All-optical ultrafast logic gates that use asymmetric nonlinear directional couplers.

All-optical ultrafast AND, OR, and XOR logic functions that use asymmetric nonlinear directional couplers are numerically demonstrated. In such an asymmetric coupler, different Kerr effects are generated when the same power is launched into two waveguides. The output power tends to appear in the waveguide of stronger Kerr effect when only one waveguide is excited. When both waveguides are excited, the output power contrast between the two waveguides depends on the relative phase of the two input signals. The parameters of fiber couplers are used to demonstrate the logic functions.