## 3 Numerical Results
### OP Dependence on the Number of Interfering Cores  
All preceding results regarding the OP have considered only one interfering core with PAM4 format. However, several cores may contribute to the ICXT [2; 9; 14; 16; 48]. In a weakly-coupled MCF, the number of interfering cores with a significant contribution to ICXT on one specific interfered core typically does not exceed 8 [48], which corresponds to the number of closer neighboring cores (with shorter core pitch) to the CUT [48]. In the following, the OP is assessed for 1, 2, and 4 interfering cores, for \(L=80\) km, where signal-ASE beat noise is dominant over electrical noise, for \(r=0\) and \(r=0.1\), \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\). All simulated OP with \(N_{i}=4\) were achieved in about three weeks of simulation, in a computer with a 16 GB RAM with and four 3.2 GHz processors. The simulation with eight interfering cores was not performed due to the high required simulation time of about six weeks. Figure 4 shows results of the OP as a function of the ICXT level, for \(N_{i}=1\), \(N_{i}=2\) and \(N_{i}=4\), for (a) \(|S_{mn}\cdot R_{s}|=0.01\) and (b) \(|S_{mn}\cdot R_{s}|=1000\), and \(r=0\) and \(r=0.1\). All interfering  
Figure 3: Maximum acceptable ICXT level required to achieve the OP \(=10^{-3}\) and OP \(=10^{-4}\) as a function of the MCF length, for \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\), for \(r=0.1\). Figure 2: OP as a function of the ICXT level, for \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\), for \(r=0.1\) and one interfering core. The dashed lines represent a cubic interpolation of log\({}_{10}\)(OP). cores have the same SSRP. It is possible to observe that, for both SSRPs, increasing the number of interfering cores from 1 to 2 and 4 results in an increase of the OP for all presented ICXT levels, regardless of the extinction ratio, due to the higher number of interfering cores contributing to ICXT. For OP = \(10^{-4}\), Figure 4 shows an enhanced tolerance to ICXT exceeding 6 dB, for systems with \(|S_{mn}\cdot R_{s}|\) = 1000, when comparing \(r=0.1\) with \(r=0\), for all the different numbers of interfering cores. For \(|S_{mn}\cdot R_{s}|\) = 0.01, the ICXT tolerance is not so significantly affected by the extinction ratio variation, with the tolerance to ICXT not exceeding 1.3 dB. Furthermore, Figure 4 indicates that the OP degradation with the increasing number of cores is similar, for \(|S_{mn}\cdot R_{s}|\) = 0.01 and \(|S_{mn}\cdot R_{s}|\) = 1000. The maximum acceptable ICXT levels for OP = \(10^{-4}\), for each SSRP and extinction ratio pair, extracted from Figure 4, for \(N_{i}\) = 1, \(N_{i}\) = 2 and \(N_{i}\) = 4, are presented in Table 2. In Table 2, it is possible to observe that, for OP = \(10^{-4}\), doubling the number of cores, i.e., from 1 to 2 and from 2 to 4, for \(r=0\) and \(r=0.1\), a maximum acceptable ICXT level reduction between 2.9 dB and 3.5 dB is observed. This reduction is not very dependent on the extinction ratio or on the SSRP regime. For an unamplified intra-datacenter link with 2 km with PAM4 format in the interfered core and OOK format in the interfering cores [25], for \(|S_{mn}\cdot R_{s}|\) = 1000 and \(r=0\), the maximum acceptable ICXT levels reduce around 3.8 dB,  
Figure 4: OP as a function of the ICXT level per interfering core, for 1, 2, and 4 interfering cores with PAM4 format, for (**a**) \(|S_{mn}\cdot R_{s}|\) = 0.01 and (**b**) \(|S_{mn}\cdot R_{s}|\) = 1000, for \(r=0\) and \(r=0.1\). The dashed lines represent a cubic interpolation of \(\log_{10}\)(OP). from 1 to 2 and from 2 to 4 interfering cores, in order to achieve the same OP, which is not much different from our results. The OP was also studied for OOK transmission in weakly coupled MCFs with a SSRP comparable to \(|S_{mn}\cdot R_{s}|=0.01\)[19; 20]. In [19], a maximum acceptable ICXT level of around \(-16\) dB is required to achieve an OP \(=10^{-4}\), with one interfering core and \(r=0.1\).