# An Eight-Channel C-Band Demux Based on Multicore Photonic Crystal Fiber
## 4 Conclusions  
This study shows how it is possible to implement the classical 1 \(\times\) 8 demultiplexer that is usually based on seven 1 \(\times\) 2 demultiplexer units in a cascade tree structure, only with one multicore PCF. In addition, this work shows how to control the light propagation direction inside the multicore PCF using the MTIR and bandage mechanism that enables light to be coupled only in the silica areas, and a strong light confinement in the LiNbO\({}_{3}\) and Si\({}_{3}\)N\({}_{4}\) areas.  
By analysis of the numerical results, it is clear that the main benefit is that the multicore PCF was designed without using additional device elements, which are usually required in order for the device to function as a 1 \(\times\) 8 demultiplexer. This benefit can lead to a new design of a compact DWDM system that can be utilized to obtain better performances. However, integrating this type of demultiplexer to the DWDM system will require modifying the mode field diameter (MFD) coming out from the multicore PCF. This is due to the DWDM system usually using silica fibers that have a large MFD compared to the multicore PCF. This issue can be solved by integrated a tapered fiber that can convert the MFD of the 1 \(\times\) 8 wavelength demultiplexer to the MFD of the DWDM system.  
Figure 5: Normalized power as function of the optical signals.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(\mathbf{\lambda_{n}}\) (nm) & **1530** & **1535** & **1540** & **1545** & **1550** & **1555** & **1560** & **1565** \\ \hline Port number & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\ Cross-talk (dB) & \(-\)16.65 & \(-\)16.73 & \(-\)16.88 & \(-\)16.81 & \(-\)16.6 & \(-\)16.32 & \(-\)16.08 & \(-\)15.93 \\ FWHM (nm) & 4.23 & 4.38 & 4.67 & 4.69 & 4.03 & 4.1 & 4.62 & 4.15 \\ Losses (dB) & 0.31 & 0.26 & 0.2 & 0.18 & 0.55 & 0.31 & 0.45 & 0.69 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Values of the cross-talk, full width maximum (FWHM), and losses for the operating wavelengths.  
The 1 \(\times\) 8 wavelength demultiplexer multicore PCF can be fabricated using a fiber fabrication facility with hybrid materials. The fabrication process cannot be carried out only by a staking or drawing technique; it also requires a microelectronic technique, such as the lithography technique, that can be used to integrate the LiNbO\({}_{3}\) and Si\({}_{3}\)N\({}_{4}\) layers over the multicore PCF length.  
To conclude, in this work, we have shown that a 1 \(\times\) 8 wavelength demultiplexer can be implemented using a multicore PCF structure with integrated LiNbO\({}_{3}\) and Si\({}_{3}\)N\({}_{4}\) materials.  
The simulation results showed that the operated wavelengths of 1530 nm, 1535 nm, 1540 nm, 1545 nm, 1550 nm, 1555 nm, 1560 nm, and 1565 mm, with a short spacing of 5 nm and supporting the whole C-band range, can be separated after a propagation length of 5 cm with a bandwidth range of 4.02-4.69 nm.  
The proposed device has low cross-talk ((-16.88)-(-15.93) dB) with an insertion loss of 0.18-0.69 dB.  
Thus, this device has the potential to increase the data bitrate in an optical communications system that works on DWDM technology.  
This research can be used in future work to design a powerful and new demultiplexer device based on multicore polymer/silica fiber in a very similar way, and with the right materials' modification.  
Although only the 1 \(\times\) 8 wavelength demultiplexer configuration is considered in this paper, the demultiplexer can also operate as a multiplexer with a reversed direction of the guided light.  
[PERSON] envisioned the project. [PERSON] designed the device and performed simulations with support of [PERSON]. [PERSON] wrote the manuscript and the reply letter. [PERSON] made all figures and all authors reviewed the manuscript. This research received no external funding. The authors declare no conflict of interest.