinite thickness, finite thickness and Metal-Insulator-Metal.With respect to the understanding of using any structure to excite Surface Plasmon by the dispersion curve,the wave vector is added.The thesis uses end-fire coupling to increase the wave vector.There are two kinds ofω^±mode in structure of a metal with finite thickness and Metal-Insulator-Metal. When the metal thickness of a metal with finite thickness increases and the Insulator thickness of Metal-Insulator-Metal,it is equal to a metal with infinite thickness.Such results are expecting,in addition,by using the resonance modes of the symmetry and anti-symmetry to excite difference result of Surface Plasmon.Exactly how the cavity length affects tunneling frequencies is examined first.Figure l plots the transmission coefficient contours of the cavity-embedded silver film as functions of both cavity length and incident wave frequency.Figure 2 presents the tunneling frequencies of the grooved film without the embedded cavity split into lower and higher frequencies around the absorption frequency of the grooved structure.Fig.2.Contour plot of transmission coefficients versus both cavity length and incident wave frequency for a grooved silver film with an embedded cavity The observed changes in tunneling frequencies(Fig.2) are investigated by examining the magnetic field patterns in the grooves and the cavity. Figures 3 and 4 show the distributions of magnetic field Hz at the frequencies of the first and third transmission maxima,respectively,for a grooved silver film with an embedded 90-nm-long cavity.The magnetic fields in the groove and nearby end of the cavity have the opposite(Fig. 3) and the same(Fig.4) polarities.The tunneling effects are determined by both resonant tunneling through the gap between the groove and the cavity and the cavity itself.The groove and the cavity form a complete resonant restructure and,hence,this Letter refers to these two transmission maxima as the coupling mode.The field patterns in the cavity are attributed to the formation of standing waves of coupled SPs.The coupled SPs experience a phase angle change of nÏ€from one end of the cavity to the other end,where n is the number of nodes of the coupled SPs in the cavity.Thus,the resonant frequencies of the strip cavity can be obtained by solving the following standing-wave(resonant) conditions:Where L_eff is the effective cavity length(which should exceed the cavity' s real length owing to fields of SPs penetrating the metal and tunneling into grooves),ω_cavity is the resonant frequencies of the cavity, and k_cavity is the wave vector of the coupled SPs at the resonant frequencies and is determined by the lower-branch dispersion relation of the coupled SPs of MIM structure.When the cavity resonant frequencies are far from the groove absorption frequency,the tunneling frequencies of the low-frequency and high-frequency coupling modes are in agreement with the cavity resonant frequencies of L₁=L+62nm,L₂=L+110nm,L₃=L+162nm,L₄=L+158nm and L₅=L+203nm, respectively(Fig.2).Restated,the tunneling frequencies are primarily related to the cavity structure.As mentioned,different coupling modes have different effective cavity lengths,which results from the different SP fields which have different effects on waves penetrating the metal and tunneling into the grooves.When the resonant frequencies of the cavity are close to the absorption frequency of the groove,strong coupling exists between the groove and the cavity;hence,the tunneling frequencies deviate from the resonant frequencies of the cavity(thus,the effective cavity lengths change).In conclusion,we Investigate cavity-modulated resonant tunneling through a silver film with periodic grooves on both surfaces.A strip cavity embedded in the film affects tunneling frequencies via a coupling mode and waveguide mode.In the coupling mode,both the resonant tunneling through the gap between the groove and the cavity and the cavity itself form an entire resonant structure.