Multi-functional all-optical photonic crystal logic gate using nonlinear directional coupler

In this paper, an all-optical photonic crystal multi-functional logic block is proposed based on the nonlinear directional couplers. This structure provides XOR/Majority and XNOR/Minority logic functions on a single structure and also, offers a full adder and its inverted logic circuits. Four different logic operations of the proposed structure can be determined in the output port using two selection signals. The nonlinear rods in the proposed device are made of the silicon nanocrystal to provide the required phase shift for different input powers. The finite difference time-domain and the plane wave expansion methods are used to simulate and analyze the proposed logic block operation. The effect of variations in the radius and the position of rods on the performance of the proposed logic block, has been investigated, which indicate that the proposed logic block has little sensitivity to the process variation problem. The maximum required switching power and the propagation delay of the proposed logic block are 5 W and 1.2 ps, respectively.