All-optical XOR and OR by Mach-Zehnder Interferometer engineered photonic crystal fibers

In this paper, we present a numerical investigation of all-optical logic gates based on a Mach-Zehnder Interferometer (MZI) configuration of micro structured fibers, also known as photonic crystal fibers (PCF) under optical OOK (on-off keying). We determine several relevant quantities to characterize the system performance, such as transmission and extinction ratio as a function of the nonlinearity profile (β) added to one of the Mach-Zehnder Interferometer (MZI) arms. High-order effects such as third-order dispersion, intrapulse Raman scattering and self-steepening were included in the generalized nonlinear Schrödinger equation describing the pulse propagation. For this study, we used an optical pulse with a shape of hyperbolic secant of 100 fs (femtosecond). A pumped laser with three power values was simulated. With critical power Pc = 103.5 kW (P = Pc), below the critical power P = 90 kW (P < Pc) and above the critical power P = 110 kW (P > Pc). We added a nonlinearity profile in one of the Mach-Zehnder Interferometer (MZI) arms. Nonlinearity profiles were expressed in terms of the parameter β. We studied three different profiles: constant, increasing and decreasing. Our results show that the proposed device can be used to obtain all-optical OR and XOR logic gates as well as logic functions A and A.B¯. The OR logic gate was the one which achieved the greatest FOMELG (Figure of Merit of Logic Gates) when using increasing profile with critical power (P0 = 103.5 kW) for β = 1.05 and FOMELG = 15.68 dB. The XOR logic gate presented the greatest FOMELG = 7.75 dB when using the decreasing profile with power below the critical (P0 = 90 kW) for β = 1.44. These results provide support for applications in all-optical networks.