  We demonstrate that the interaction of loop and nonlinear Fano resonances
results in a formation of hybrid resonant states in Mach-Zehnder type
interferometers, providing with opportunities for an advanced phase
manipulation. The nonlinear response of such structures can be greatly
enhanced, leading to a low threshold 100% switching operation. We further
propose one of the possible realizations based on nonlinear photonic crystal
circuits, suitable for optimal all-optical switching.
