## 4 3D-VWZCC System Description  
The incoherent OCDMA transceiver system based on the suggested three-dimensional VWZCC code is presented in Figure 2; this system is composed of four essential blocks: data generation unit and optical source, 3D-VWZCC encoder, 3D-VWZCC decoder, and information retrieval unit. Moreover, the system contains K (\(K_{1}K_{2}K_{3}\)) combinations of transceivers and P star couplers, while each subscriber is assigned by the signature 3D-VWZCC code word \(A_{g,h,l}\); the system is described as follows: the transmitter part (Figure 2a) contains an information generator (image, video, sound, etc.), on/off keying modulator, electrical/optical modulator, incoherent optical source, M spectral components of fiber Bragg grating FBGs (\(FBG_{1}\) and \(FBG_{2}\)), N temporal components, and P spatial components.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & \(R^{(0)}\)**(g,h,l)** & \(R^{(1)}\)**(g,h,l)** & \(R^{(2)}\)**(g,h,l)** & \(R^{(3)}\)**(g,h,l)** \\ \hline \(g=0\cap h=0\cap l=0\) & \(W  
In the first phase, the data coming out of the information source are modulated by on/off keying, then combined with an incoherent optical source and converted into the optical domain using an external MZM modulator (Mach-Zehnder modulator); then, the optical pulses are transmitted to the fiber Bragg gratings (\(FBG_{1}\) et \(FBG_{2}\)). The first time, the optical pulses are encoded by the \(FBG_{1}\) according to the spectral sequence \(X_{g}\), where the encoder \(FBG_{1}\) encoder selects specific wavelengths and reflects them, whereas the others that are different from (1) are eliminated. The second time, the selected wavelengths are sent to the \(FBG_{2}\) spectral encoder to compensate for the run-trip delay. We note that \(FBG_{2}\) has the same number of gratings as \(FBG_{1}\) but with reversed arrangements.  
In the second phase, the wavelengths leaving the spectral encoder \(FBG_{2}\) are sent to the delay lines to apply the time spread according to the time sequence \(Y_{h}\), where the input of the delay lines is divided into \(W_{2}\) equal parts. Furthermore, once the time coding is complete, the optical signals are multiplexed and propagated to the demultiplexer for spatial coding.  
In the third phase, the pulses in the output of the demultiplexer are divided into identical versions equal to \(W_{3}\) and are connected to the star couplers to perform the spatial coding according to the sequence \(Z_{l}\). In this case, the optical signal is coded in the 3D-VWZCC code.  
The design of the 3D-VWZCC receiver is shown in Figure 2b, and contains several components: optical signal multiplexer (combiner), correlator, two sets of fiber Bragg gratings FBGs (\(FBG_{1}\) and \(FBG_{2}\)), photodiodes PDs, and low pass filters (LPFs). The process of receiver that is the reverse of transmitter is described as follows: the optical signals received by the couplers are combined by the multiplexer according to \(Z_{l}\). and shared to \(W_{2}\) equal signals by the correlator and connected with the delay lines for the time decoding according to \(Y_{h}\), then the pulses at the output of the time delay lines are connected with fiber Bragg gratings FBGs for spectral decoding, where in the first step, the pulses are passed to \(FBG_{1}\) to select specific wavelengths according to the sequence \(X_{g}\), and filtered the others. Then, the selected pulses are reflected and sent to \(FBG_{2}\) to compensate for the delays introduced due to the \(FBG_{1}\) encoding. As a result, three-dimensional decoding has been performed. After that, the resulting optical signal is passed through to the photo-detector PD to convert the optical signal to an electrical signal in a direct way due to the ZCC  
Figure 2: 3D-VWZCC OCDMA transceiver system. (**a**) Transmitter; (**b**) Receiver.  
property, and finally, the low pass Bessel filter (LPF) is used to extract the desired data according to the data sent by the transmitter.