Design and Simulation of an Ultra-Fast All-Optical Single-Bit Comparator Based on Photonic Crystal Ring Resonators

A digital comparator is a logic circuit used to compare two binary numbers. So far, various designs have been proposed using logic gates, which are mainly based on electrical signals and lack the desired high speed. This paper presents a new design of an ultra-fast all-optical single-bit comparator based on photonic crystal ring resonators consisting of highly nonlinear glass. The structure of this comparator consists of two inputs, four ring resonators with a number of waveguides for comparison and three outputs for displaying the result, all created in a photon crystal bed. Using the plane wave expansion method, its band structure is calculated and the results show that the fundamental photonic crystal has a photonic band gap in the polarized TM mode in S, C and L bands that is a suitable tool for telecommunication applications. To solve the Maxwell's equations, the  finite-difference time-domain method is used, which aims to investigate the light propagation inside the final structure. The results of numerical studies show that the designed structure has a very short response time of 3 ps, making it faster than all the comparators designed so far, including electronic, electro-optical and all-optical comparators. Also, its relatively small area of 826 μm2 makes it applicable in the design of photonic integrated circuits.