  Considering the coherent nonlinear dynamics between two weakly linked optical
waveguide arrays, we find the first example of coexistence of Josephson
oscillations with a novel self-trapping regime. This macroscopic bistability is
explained by proving analytically the simultaneous existence of symmetric,
antisymmetric and asymmetric stationary solutions of the associated
Gross-Pitaevskii equation. The effect is, moreover, illustrated and confirmed
by numerical simulations. This property allows to conceive an optical switch
based on the variation of the refractive index of the linking central
waveguide.
