We investigate the formation of dark vector localized structures in the presence of nonlinear polarization mode coupling in optical resonators subject to a coherent optical injection in the normal dispersion regime. This simple device is described by coupled Lugiato-Lefever equations. The stabilization of localized structures is attributed to a front locking mechanism. We show that in a multistable homogeneous steady-state regime, two branches of dark localized structures can coexist for a fixed value of the system parameters. These coexisting solutions possess different polarization states and different power peaks in the microresonator. We characterize in-depth their formation by drawing their bifurcation diagrams in regimes close to modulational instability and far from it. It is shown that both branches of localized structures exhibit a heteroclinic collapse snaking type of behavior. The coexistence of two vectorial branches of dark localized states is not possible without taking into account polarization degrees of freedom.
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