462 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 OR, XNOR, and NAND Optical Logic Gates in MachZehnder Waveguiding Structure Consisting of Nonlinear Material Muhimmatul Khoiro*, Melania Suweni Muntini, Yono Hadi Pramono Department of Physics, Faculty of Science Institut Technology of Sepuluh Nopember, Surabaya, Indonesia E-mail: [email protected]; [email protected] Abstract-OR, XNOR, and NAND optical logic gates in Mach-Zehnder waveguiding structure consisting of nonlinear material had been analyzed by means of Finite Difference Beam Propagation Method (FDBPM). Nonlinear material is assumed to be a Kerrlike material which has a refractive index changes depending on the intensity of the local electric field from the input beam power. Here we use Organosol SnO2 as film of waveguide. The Cladding is composed of linear material which has a little different with the film refractive index such as Flint Glass. The proposed waveguide is included by three input beams. Port 1 and 3 contribute as control signal which stable input power of 1 W/m and center input as input signal has varied power input value between 0 to 20 W/m. Output signal has measured just in port 5 (center output port). By investigation of the output power, the proposed structure of waveguide can generate optical logic for OR, XNOR and NAND operation. This paper represents that multi-functional devices such as OR, XNOR and NAND operation would also be possible in a single optical waveguide. Index Terms- Nonlinear material, Mach-Zehnder waveguide, optical logic gates, FDBPM. I. INTRODUCTION Along with technology advanced recently, it required ultra-high-speed signal processing device for communication and information system requirement. Devices which contain nonlinear material, can be promising solution. These materials have highly potential to be applied on super-fast optical signal switching process. This switching process has speed of a terabit per second when using fastness recombination and interaction of photons using nonlinear materials [1]. Some of nonlinear material which have high possibility for that application, is SnO2 dan TiO2 [2]–[3]. When the nonlinear materials are induced by high intensity of electric field, refractive index of the materials will change and enlarge self-focusing or self-routing in the materials. This index of refractive-dependent changes is expected to be utilized in various of optical devices to operate at high bit rates. One of the optical devices which have been widely utilizing nonlinear materials is waveguides. Nonlinear waveguides have been developed for various functions such as switching and optical logic gates on various structures of waveguides. The function of the waveguide as an optical switching is similar to the optical switching process in fiber coupling that has been done in previous research [4]. The learning of basic structure for analyzing optical switching process has been applied such as in the directional couplers, X-crossing, Y-branching, even by utilizing nonlinear uniform medium [5]–[10] . Furthermore, the waveguides are expected to be combined with other optical devices such as a combination of optical switching with antennas that have been performed in previous studies [11]–[12]. Nonlinear waveguides have also been used for many optical logic gate applications. This optical logic gate is applied to various structure of waveguide, such as symmetry X-crossing waveguide and asymmetry Y-branching waveguide and Mach-Zehnder waveguide [13]–[17]. However, each optical logic gate function is obtained by IJMOT-2018-6-1591 © 2018 IAMOT 463 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 changing the structure or parameter of waveguides. In this paper, a nonlinear waveguide is proposed for optical logic gates applications with fixed structures and parameters. The Mach-zehnder structure has two arms. If one or both arms are given pertubation effect, there will be a phase waveguide and radiation loss as experienced by using S and Y structures. The advantages of this structure is good bandwidth, smaller size, high fabrication tolerance and best balance of power [18]. This structure has better performance of sensitivity to wavelength and temperature than the structure of Microring Resonator [19]. II. CHARACTERISTICS OF WAVEGUIDE The proposed waveguide structure is composed of the waveguide shaped Mach-Zehnder with two straight control waveguide as shown in fig.1. In output regions, the separation distances are arranged by providing a certain angle (2) to avoid coupling between waveguides. It contains of nonlinear material as film/guide parts and linear material as cladding while the parameters is shown in table 1. The width of the waveguide's guide parts is equal to d1 = 2 mikrometers, except for the width in the Mach Zehnder's arms as d2=1 mikrometers. This parameter is chosen because to create a single-mode waveguides. The films of the waveguide contains a nonlinear material assumed as a kerr type materials. While the substrate of this waveguide is a homogeneous linear materials. Therefore, the refractive index of the film will change according to the intensity of the applied electric field according to the following equation: n f n 2fl E Fig.1. Proposed waveguide structure Table 1: Fixed parameter