Ultracompact all-optical full adders using an interference effect based on 2D photonic crystal nanoring resonators

Given the special place of hybrid logic circuits such as all-optical full adders in next-generation digital systems, a new kind of these structures using two-dimensional (2D) photonic crystals (2D-PC) is designed and simulated herein. The proposed structure is made of a hexagonal nanoring resonator (NRR), a coupling rod, and several waveguides. In this all-optical full adder, the mechanism of the interference effect in the PCs is used to simplify and minimize the structure. To make the structure flexible, the radius of the dielectric rod in the whole structure and the NRR are considered based on a lattice constant of 0.2a and 0.04a, respectively. The structure is operated at a wavelength of 1550 nm, considering the value of the power entering the waveguides and that exiting the Carry and Sum ports. To analyze the all-optical full adder, the plane-wave expansion method and finite-difference time-domain method are applied respectively to calculate the bandgap diagram and obtain the transmission and propagation of the optical field. In the proposed structure, the contrast ratio at the Carry and is been investigated in a unique and novel way, yielding values of 10.68 and 9.03 dB, respectively. In addition, the maximum and minimum response time for the Carry and Sum are obtained as 1.6 and 0.75 ps, respectively. The total footprint of the structure is about 183 µm². Due to its ultracompact size, low power consumption, fast response time, and simple structure, this all-optical full adder is suitable for use in low-power optical integrated circuits.