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We propose a novel nonlinear switch-based on the irregularity in a three-core-doped photonic crystal fiber (PCF). We numerically investigate the proposed structure, which consists of air holes arranged in a triangular lattice around two defects separated by a single Er-Yb doped core. Its switching operation is based on the gain change in the doped core due to the nonuniformity and irregular structure around it. It is shown that by adjusting the gain in the doped core, the light is entirely transferred from the central core to the upper and lower ones. We have employed the full vectorial finite-element method and the finite-difference time domain to investigate and optimize the optical modes, nonlinear parameter, and gain effects on the switching operation. It is found that an optimum gain is essential to allow either a periodic exchange of the light between the upper and lower cores or independent core propagation. Possible nonuniformity in the hole diameters and irregularity problems of the proposed PCF design during the fabrication process have been predicted. The waveguide dispersion with respect to the doped central core region has been thoroughly investigated.