A. C. Ferreira

All-Optical Half-Adder Using All-Optical XOR and AND Gates for Optical Generation of “Sum” and “Carry”

Abstract In this article, a numerical simulation study using the symmetric planar three-core non-linear directional coupler, operating with a short light pulse (2 ps), for the implementation of an all-optical half-adder is presented. The half-adder is the key building block for many digital processing functions such as shift register, binary counter, and serial parallel data converters. Optical couplers are an important component for application in optical fiber telecommunication systems and all integrated optical circuits because of very high switching speeds (as high as the femto-second range). In this numerical simulation, the symmetric planar three-core non-linear directional coupler presents a planar symmetrical structure with three cores in a parallel equidistant arrangement, three logical inputs (CP, A, and B), and two output logic functions (C and S). The CP(ΔΦ) input is a control pulse with a phase difference ΔΦ = Δθπ (0 ≤ Δθ ≤ 2) between inputs A and B (logical inputs of the half-adder) and one amplitude discriminator circuit. The half-adder uses two output logic functions of Sum(S) and Carry(C), which can be demonstrated by using XOR and AND gates, respectively. For the half-adder, the phase [ΔΦMIN, ΔΦMAX] intervals are studied, allowing the operation of the device as a half-adder. For the selected range of CP(ΔΦBETTER), the extinction ratio was studied, the compression factors for both Sum(S) and Carry(C) outputs of the symmetric planar three-core non-linear directional coupler.

Realization of All-Optical Logic Gates in a Triangular Triple-Core Photonic Crystal Fiber

We propose an all-optical logical gate based in a triple-core photonic fiber crystal operating with two ultrashort fundamental soliton pulses of 100 fs, with pulse amplitude modulation in the modality of amplitude shift keying (PAM-ASK) with binary amplitude modulation. In particular, we examine the performance of a triple-core PCF coupler to execute two-input logical functions. The pulse propagation is modelled by an extended nonlinear Schroedinger equation including the terms associated with the anomalous group-velocity dispersion (GVD) and the third-order dispersion (β3), as well as the nonlinear effects of self-phase modulation (SPM), cross-phase modulation (XPM), self-steepening, and intrapulse Raman scattering (IRS) in a lossless configuration. Our results indicate the possibility of getting logical operations by controlling the phase difference between the input pulses.

A performance study of an all-optical logic gate based in PAM-ASK

In this paper a numerical study of an all-optical logical gate based in a symmetric nonlinear directional coupler (NLDC) operating with two ultrashort fundamental soliton pulses of 2ps, modulated by PAM-ASK with binary amplitude modulation to represent the logical level 1 and 0, is presented. The performance of a symmetric dual core NLDC performing two-input logical functions is examined. Initially, we evaluate the effect resulting from an increment in the PAM coding parameter offset (ϵ), considering the anomalous Group Velocity Dispersion (GVD), nonlinear Self Phase Modulation (SPM) in a lossless configuration. We can conclude that is possible to get logical operations for the cores 1 or 2 since a phase control exists which is applied to the input pulse in fiber 1.

Logic gates based in asymmetric couplers : Numerical analysis

Abstract In this work, we present a numerical investigation of the transmission and switching of fundamental solitons in asymmetric nonlinear directional couplers, constructed with dispersion decreasing fibers (DDF). In this configuration, the coupler consists of two separated parallel fibers, one with a DDF profile and the other with a constant profile. We obtained the characteristics of transmission, extinction ratio, and compression factor of the device. The truth tables for the logic gates AND, OR, and XOR were obtained. We concluded that the device presenting a constant profile provided the best performance of the studied logic gates. Logic gates AND, OR, and XOR operating with extinction coefficient around 16.6 dB were obtained.

Study of the Performance of an All-Optical Half-Adder Based on Three-Core Non-Linear Directional Fiber Coupler Under Delayed and Instantaneous Non-Linear Kerr Responses

Abstract Recently, much attention has been given to the influence of the relaxation process of the non-linear response, because the usual assumption of instantaneous non-linear response fails for ultra-short pulses, and additional contributions coming from non-linear dispersion and delayed non-linearity have to be taken into account. This article presents a numerical analysis of the symmetric planar and asymmetric planar three-core non-linear directional fiber couplers operating with a soliton pulse, where effects of both delayed and instantaneous non-linear Kerr responses are analyzed for implementation of an all-optical half-adder. To implement this all-optical half-adder, eight configurations were analyzed for the non-linear directional fiber coupler, with two symmetric and six asymmetric configurations. The half-adder is the key building block for many digital processing functions, such as shift register, binary counter, and serial parallel data converters. The optical coupler is an important component for applications in optical-fiber telecommunication systems and all integrated optical circuit because of its very high switching speeds. In this numerical simulation, the symmetric/asymmetric planar presents a structure with three cores in a parallel equidistant arrangement, three logical inputs, and two output energy. To prove the effectiveness of the theoretical model for generation of the all-optical half-adder, the best phase to be applied to the control pulse was sought, and a study was done of the extinction ratio level as a function of the Δ > parameter, the normalized time duration, and the Sum and Carry outputs of the (symmetric planar/asymmetric planar) non-linear directional fiber coupler. In this article, the interest is in transmission characteristics, extinction ratio level, normalized time duration, and pulse evolution along the non-linear directional fiber coupler. To compare the performance of the all-optical half-adders, the figure of merit of the logic gates was used. All results were obtained numerically, considering a simple model for generation of an all-optical half-adder.

