# Suppressed Transmission of Long-Range Surface Plasmon Polariton by TE-Induced Edge Plasmon
## 3 TE-Induced Edge Plasmon  
We investigated the plasmonic response of G-SPPWs using FDTD analysis in the presence of incident polarized light across the 4 \(\upmu\)m gap, as considered in the previous study [38]. When TE-polarized light is excited in the channel waveguide, its electric field oscillates parallel to the planar plane of the PSC (\(x\)-\(y\) plane) and accumulates electric charges at the end(front)-facet of input(output) SPPWs. As a result, the light excites a plasmonic mode in the gap. Figure 2a shows the FDTD-calculated cross-sectional mode profile of the excited mode in the gap due to the TE-polarized light. The inset shows the zoomed mode profile in the right edge (output SPPW). The edges of G-SPPWs are surrounded by the core of the channel waveguide (n\({}_{\text{core}}\) = 1.46). Most of the fields are highly localized at the edges and the effective index is 1.48737, which indicates that the dispersion curve of the excited mode lies to the right of the respective light line, and an edge-guided plasmonic mode is excited in the gap by the TE-polarized light. Figure 2b shows the induced current density by the edge plasmon at the top and bottom interfaces of G-SPPWs. It is observed that the excited edge plasmon is a short-range SPP (SRSPP) [46], as the surface charge oscillates symmetrically at the top and bottom interfaces. The SRSPP exhibits apparently distinct characteristics from LRSPPs in field confinement and attenuation, inducing a strong current density. The induced current densities (J\({}_{x}\) and J\({}_{y}\)) are normalized to the amplitude of J\({}_{x}\) by LRSPPs (J\({}_{\text{LRSPP}}\)), to characterize the impact on the LRSPP propagation by the TE-inducededge plasmon. Far stronger current densities than that of the LRSPP are induced near the edges, and the symmetry of current density carried by the LRSPP would break if the LRSPP and TE-polarized light were incident to the gap coincidently. Therefore, the LRSPP propagating along the input SPPW radiates by scattering before it reaches the structural interruption (end-facet of the input SPPW). We defined the decoupling length (Ld) as the summation of the gap length and the lengths for which the TE-induced current density is larger than that which is carried by the LRSPPs at the G-SPPWs. Ld represents the extended radiation length by TE-induced edge plasmon. The decoupled LRSPP by the edge plasmon radiates freely for the decoupling length and re-excites LRSPPs at the output SPPW, which leads to the suppressed transmission of LRSPPs by the extended radiation length. On the other hand, TM-polarized light exhibits quite a different response in the gap. The magnetic field of TM-polarized light excited in the channel waveguide oscillates parallel to the planar plane of PSC, and the electric field mainly oscillates in the \(z\)-axis. Figure 3a shows the cross-sectional mode profile of the excited mode in the gap by TM-polarized light, and the white solid line represents the 6 \(\times\) 6 \(\mu\)m\({}^{2}\) core of the channel waveguide. Most of the field is distributed in the core with a refractive index of 1.46. The mode profile is almost the same; the fundamental TM mode is excited in the channel waveguide and the effective index is 1.45607, which indicates that a photonic TM mode guided by the core is excited in the gap. Figure 3b shows the induced current density by the photonic mode at the top and bottom interfaces of G-SPPWs. Compared to the TE-induced current density, minute amounts of current density are induced, and the normalized value is also under 1, which implies that TM-induced current density cannot disturb the propagation of LRSPPs; therefore, all the power contained in incidental TM-polarized light passes across the gap in the photonic state without any disturbance to the LRSPP. The suppressed transmission of LRSPPs by TE-induced edge plasmon was investigated experimentally for a wide range of the input optical power in PSC (0-21 dBm). The TE-polarized optical signals were modulated at 3 Hz frequency by the attenuator.