Ultra-compact all-optical logical circuits for photonic integrated circuits

Abstract

Abstract In this paper, a photonic crystal based ultra-compact Optical XOR gate followed by an optical half-subtractor is proposed. Plane wave expansion is used to evaluate the photonic bandgap of the devised structure. The output and efficiency of logical circuits can be improved by maintaining distinct thresholds for the output logic states, thereby enabling the design to operate even in low power inputs. Reliability of the structure is enhanced by retaining a threshold for the output value. The performance of the proposed circuit is examined using the Finite Difference Time Domain method. The output is considered as logic 1 when the power level exceeds 0.7 μW and logic ‘0’ if it is below 0.35 μW. The proposed logical circuit has high contrast ratio. The XOR gate has a contrast ratio of about 12.55 dB, and the half subtractor has 7.78 dB and 11.76 dB for Difference and Borrow respectively. These devices work at 1550 nm wavelength and are ultra-compact in size. The proposed structure of logic gates will be suitable for photonic integrated circuits due to its ultra-small and simple design.