We study for the first time the evolution of the guided field in a 1×7 fibre coupler with a third-order nonlinearity. An analytical solution of the nonlinear coupled-mode equations is presented in terms of the Weierstrass function. In particular, we found that contrary to the equal power distribution in the linear limit, a cross-state appeared if the coupler was initially excited in the central core and a certain input power was chosen. Finally, we analyse the far-field pattern of the coupler output
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