Decorrelation Bandwidth of Intercore Crosstalk in Weakly Coupled Multicore Fibers With Multiple Interfering Cores

The decorrelation bandwidth of the intercore crosstalk (ICXT) power generated in a weakly coupled multicore fiber (MCF) with multiple interfering cores is studied. For the first time, this is accomplished using a closed-form expression of the equivalent autocovariance function of the ICXT power that enables evaluating the correlation between the ICXT power generated at two different frequencies using a theoretical model to describe the stochastic evolution of the ICXT over time. It provides fast and reliable estimates of the decorrelation bandwidth of the ICXT induced by multiple interfering cores with arbitrary relative time delays (skews) between cores, which represents a crucial tool to assist the design of new MCF systems. Validation of the autocovariance and decorrelation bandwidth expressions by numerical simulation and with experimental results published by other authors is accomplished. In contrast to the single interfering case, the equivalent autocovariance of the ICXT induced by multiple interferers may present several inflexion points along the frequency lag due to the different core contributions that may be characterized by different skews. For MCFs with similar skews between cores, the equivalent autocovariance has, approximately, a sinc-squared shape with the decorrelation bandwidth, defined as the first zero of equivalent autocovariance, occurring at the frequency lag, in Hz, given by the inverse of the skew. When the decorrelation bandwidth of the ICXT induced by multiple interfering cores is much lower or much higher than the signal bandwidth, the ICXT mechanism can be considered as uncorrelated noise or as a static coupling component, respectively. When the decorrelation bandwidth is similar to the signal bandwidth, the ICXT mechanism should be treated as correlated noise.