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In this paper we did a study of logic gates obtained in the operation of a three-core non linear directional coupler (TNLDC) and an asymmetric two-core coupler (DNLDC) operating in the CW regime (the laser signals have the same wavelength). The symmetric three-core coupler (TNLDC), with their cores identical, in a planar arrangement, was studied using a control pulse applied to the first core. The second structure is an asymmetric twocore coupler (DNLDC). Looking at the transmission characteristics of the device, through the direct and cross channel, we did a study of the extinction ratio (Xratio) of these devices. For both devices we did a numerical investigation with the objective to implement logic gates. The DNLDC supplied AND, OR and XOR gates while the TNLDC supplied AND, NAND, OR, XOR and NOT gates. In comparing the performance of both switches operating as logic gates (DNLDC and TNLDC) we define, for the first time, a figure-of-merit of the logic gates (FOMELG). In this criteria the FOMELG is defined as a function of the extinction ratio of the gate outputs. Comparing the same gates of the three and two-core NLDC we observe that the logical gates of the three-core TNLDC present a better performance than the one of the two-core DNLDC considering the figure of merit FOMELG, besides the fact that is simpler to fabricate a symmetrical coupler (with identical cores) comparing with an asymmetric coupler. We believe that the use of this figure of merit will be useful in the study of the performance of logic gates to be used in communication systems.

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In this work, we present a numerical investigation of the asymmetric double nonlinear coupling of photonic crystal fibers in an on‐off switch to obtain fully optical logic gates. Ultra‐short pulses (100 fs) are propagated through the device in three distinct excitation power regimes, power below critical (Po = 72 kW, where Po represents the excitation power of the device), critical power (Pc = 103.5 kW, where Pc represents critical Power for which the power switching is 50% for both guides. There are cases where Po is above the critical value, there are cases that is below), and power above critical (Po = 110 kW). The pulse switching characteristics are analyzed as a function of the input power and the nonlinearity profile (β‐beta) inserted in one of the component guides. The nonlinearity profiles follow the regimes: constant, increasing and decreasing, and high order effects, such as third‐order dispersion, intrapulse Raman scattering and self‐steepening are included in the generalized Schrödinger nonlinear equation governs the pulse propagation dynamics. The results show that the proposed device can be used to obtain AND, OR, and NOT logic gate. Numerical studies were done from the coupled‐coupled equations solved using the fourth‐order Runge‐Kutta method, using MATLAB as a programming tool for solving equations. The implementation of fully optical logic gates tends to revolutionize new digital systems in the field of data storage, such as optical memory, “replacement” of electronic circuits among other applications. Optical systems have a great advantage as they are free from electromagnetic interference and have high rates of data transmission.