# Numerical Study of a Polarization Selective Visual Optical Switch
## 3 Results and Discussions
### The Influence of the Changing of Metal Strip Material on the Enhanced Optical Transmission  
Considering the replaceable of the metal strip, the material types of the strip are changed, including nickel (Ni) and silicon (Si). It is known from the literature that as a broadband absorption layer, ultra-thin nickel film can obtain rich structural colors with high saturation and brightness in the visible light band [29]. Silicon, as a semiconductor material, has high carrier mobility and can promote the excitation of surface plasmons [30]. Note that the geometric parameters of the structure are consistent with that of the Al material, only the material of the metal strip is changed. As shown in Figure 5a-c, the number of Ni metal strips are 1, 2, and 3, respectively. It can be seen from the figure that when the polarization direction of incident light are 0\({}^{\circ}\)and 90\({}^{\circ}\), the colors of the material are different from that of the Al. In addition, through the calculation of Equation (7), it is found that the contrast ratio of the optical switch is relatively small. It is worth noting that when the strip material is Si in Figure 5d-f, the brightness of the color presented by the material is relatively high. It is generally known that the carrier concentration of silicon material is higher than that of the Al and Ni, resulting in higher transmittance.  
In order to study its physical mechanism radically, the distributions of relative electric field intensity in X-Y plane when the strips material are Ni and Si are given. As shown in Figure 6a-f, the distributions of relative electric field intensity when the polarization direction of incident light are 0\({}^{\circ}\). Obviously, the charges are basically distributed at the sharp corner of the material strip. In Figure 6(a1-f1), a large amount of electric charge are also accumulated between the material strips. There is not difference between this material strips and Al material. To date, the number of material  
Figure 4: Transmittance diagram in different situations. (**a1**) When there is no metal strip in the hollow hole, the radius \(R\) of the hollow hole is changed; (**a2**) when there is no metal strip in the hollow hole, angle between incident light and normal direction of material surface; (**b1**) when the number of the metal strips is three, the \(L\) changes; (**b2**) when the number of the metal strips is three, the \(W\) changes.  
strips, material and geometric parameters have been studied. In order to understand more intuitively the influence of these conditions on the representation of color and the size of contrast ratio, all color modules (in Figure 7a-c), as well as CIE1931 color space inversion map distribution (in Figure 7d) are given. At the same time, in Tables 1 and 2, the contrast ratio and the working wavelength under each parameter are given.  
Figure 5: (**a–c**) Transmittances of different number of Ni metal strips; (**d–f**) Transmittances of different number of Si strips.  
Figure 6: The relative electric field distribution diagrams in the cases of different materials and the number of material strips. (**a–c**) is Ni; (**d–f**) is Si. When there is subscript, the polarization direction is 90\({}^{\circ}\).