# Two-Dimensional Permutation Vectors' (PV) Code for Optical Code Division Multiple Access Systems
## 5 Proposed 2D-PV W-T-Based OCDMA-PON
Each leg of the \(MUX_{w_{1}:1}\) contained a bandpass filter that was tuned to allow the required spectrum with  
Figure 7: Transmitter module. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|} \hline \multirow{2}{*}{\(A_{g,h}\)} & \(\mathbf{\lambda_{1}}\) & \(\mathbf{\lambda_{2}}\) & \(\mathbf{\lambda_{3}}\) & \(\mathbf{\lambda_{4}}\) &  
correspondence to the chip placement in \(X^{ht}\) code sequence, as shown in Table 3. Consequently, for user \(U_{0,0}\), the spectral encoder allowed the spectrum located at \(\lambda_{3}\) and \(\lambda_{7}\), respectively. Consequently, the 2D temporal and spectral encoding operation for the coder word \(A_{0,0}\) of user \(U_{0,0}\) was achieved at the transmitter module. Then, the end face of the spectral encoder was connected to a switching arrangement (SWA) via \(N_{K_{1}}N_{K_{2}}:1\) optical coupler \((OCU_{TX})\). The SWA was deployed to exploit the built-in redundancy of the ring topology and ensure desired connection availability at the feeder level. The SWA, as shown in Figure 6, contained a combination of \(1:2\ OCU_{SWA}\) and an optical switch, respectively, with port 1 as the input and ports 2 and 3 as the output ports, respectively. The \(1:2\ OCU_{SWA}\) received the encoded spectrum from \(N_{K_{1}}N_{K_{2}}:1\ OCU_{TX}\) via input port 1. The encoded spectrum was equally forwarded towards the output ports 2 and 3, respectively. Port 2 of the \(1:2\ OCU_{SWA}\) extended towards the optical distribution network (ODN) that further connected with multiple remote nodes, whereas port 3 was fed to an optical switch \(1:2\ SW_{SWA}\), as shown in Figure 6.  
Under normal working conditions, port 2 of the \(SW_{SWA}\) is connected to an optical null and all traffic propagates in a clockwise direction towards the ODN, as shown in Figure 6 using red fiber. However, in a case of failure or cuts in the feeder fiber, Optical line terminator (OLT) unit directs the \(SW_{SWA}\) to change its position from port 2 to port 3, which provides a clockwise and counterclockwise flow traffic until the point of failure. Consequently, the proposed architecture can provide extended connection availability along with high spectral efficiency in comparison with the existing architecture. ODN essentially contains a combination of ring-based feeder fiber \((FF_{R})\), remote nodes \(\left(RN_{K_{2}}\right)\), distribution fibers \((DF_{N})\), and optical network terminals (ONTs). One end of the \(FF_{R}\) relates to port 2 of the \(OCU_{SWA}\) in order to carry the traffic towards the ODN in a clockwise direction under a normal mode of operation, whereas, the other end terminated at port 3 of the \(SW_{SWA}\), as shown in Figure 6. \(FF_{R}\) also contains multiple \(RN_{K_{2}}\) to carry the traffic from feeder level to the respective ONTs at the distribution level. Each \(RN_{K_{2}}\) consisted of two OCUs with the split ratio of \(1:2\left(OCU1_{RN_{1}}\right)\) and \(1:K_{1}\left(OCU2_{RN_{1}}\right)\), respectively. For user \(U_{0,0}\), \(RN_{1}\) was considered, as shown in Figure 6. The \(OCU1_{RN_{1}}\) received the \(FF_{R}\) through its input port 1 and split the incoming signal into two equal portions. One portion (via port 2 of the \(OCU1_{RN_{1}}\)) of the incoming signal was sent towards the \(OCU2_{RN_{1}}\), whereas another portion (via port 3 of the \(OCU1_{RN_{1}}\)) was forwarded towards the \(RN_{2}\) (Figure 6). The spectral/temporal multiplexed signal was received from port 2 of the \(OCU1_{RN_{1}}\) via the input port of the \(OPCU2_{RN_{1}}\). The second optical coupler at \(RN_{N}\) had a split of \(1:K_{1}\), which was used to carry the encoded spectrum towards the concerned ONTs via their respective DFs. Port 3 of the \(OCU1_{RN_{1}}\) further extended the ring-based fiber and was connected to the \(RN_{2}\), which consisted of the similar arrangement as discussed earlier.