of the proposed structur of micro-ring resonator waveguide Parameter Waveguide length Mach-Zehnder’s arms length Waveguide width Straight waveguide thickness Mach-zehnder’s thickness Gap Angle of MZ branches Angle of output waveguides Refractive index of film Refrative index of cladding Nonlinear coefficient Wavelength Waveguide length of output port Value L = 4250 µm Lg = 2500 µm W = 150 µm d1 = 2,0 µm d2 = 1,0 µm g = 7,18172 µm θ1 = 1o θ2 = 0,25o nf = 2,011 nc = 2,006 α = 1,7 x 10-11 m2/V2 λ = 1,06 µm Lout = 1000 µm 2 (1) The higher intense of the electric field, the higher the refractive index when α is positive. The waveguide is also assumed to be homogeneous along the y-axis, so / y 0 . The wave equation is represented by the electric field Ey, the TE mode inside along the waveguide consisting the nonlinear Kerr-Like medium is 2 E y 0 0 n 2 2 Ey t 2 0 2 PNL t 2 (2) Where 0 and 0 is permitivity and permeability on free space and PNL is third order nonlinear polarization which given by equation: PNL 0 3 E y3 (3) In this research, organosol SnO2 material was selected as a nonlinear material which formed waveguide by refractive index, nf = 2,011 as a film IJMOT-2018-6-1591 © 2018 IAMOT 464 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 and nc = 2,006 as cladding and nonlinear coefficient α = 1,7 x 10-11 m2/V2. While the waveguide is inserted by input beam with wavelength response, λ = 1.06 µm [20]. The basic mode propagation constant, TE0 in the input port has been calculated using the numerical method as β/k0 = 2,00789266697578 (k0 is wavenumber in free space). The proposed waveguide is numerically analyzed using FD-BPM (Finite Difference Beam Propagration Method). The analyzed is made in region |x| < xmax (= 25 μm) by calculating the homogeneous grid with interval Δx = 0.05 μm in tranverse coordinate and interval Δz = 1 μm in direction of propagation. The input power is evaluated by electric field integrals generated by the iteration process along the x axis in the device area and the output power is evaluated from the thickness of each channel in the waveguide [6]. As a logic gate application, the efficiency η is only calculated on the output power of port 5 compared to the total input power given in the following equation: Pout ,5 respon at power of 5,10 W/m. It is characterized by an irregular value of output power. The lowest output power value is obtained at input power of 18,10 W/m, which is about 0,21 W/m. This indicates that on this input power, the each signal after input branch has a phase shift. The phase difference of both signals reaches the maximum. Therefore after the two signals are reunited on the output branch, both signals have interference which debilitating each other (destructive). Figure 3-6 shows the wave propagation behavior on the waveguides by input power of 18,1 W/m. These figures provide a waveguide application as function of OR logic gate, as shown in table 2. The output power is obtained with a certain value by turning on control signals from either one or both. When one control signal is applied, the signal on one of the Mach-Zehnder's arms near the straight waveguide which passed by the control signal, will be disturbed. It can interfere shift of phase signals. Thus, the phase difference of signals on both sides of Mach-Zehnder's arms doesn't reach the maximum and interference between both of them doesn't completely eliminate each other. It also happens when both control signals are given. (4) Pin 12 III. RESULT AND DISCUSSION The following figures show wave propagation on the proposed waveguides. Input beams through three ports namely ports 1, 2, and 3, where ports 1 and 3 are control signal ports that act as logic gate controls. On both these ports only have two states that state "1" if the port is given signal, and state "0" if the signal is turned off. The control signal given on ports 1 and 3 has a fixed signal power of 1 W/m. While port 2 serves as a port input signal. In this port the signal is always supplied but with the power intentionally changed. Figure 2 shows the output power characteristics when the input power is applied to the machzehnder waveguide without control signal power from both straight waveguides. The graph shows that the nonlinearity of the waveguide starts to Output Power, Pout (W/m) 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 18 20 Input Signal Power, Pin (W/m) Fig.2. Charactistics of output power when control power is turned off By turned on one of the control signals, the input signal from one of the mach zehnder's arms near the straight waveguide which is passed by the control signal, is interrupted by the pertubation between both of signals and give affect to phase IJMOT-2018-6-1591 © 2018 IAMOT 465 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 shift of the input signal. The effects of pertubati on begins to observe from the input power of 3,5 W/m where the output power value begins to decrease slightly, as shown in Figure 7. The oscillation of output power value increase on the input power above 4,2 W/m because followed by the response of nonlinearity material on waveguide. Fig.6. Propagating of light waves in the OR gate when input power in port 2 = 18,10 W/m and control signal in both ports 1 and 3 Figure 7 shows