# An Eight-Channel C-Band Demux Based on Multicore Photonic Crystal Fiber
## 3 Results  
The 1 \(\times\) 8 PCF wavelength demultiplexer structure was simulated using an RSoft Photonics CAD suite software, which is based on the BPM. Figure 2 shows the optimal geometrical parameters (d/\(\Lambda\)) of the 1 \(\times\) 8 wavelength demultiplexer multicore PCF structure for the operating wavelengths. It can be noticed from Figure 3 that the optimal value is 0.85 for the operating wavelengths, and the values of d and \(\Lambda\) are 0.97 \(\upmu\)m and 1.14 \(\upmu\)m.  
The coupling length size for each operating wavelength was calculated by simulating the transfer energy between two closer silica cores. Figure 3a,b show the full transfer energy between port 1 and port 8 at the Z-range from 0-600 \(\upmu\)m for the 1565-nm operated wavelength. From Figure 3b, it can be noticed that the coupling length value is 203.41 \(\upmu\)m. The same simulation was done for each of the operating wavelengths, and the values of the coupling length were found as shown in Table 2.  
Figure 3: Energy transfer between core 1 and core 8 for the 1565-nm wavelength. (**a**). Intensity profile. (**b**). Normalized coupling efficiency as a function of the propagation direction.  
Figure 2: Normalized coupling efficiency as a function of the geometrical parameters of the multicore photonic crystal fiber (PCF) (d/\(\Lambda\)) for the operating wavelengths.  
By using the results taken from Table 2 and combining them with Equation (2), the locations and the lengths of the silica rods that are suitable for the 1 \(\times\) 8 wavelength demultiplexer multicore PCF can be found, and their values are: L\({}_{\text{main}}\) = 2.03 cm, L\({}_{\text{right,1}}\) = 0.98 cm, L\({}_{\text{left,1}}\) = 0.96 cm, L\({}_{\text{right,2}}\) = 0.43 cm, L\({}_{\text{left,2}}\) = 0.525 cm, L\({}_{\text{right,3}}\) = 0.485 cm, and L\({}_{\text{left,3}}\) = 0.545 cm. Using these results along with the optimizations over the multicore PCF length, the locations (2.03-2.5 cm at the Z-axis in core 1, 3.01-3.445 cm at the Z-axis in core 4, and 3.46-4 cm at the Z-axis in core 5) of the three selected switch LiNbO\({}_{3}\) layers were found. In addition, the eight output port layers were optimized in order to obtain a compact 1 \(\times\) 8 demultiplexer, and their locations are found as shown in Figure 1a.  
Figure 4a shows the light propagation of the 1530-nm wavelength in the PCF structure, and its optical path can be described as follows: z = 0-1.9 cm, light coupled between port 1 and port 8; z = 1.9-2.5 cm, light confined in port 1; z = 2.5-2.6 cm, light coupled from port 1 to port 5; z = 2.6-3.5 cm, light coupled between port 5 and port 7; z = 3  
Figure 4: Intensity profile of the 1 \(\times\) 8 multimode interference (MMI) wavelength demultiplexer. (**a**) \(\lambda_{1}\) = 1530 nm (port 1). (**b**) \(\lambda_{2}\) = 1535 nm (port 2). (**c**) \(\lambda_{3}\) = 1540 nm (port 3). (**d**) \(\lambda_{4}\) = 1545 nm (port 4). (**e**) \(\lambda_{5}\) =1550 nm (port 5). (**f**) \(\lambda_{6}\) = 1555 nm (port 6). (**g**) \(\lambda_{7}\) = 1560 nm (port 7). and (**h**) \(\lambda_{8}\) = 1565 nm (port 8).  
BPM simulations combined with the Matlab script code were performed to determine the 1 \(\times\) 8 wavelength PCF demultiplexer properties. Figure 5 shows the optical bandwidth transmission results for wavelengths around the C-band range (1530-1565 nm).  
From Figure 5, combined with Equations (3) and (4), the values of the cross-talk, insertion losses and full width maximum (FWHM) can be found. Table 3 shows the values of the cross-talk, bandwidth (FWHM), and loss for each port.