## 4 Simulation of Practical Spin Routing Device
In this way, we realized a dynamic tunable on-chip photonic routing device. Figure 9: The relationship between the SPP electric field intensity at point \(O\) and the incident wavelength. Considering that the wavelength will affect the spin sensitivity of the device, which may eventually lead to a failed identification of the input polarization state, we chose the center points of the two horizontal waveguides at the two sides of the aperture structure, i.e., the points (\(-\)17.5 \(\upmu\)m, 0.09 \(\upmu\)m) and (17.5 \(\upmu\)m, 0.09 \(\upmu\)m), to observe the spin sensitivity of this device in the wavelength range of 700 to 1200 nm. We used the SPP intensity contrast ratio of the two points as the evaluation criterion. Figure 10d shows the SPP intensity contrast ratio of the two points under LCP incident light in the wavelength range of 700 to 1200 nm, in which the red and black lines represent the SPP intensity at the points (\(-\)17.5 \(\upmu\)m, 0.09 \(\upmu\)m) and (17.5 \(\upmu\)m, 0.09 \(\upmu\)m) respectively, and the blue line represents the SPP intensity contrast ratio of the two points. It can be seen that the SPP intensity at the point (17.5 \(\upmu\)m, 0.09 \(\upmu\)m) is always very low, and the SPP intensity at the point (\(-\)17.5 \(\upmu\)m, 0.09 \(\upmu\)m) has a peak with a half height width of about 120 nm (950 to 1070 nm). In this wavelength range, the SPP intensity contrast ratio is larger than 8 dB. This means that the designed device has a wide working bandwidth. Similarly, we designed a three-channel routing device, which can be used for spin-controlled multicasting. The structure of the strip PMMA waveguides is illustrated in the inset of Figure 11a. Figure 11a shows the coupling of three nondiffracting SPP beams to the three PMMA waveguides when the inclined incidence angle is 0\({}^{\circ}\). In the simulation, the distance between the two subarrays on the different sides of the y-axis is \(\delta=1\)\(\upmu\)m, every column has 20 nano-rectangular slots, and the other parameters are the same as those used in Figures 9 and 10. It can be seen that the signal transmitted by the middle PMMA strip waveguide is the strongest because the intensity of the nondiffracting SPP beam of the main lobe is larger than that of the side lobes. All the three strip PMMA waveguides can receive nondiffracting SPP signals correctly and have high coupling efficiency. We also tested the working bandwidth of this multichannel photon router. Similar to Figure 10d, we used the SPP intensity contrast ratio of the center points of one waveguide and its symmetrical waveguide at the other side of the aperture structure as the evaluation criterion. The relationship between the intensity contrast ratios of the three pairs of waveguides and the incident wavelength are shown in Figure 11b-d, respectively. It can be seen that at the center point of the left-hand side middle waveguide, i.e., (\(-\)15.5 \(\upmu\)m, 0.09 \(\upmu\)m), the SPP intensity has a peak with a half height width of about 140 nm (935 to 1075 nm), within which the SPP intensity contrast ratio of the point (\(-\)15.5 \(\upmu\)m, 0.09 \(\upmu\)m) and its symmetrical  
Figure 10: **(a–c)** The coupling effect of a single nondiffracting SPP beam to different PMMA SPP waveguides when the inclined incidence angle is \(-\)7.5\({}^{\circ}\), 0\({}^{\circ}\), and 7.5\({}^{\circ}\), respectively. The inset in **(a)** is the structure scheme of the spin router. **(d)** The relationship between the incident wavelength and the SPP intensity at points (\(-\)17.5 \(\upmu\)m, 0.09 \(\upmu\)m) and (17.5 \(\upmu\)m, 0.09 \(\upmu\)m), in addition to their contrast ratio under LCP incident light. point (15.5 \(\upmu\)m, 0.09 \(\upmu\)m) is larger than 9 dB.