# Plasmonics Induced Multifunction Optical Device via Hoof-Shaped Subwavelength Structure
## 3 Results and Discussions  
By considering the incident light polarization sensitive of structure [23; 24], we altered the incident light polarization angles \(\theta\), that is, rotated from parallel to Y axes to perpendicular to Y axes. Figure 2 shows the electric field distribution and transmittance when the \(\theta\) changes. The surface plasmon resonance was excited in the U-shaped structure when \(\theta\) is 0, which is distributed in two tips of the U-shaped structure in Figure 2a; With the increase of the polarization angle \(\theta\), the charge in the tip gradually moved towards the middle. The charges converged completely in the middle of the U-shaped structure, when \(\theta\) is 90. The difference was that, the localized surface plasmon resonance was not excited in the rectangle structure when the \(\theta\) is 90, but with the increase of the angle, a large number of charges accumulate in the rectangle structure, resulting in the increase of the resonance intensity. To date, we find that with the increase of the angle \(\theta\), the transmission peak in the near-infrared range splits. Moreover, a new transmission peak is generated in the mid-infrared range in Figure 2b. In order to demonstrate the mechanism of this phenomenon, we compared the EOT phenomena of three structures. As shown as in Figure 3a: In the U-shaped structure, with the increase of the angle \(\theta\), peak I decreased and peak III increases in the near-infrared range; In the rectangle structure, peak II increases with the increase of the angle \(\theta\); The important is that, all the transmission peaks have not appeared to shift. That is to say, in the separate U-shaped structure and rectangle structure, the change of angle does not cause the shift of transmission peak. Combined with the electric field distribution diagram in Figure 2a, we can see that: with the increase of \(\theta\), the charge distributed in the tip of U-shaped structure gradually converges in the middle, causing the peak I decrease and the peak III increase. Therefore, the charge accumulated at the tip leads to the generation of transmission peak I, and the charge converges in the middle, which leads to the formation of peak III. Likewise, a large number of charges are excited in the rectangle, leading to the electric field increase, thus forming the peak II. But, in the hoof-shaped structure, as the electric field increases with the increase of electric charge in the rectangle, the U part is coupled with the resonance mode (LSP resonance) in the rectangle part, and then the Peak II and III shifts. However, it should be noted that the Peak I does not disappear completely when the angle is 90 degrees. Figure 2: **(a)** Spatial distributions of the electric near field \(E\) with the different incident polarization angles \(\theta\) on the plane of \(Z=375\) nm (detection plane), respectively. **(b)** Transmittance spectrum of hoof-shaped structure arrays with different \(\theta\) with \(P_{x}=P_{y}=600\) nm. As shown in Figure 3b, in the case of 0 degree, since the rectangle structure does not excite the LSP resonance, the electric field distribution of U-shaped structure is almost the same as that of hoof-shaped structure. This shows that the transmittance of U-shaped structure and hoof-shaped structure are basically the same in different wavelengths at 0 degree. When the angle is 90 degrees, we can see that the relative electric field intensity in the U part of the hoof-shaped structure is greater than that in the U-shaped structure alone. In other words, due to the addition of the rectangle structure, the effective refractive index n\({}_{\text{eff}}\) in the U part increases [25; 26], thus causing the redshift of the Peak III. It cannot be ignored that the excitation of the LSP resonance mode in the rectangle also makes the charge in the tip of the U part slightly increase, which is also the reason why the Peak I does not disappear completely.