A method for fabricating optical Directional Couplers by combining thermal and field assisted ion exchange processes is presented. Modeling, design, fabrication, and test methods are discussed. This method eliminates the need for high-resolution lithography that is needed in conventional methods of Coupler fabrication.

Wide bandwidth and high data transfer rates are essential advantages of optical telecommunication networks. Full exploitation of the benefits of optical communications requires a fully optical network. All-optical circuits are one of the main alternatives to eliminate the limits of electronic circuits and provide high-speed processing systems. This study aims to design an Majority Gate based on the Nonlinear Kerr Effect. The proposed structure includes a Directional Coupler with nonlinear rods. In the proposed structure, a nonlinear Directional Coupler is used to transmit the phase of the input signal. Also, input connections are optimized to prevent the return of light along the structure. To evaluate the operation of the proposed structures, PWE and FDTD methods are used. The effect of some parameters variation on the output power has been investigated, proving the robustness of this designed structure of Majority gate against process variation. In this simulation, the proposed structures' switching power is 3 W and the bit rate is Tbits/s.

In this paper a novel design of all-optical half-subtractor based on nonlinear Directional Coupler is proposed. By using four waveguides and appropriately adjusting the refractive indices and selecting the proper length of waveguides, halfsubtractor function can be obtained. The operation of this function is simulated by RSoft CAD-Layout (BeamPROP) simulator. The simulation results confirm the all optical half-subtractor circuit without any optoelectronic conversions.

This paper presents the analysis and design of an asymmetrical Directional Coupler (ADC) with arbitrary source and load impedances. The microstrip-coupled-line structure is analyzed and its impedance matrix is first obtained. Its transmission matrix is then determined. The transmission matrix of multi-section ADC is then obtained using its properties. Finally, the total transmission matrix is converted to the impedance matrix and then its scattering matrix is derived. The method of least squares (MLS) is applied for the design of ADC. An error function is constructed based on the scattering parameters of ADC, which is a function of its geometrical dimensions. The minimization of the error function determines its dimensions (namely widths and lengths of line sections and their spacings) by writing a software in MATLAB using the Genetic Algorithm (GA) and Conjugate Gradient Algorithm (CGM). The HFSS Full Wave Software is applied to finalize the optimum design of the ADC configuration. An example of the ADC is designed, fabricated (on the substrate ROGERS 4003) and measured as the proof of concept. Its coupling coefficient is 6 dB, frequency band is 5. 2-6. 2 GHz, terminal impedances are 50, 50, 75 and 100 Ohms.

We propose a new ring resonator side-coupled M-Z interferometer all-optical switch through the pumped nonlinear Directional Coupler. By controlling pump power P to lead the Coupler reflectivity r approaching to 1, the resonator finesse will be enhanced dramatically, and then the minimum switching power in silica-based practice devices can be obtained. As a sample, we use a nonlinear Coupler made by two erbium-doped fibers, and launch a 514.5nm-pump light into one of the cores to make the reflective- index difference between two cores. Based on the asymmetric-Coupler theory, we simulate the relationship between r and P, and show that the required pump power is only 0.8Mw for r →1.

In this paper a novel all-optical logic NAND, NOR and XOR gate based on nonlinear Directional Coupler theory is demonstrated. We use the identical structure which contains three waveguides, for designing these gates, the only difference however, is the power of inputs light beam. In other words, while a beam with 4 W/mm in power considered as logical one, the output is NAND gate and if a beam with 6 W/mm in power considered as logical one, the same output, will be represented, the NOR function. In this case, an other waveguide of the structure is represented the XOR gate. Therefore this case, shows both NOR/XOR gates simultaneously. By use of three waveguides and adjusting the refractive index of waveguides and selecting the proper waveguide length, NAND/NOR/XOR gates can be obtained. The operation of these gates is simulated by use of R soft's Beam PROP simulator.

In this paper sensitivity analysis of a wideband backward-wave Directional Coupler due to fabrication imperfections is done using Monte Carlo method. For using this method, a random stochastic process with Gaussian distribution by 0 average and 0. 1 standard deviation is added to the different geometrical parameters of the Coupler and the frequency response of the Coupler is estimated. The applied process must be done several times for converging Monte Carlo method. Therefore, a large number of simulations is reqired for the Coupler. This may take a long time if one uses High Frequency Structure Simulator (HFSS) as the simulation software. To decrease the required time of analysis, neural network model of the Coupler incnjuction with Mone Carlo is used. Results showed that the bandwidth of the Coupler, minimum return loss in passband and minimum isolation in passband won’ t be change considerably using the sepecified value of random process. The obtained results for a prototype of a backward wave Coupler is presented, which confirm the results of the sensitivity analysis.

Design and simulation of high directive waveguide Directional Couplers based on supershapes are presented, in the present paper. In order to obtain high directivity, circular holes in a conventional Coupler are equivalently substituted with supershape holes. In the frequency range from 8 to 12 GHz, the coupling values of two proposed Couplers are 19± 1 dB and 23± 2 dB and the directivities are better than 20 dB. The simulation results show that almost 20 dB improvement in the directivity can be achieved as compared to a conventional Coupler. The results are valuable for the design and development of broadband high directive waveguide Couplers.

In this paper a numerical method is presented for the optimum design of a branch – line Coupler for arbitrary power division between output ports over a frequency band together with impedance matching of the source to the four ports of the Coupler are expressed in terms of the reflection and transmission coefficients, which are themselves written in terms of the scattering parameters and finally transmission matrix parameters in the even–and odd–mode analysis. After calculation of the output powers at the four ports, an error function is constructed for the power division ratios in the desired frequency bandwidth. In the proposed design method, the dispersion models for the microstrip limes are also included. The Minimization of error function determines the Coupler dimensions such as the widths and lengths of the strip conductors.The frequency response obtained from the computer programs shows that the proposed method for the design of branch-line Couplers is effective.