C. S. Sobrinho

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.

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.

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.

Optical Logic Gates Using Nonlinear Directional Coupler under Pulse Position Modulation

The implementation of optical logic gates in nonlinear fiber directional coupler is investigated numerically in soliton regime. The study shows that with a proper phase control it is possible to accomplish logical operations.

Signal coupling in nonlinear hybrid optical structures: A numerical approach

The numerical study of intensity-dependent picosecond solitonic pulse coupling in nonlinear fiber grating couplers, configured with in-phase or out-of-phase uniform Bragg gratings, is reported in the present work. The time domain non-linear coupled-mode equations that model the coupling dynamics in the devices under investigation are solved numerically by the choice of a fourth-order modified predictor-corrector method. The switching performance of the devices have been investigated as a function of the input power. Characteristically, the coupling effect is dependent on the operational power level, geometry, and, in particular, the mismatching between the adjacent gratings. In the linear regime, the numerical results indicate that the relative shift of the gratings can strongly modify the reflectivity of the optical modes, impacting on the extraction efficiency. As the intensity of the input pulses increases, the hybrid character of the devices vanishes, being the coupling results very similar, independently of the proposed arrangement.