## 4 Node Architecture of Extended SAC Label Generation and Recognition  
The edge node architecture for generating extended SAC labels in GMPLS networks is shown in Figure 4. Edge nodes transfer the path information of packets into a label stack. A broadband light source (BLS) is coupled to \(M\) optical band-pass filters (OBPFs) to construct \(M\) WDM channels. Each OBPF has an equal bandwidth but different central frequencies. Encoder group \(j\) encodes MLS codes **C**(1), **C**(2),..., **C**(\(N\)) on the \(j\)-th WDM channel to generate labels **E**(1, _j_), **E**(2, _j_),..., **E**(\(N\), _j_). An optical cross-connect (OXC) establishes the connections for the labels required for packet switching. Finally, an optical coupler aggregates the labels to form a stack. A Mach-Zehnder modulator (MZM) modulates the payload bit stream on the intensity of stacked labels. Figure 4: Edge node architecture for generating extended SAC labels. Figure 3: Time waveform and power spectral density (PSD) of an optical packet traveling along (**a**) LSP 1; (**b**) LSP 2. The label generation scheme of the proposed extended labels (\(N=3\), \(M=3\)) is shown in Figure 5. We use MLS codes of (\(N=3\), \(\omega=2\), \(\lambda=1\)) as the label basis. Three MLS codes are defined as **C**(1) = (1,1,0), **C**(2) = (0,1,1), and **C**(3) = (1,0,1), respectively. Note that **C**(\(i+1\)) is the cyclic-shift vector of **C**(\(i\)) for one chip. The wavelength signals in channel \(j\) enter the first and second input ports of AWG \(j\) for encoding. The selection of AWG ports (port 1 and port 2) corresponds to the positions of chip \"1s\" in MLS code (1,1,0). For **E**(1,1) = (1,1,0,0,0,0,0,0,0), it is generated at the first output port of AWG 1 and represented by a wavelength distribution of {\(\lambda_{1}\),\(\lambda_{2}\),0,0,0,0,0,0,0}. Based on the wavelength-routed property of AWG, **E**(2,1) and **E**(3,1) are shown at the second and third output ports of AWG 1, which are represented as {0,\(\lambda_{2}\),\(\lambda_{3}\),0,0,0,0,0,0} and {\(\lambda_{1}\),0,\(\lambda_{3}\),0,0,0,0,0,0}, respectively. We take the example of label distribution of LSP1 in Figure 2, where the connections in LSP1 match labels of **E**(1,1), **E**(2,1), and **E**(3,2). Therefore, an OXC switches these three signals to a coupler for label stacking. The wavelength components in the stack signals are the summation of the three individual labels. The architecture of the core node with extended SAC label recognition is shown in Figure 6. Core nodes switch and forward packets based on the decoded signals of stacked labels. For simplicity, we demonstrate a node structure with a single input port and \(k\) output ports. An optical splitter separates the received packet into two signals with an identical waveform but only half of the power. One of the signals is split into \(j\) streams and sent to \(j\) OBPFs for label decoding, while the other is queued in a fiber delay line (FDL). After label recognition is performed, the decoded signals \(d(i,j)\) of extended labels \(\textbf{E}(i,j)\) control an OXC to switch the packet to the correct path. Note that the setups of OBPFs and decoder groups are varied based on the path connections to the core node. Figure 7 shows the process of label recognition based on an AWG decoder. In this example, we demonstrate the packet switching process along LSP 1 at core node 4 in Figure 2. The decoder structure includes a pair of AWGs and two balanced detectors connected to the AWG outputs. The decoded signal \(d(i,j)\) used for identifying **E**(\(i,j\)) can be derived by performing correlation subtraction expressed as follows. \[\textbf{E}(i,\ j)\odot\textbf{E}(k,\ l)-\overline{\textbf{E}}(i,j)\odot \textbf{E}(k,l)\ =\ \left\{ \begin{array}{ll}\frac{N+1}{2},\ i=k,j=l.\\ 0,\ \ \ \ \ i\
eq k,j\
eq l.\end{array} \right. \tag{4}\]  
where \(\overline{\textbf{E}}(i,j)\) is the complementary code of \(\textbf{E}(i,j)\). As **E**(2,1) is included in the label stack, the decoded signal \(d\)(2,1) has a relatively high amplitude.