An electro-optic comparator based on photonic crystal ring resonators covered by graphene nanoshells

A logic comparator is a digital circuit comprised of numerous transistors on an integrated circuit that compares two binary numbers. Researchers have proposed various designs for implementing comparators using logic gates, but most are based on DC electrical signals, which suffer from slow switching speeds and high power consumption. This paper presents a novel design for a fast and tunable electro-optic single-bit comparator utilizing graphene-coated nanoshells (GNSs) in photonic crystal (PhC) ring resonators. The comparator's structure includes three inputs, three GNS-coated ring resonators, several waveguides for comparison, and three outputs created in a PhC microstructure in an area of 760 µm². A continuous-wave laser source centered at 1550 nm is applied to the first input to enable the proposed photonic chip. Two other inputs are utilized to apply electrical voltages, and the comparator's task is to compare them. The optical signal applied to the enable input port is directed to the corresponding output depending on the comparison result. We used the finite-difference time-domain method to study the light propagation inside the proposed structure to solve Maxwell's equations. Numerical simulations demonstrate that the designed structure has a very short delay time of 1.85 ps, faster than previously reported comparators, including electronic, optoelectronic, and all-optical comparators. The proposed comparator's rapid response, small area, and tunability make it an appropriate device for optical applications in photonic integrated circuits.