Single photonic crystal structure for realization of NAND and NOR logic functions by cascading basic gates

Abstract

In this article, we propose the realization of all-optical NAND and NOR logic functions on a single photonic crystal structure by cascading basic logic gates, viz. AND, OR, and NOT. Initially, to achieve this, a photonic crystal logic gate structure is designed with cross-shaped waveguide as a common gate for AND and OR functions, and another photonic crystal structure is devised with T-shaped waveguide as NOT gate. An additional input, namely reference input, is applied to these basic gate structures whose phase determines the type of the logic function in the former gate structure, and inevitable for NOT function in the latter one. The reference input is out of phase with the actual inputs in AND and NOT functions, whereas it is inphase in OR function. Simulation results show that the contrast ratio for AND, OR, and NOT is 11.74, 9.99, and 54.52 dB, respectively, with a response time of less than 0.15 ps. Later, these logic gate structures are cascaded to realize NAND and NOR functions, resulting a contrast ratio of 10.57 and 8.60 dB, respectively, at a response time of 0.152 ps. The percentage of reduction in the contrast ratio of the cascaded structure compared with the basic AND/OR gate is very small with a value of less than 1.5%. Moreover, the proposed NAND/NOR logic gate obtained by cascading the basic logic gates is quite compact with area occupancy lowered by a factor of 4.5 compared to the cascaded structures available in the literature.