Design and Simulation of an All-optical Half Adder Using Nonlinear Photonic Crystal Ring Resonators

All-optical adders play a key role in the next generation of all-optical digital circuits. In this paper, using nonlinear resonance rings based on 2D photon crystals, a new structure has been designed to implement an all-optical half adder. To implement the required nonlinear ring resonators, some nonlinear defects made of doped glass were introduced between the core and outer layer of the resonant rings. The refractive index of nonlinear materials with high Kerr coefficients is very sensitive to the variation of optical intensity, so one can design optical switches by combining these materials with resonant rings. Two nonlinear resonant rings are used for designing the proposed all-optical half adder. Both rings are designed such that they can drop optical waves when the optical intensity is less than the switching threshold, but when the optical intensity is more than the switching threshold, they cannot drop the optical waves. The final structure has two input and two output ports. The proposed structure was simulated using Rsoft photonics CAD. According to the simulation results when both inputs ports are OFF, both output ports will remain OFF. If only one of the input ports is ON, the S port will be ON, and C will be OFF. Finally, when both input ports are ON, the C port will be ON, and S will be OFF. Therefore, these results prove that the proposed structure can work as an all-optical half adder. The maximum rise time for the proposed structure is about 1.5 ps.