Three-core Nonlinear Directional Coupler Research Articles

DESIGN OF AN ULTRA-FAST ALL-OPTICAL DARK SOLITON SWITCH IN A THREE-CORE NONLINEAR DIRECTIONAL COUPLER (TNLDC) MADE OF CHALCOGENIDE GLASSES

We designed and simulated a three-core nonlinear directional coupler (TNLDC) dark soliton switch. We have optimized the optical properties of chalcogenide glasses such as their high nonlinear refractive index and negative group velocity dispersion and designed a switch having a length of 7 cm and an ultra-fast pulse width of 10 fs with a 100 W power input pulse. The switching characteristic shows that complete switching is possible for different ranges of lengths and pulse widths, and by using the result of the simulation we find a relation between the length and the pulse width with respect to the necessary power for complete dark soliton switching. Also the effect of two photon absorption (2PA) on dark soliton switching was studied and it was shown that 2PA puts some limitations on the switching action but, because of the low value of the 2PA figure of merit for chalcogenide glasses, it did not have any considerable effect on dark soliton switching.

Thermal stability analysis of nonlinear optical switch based on asymmetric three-core nonlinear directional coupler with variable Gaussian coupling coefficient

We analyze the thermal stability of the power transmission efficiency and the extinction ratio in an asymmetric three-core silicon-on- insulator nonlinear directional coupler with variable Gaussian coupling coefficient. Because the refractive indices of Si and SiO2 materials are subject to temperature change, the effective refractive index of the non- linear coupler varies correspondingly. When ratio (LC/b) andT change, the relative transmission efficiency error (� ) values and relative change of extinction ratio (η) values are obtained. It can be easily shown that vari- ation ofand η are negligible under LC/b ≤ 1/2. Therefore, we can set LC/b ≤ 1/2 andT ∈ (-100 K, 100 K) in order to make the power transmis- sion efficiency and the extinction ratio work steadily. This is significant in guiding an actual nonlinear optical pulse switch fabrication. C � 2011 Society

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

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.

Logic gates based in two- and three-modes nonlinear optical fiber couplers

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 two-core 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.

Three-core nonlinear directional coupler with variable coupling coefficient

Three core nonlinear directional couplers (TCNLDCs) with variable coupling coefficients (VCCs) are proposed. Their linear operation is examined analytically. Three types of VCC TCNLDCs are investigated numerically. Their transmission features are compared with those of their two-core counterparts. It is shown that the switching curves of VCC TCNLDCs are sharper than those of their two-core counterparts. Also the features of different types of VCC TCNLDCs are compared to each other and to the constant coupling coefficient (CCC) TCNLDC. It is found that the sidelobes in the postswitching region can be suppressed with VCC TCNLDCs and the peak transmission of VCC TCNLDCs is higher.

Theory of light propagation in three-core nonlinear directional couplers

An exact analytic solution is obtained for the problem of light propagation in a three-core nonlinear directional coupler with identical parallel fibres in the geometry of a regular triangle for an arbitrary dependence of the propagation constant on the light intensity.