An all-optical XOR gate was designed to take advantage of the previously unused silicon dioxide (SiO 2) interconnect layers in a microelectronic chip. The device relies on the coupling of modes between parallel waveguides and the interaction of the modes with the metal interconnects of a silicon chip to obtain a phase difference between input arms. When the signals from the two input arms interfere, the result is a logic XOR operation due to the phase difference. The design was numerically implemented, and a contrast of 18.7 dB was obtained with a 13.2-μm-long logic gate.