Directed XOR/XNOR logic circuit implemented by microring resonators: simulation and demonstration

A directed logic circuit consisting of two silicon microring resonators which can perform XOR and XNOR operations has been proposed. These two operations are evaluated as the optical signal is directed along the circuit, and the results appear at some specific output ports of the circuit. A potential advantage of this new logical paradigm is that it has markedly less state delay than traditional logic circuits. Devices based on the above proposal are fabricated on an 8-inch silicon-on-insulator wafer. The microring resonators in the circuit are modulated through thermo-optic effect. Two electrical modulating signals applied to the microring resonators represent the two operands of the logical operation respectively. Bitwise XOR and XNOR operations at 20 kbit/s are demonstrated. The scattering matrix method is adopted to analyse the transmission spectra of the circuit. The symmetrical characteristics of the spectra are well described by this model. The potential applications of this device are given.