All-optical nonlinear switching cell made of photonic crystal

We analyze and propose a directional optical coupler embedded in photonic crystal, which is driven by an external command signal. Therefore, this switching cell can work in an all-optical switch. The switching method uses a low-power external command signal, inserted in the central coupling region, which acts as another waveguide. The switching process is based on the change from the bar state to the cross state due to the external command signal. In our simulations we used the plane wave expansion method, finite-difference time-domain method, and our own binary propagation method.

Add-Drop Demultiplexer Operating in an Optical Michelson Interferometer Based in Fiber Bragg Gratings for Time Division Multiple Access Systems

Abstract This article presents a numerical investigation of the propagation and switching of ultra-short pulses (∼2 ps) using a fiber-optic Michelson interferometer. In this study, the performance of the Michelson interferometer is studied as a function of the non-linear characteristics of the coupler and the fiber Bragg gratings. The numerical studies were done starting from the coupled-mode equations solved using the fourth-order Runge–Kutta method. The switching characteristic of the short pulses was examined as a function of pump power and the dephasing in the reflection amplitude of one of the Bragg gratings in order to obtain an add–drop filter operation. Transmission characteristics, such as cross-talk level, extinction ratio coefficient, and compression factor, were analyzed for different dephasing values and pump powers. Pump powers were examined from below the critical power of the coupler of switching (P = 1 W), at the critical power of switching (Pc = 1.73 W), and above (P = 1.95 W). Through this study, one can verify that the transmission, cross-talk level, extinction coefficient, and compression factor depend on the pump power inserted into the device and in the dephasing. The optical fiber Michelson interferometers with identical gratings in the two output arms implement important components as a demultiplexer in add–drop devices. This device has attracted great interest in the field of all-optical switching in telecommunications for operating with high transmission rates.

High quality of logic gates from the return arm of a Sagnac fiber interferometer

Abstract In this paper, we analyze the characteristics of obtaining logic functions and logic gates in the reflected output of the Sagnac interferometer by unbalancing the interferometer through the effects of group velocity dispersion and self-phase modulation, mapped by the influence of the extinction ratio (XR) and also analyze the logic gates of better quality by proposing accuracy precision ratio (PR) defined. We studied the phase variation in the phase inserted to the input and we analyzed the related parameters of modulation. We investigated intrinsic features of reflection of the Sagnac interferometer and obtained the logic gates AND, OR, and XOR, and the logical functions ZERO, ONE, and . A specific situation happens when ρ = 0.3 and , where we find the logic gates AND, OR, and XOR. Of all results, the XOR logic gate was obtained in a greater phase variation interval. The XR had the highest contrast when ρ = 0.2 and |ɛ| = 0.028 W1/2. The proposed reconfigurable theoretical set-up gives a contribution to the design of optical networks by the analysis of the obtained logic gates and logic functions in an all-optical environment. The best quality logic gate is the AND gate presenting the |PRTOTAL| = 34.99 when .

Unbalance of the Sagnac interferometer through nonlinear asymmetry

ABSTRACT In this work, we studied the behavior of Sagnac interferometer powered by a CW signal and under the nonlinear effects of self-phase modulation, cross-phase modulation, and Raman, in two configurations (balanced and unbalanced) and five scenarios (by varying the value of the Raman fraction). In the balanced configuration, we observed that the presence of Raman effect in the loop changes the curves of transmissivity and reflectivity of the device, but only the components generated by the Raman effect (Stokes waves) are switched to the transmitted port. In the unbalanced configuration, we obtained an oscillating behavior as for transmissivity and reflectivity, which breaks the characteristic of nonlinear fiber mirror, thus enabling the transmission of the pumping wave for certain combinations of values of input power and Raman fraction.

Numerical analysis in triangular and planar three-core nonlinear optical fiber couplers (TNLDC) operating logical gates

In this paper, we investigate the switching process in triangular symmetric and planar symmetric three-core nonlinear fiber coupler (TNLDC) and we have numerically shown, via the coupled nonlinear Schrodinger equations (NLSEs), that logic gates AND, OR and NXOR can be constructed from a triangular TNLDC while the planar TNLDC produced logical gates AND, NAND, OR, and XOR. We consider two basic models. The first, one triangular symmetrical structure with three cores in an equilateral-triangle arrangement and using a control signal (CS) applied to the first core and the second model present a transverse symmetrical structure with three cores in a parallel equidistant arrangement (or planar symmetrical structure), however the position of the control signal (CS) is applied to the input of the first fiber (core 1). 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. In comparing the performance of both switches operating as logic gates we will use the figure-of-merit of the logic gates [FOMELG(dB)] defined as a function of the extinction ratio of the gate outputs.