that the control signals at port 1 (straight line) and at port 2 (dashed line) have dif- Table 2: On-off states and output power for OR gate on proposed waveguide Input power Port 1 Port 2 0 0 1 0 0 1 1 1 Propagating of light waves in the OR gate when input power in port 2 = 18,10 W/m and no control signal 12 Output Power, Pout (W/m) Fig.3. Output Power (Port 5) State Power (W/m) 0 0,21 1 1,77 1 6,77 1 1,67 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 18 20 Input Signal Power, Pin (W/m) Port 1 is turned on Fig.7. Fig.4. Fig.5. Propagating of light waves in OR gate when input power in port 2 = 18,10 W/m and control signal only in port 1 Propagating of light waves in the OR gate when input power in port 2 = 18,10 W/m and control signal only in port 3 Port 2 is turned on Charactistics of output power when one of control power is turned on ferent output power characteristics. This can be due to the nonlinear material effects already embedded in the input waveguide (before branching) giving a phase shift on each part of the input signal. So the signals that divided into branches already have different characteristics, also give different responses to the disturbance of the control signals. This difference occurs only after a fairly high power input, which in this case occurs after the input power of 4 W / m. This is also the reason why the output power on the OR logic gate especially when one of port 1 and port 2 is turned on, has a pretty much different value. IJMOT-2018-6-1591 © 2018 IAMOT 466 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 The lowest output power by giving one of the control signals occurs at an input power of 15 W/m. Using the input power, the waveguide appli cation is obtained as a function of XNOR optical logic gate, as shown by the wave propagation in Fig. 8-11 while the output power values for each state are also shown in Table 3. Fig.11. Propagating of light waves in the XNOR gate when input power in port 2 = 15 W/m and control signal in both ports 1 and 3 Table 3: On-off states and output power for XNOR gate on proposed waveguide Fig.8. Input power Port 1 Port 2 0 0 1 0 0 1 1 1 Propagating of light waves in the XNOR gate when input power in port 2 = 15 W/m and no control signal Output Power (Port 5) State Power (W/m) 1 6,96 0 0,05 0 0,15 1 3,28 14 Output Power, Pout (W/m) 12 10 8 6 4 2 0 0 Fig.9. Fig.10. Propagating of light waves in the XNOR gate when input power in port 2 = 15 W/m and control signal only in ports 1 Propagating of light waves in the XNOR gate when input power in port 2 = 15 W/m and control signal only in ports 3 2 4 6 8 10 12 14 16 18 20 Input Signal Power, Pin (W/m) Fig.12. Charactistics of output power when both of control power is turned on The oscillation frequency of the output power value is greater when both control signals are turned on, as shown in Figure 12. The value of the output power has already begun to oscillate, even in a small input power of 3,4 W/m. It is due to the pertubation effect of both control signals through straight waveguides and also the nonlinear material effect which is contained on the waveguide. IJMOT-2018-6-1591 © 2018 IAMOT 467 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 Fig.13. Propagating of light waves in the NAND gate when input power in port 2 = 18,70 W/m and no control signal Fig.16. Propagating of light waves in the NAND gate when input power in port 2 of 18,70 W/m and control signal in both ports 1 and 3 Table 4: On-off states and output power for NAND gate on proposed waveguide Input power Port 1 Port 2 0 0 1 0 0 1 1 1 Fig.14. Fig.15. Propagating of light waves in the NAND gate when input power in port 2 = 18,70 W/m and control signal only in port 1 Propagating of light waves in the NAND gate when input power in port 2 = 18,70 W/m and control signal only in port 3 Figure 13-16 shows wave propagation on the waveguide with an input power of 18,70 W/m, where the output power reaches the minimum value using the input power when both control signals are turned on. However, the output power is still measurable in other states. So the waveguide can be used as a function of optical logic gate NAND, as shown in table 4. For the result shown above, it confirmed that the proposed waveguide structure could function as varied optical logic, i.e. OR, XNOR and NAND Output Power (Port 5) State Power (W/m) 1 1,37 1 4,87 1 6,28 0 0,09 operation. The operations realize just by varying power input. Here, we doesn’t need to change either waveguide structure or properties of waveguide material like previous researches. The comparation result with previous research has been shown in Table 5. The paper represent that the multi-functional device can be possible operated in a single optical waveguide. In order to allow a true comparison, we propose to compare our results and those obtained in [13]. The two studied systems have the same design except output region in our design has adjusted to avoid coupling effect between waveguides. Moreover, the two systems have difference in placed of nonlinear material. In reference [13], nonlinear material consisted just on MachZehnder’s arms. In table 5 present a comparison of optical logic gates that obtained by input power applied in waveguides. It shows a good agreement between both structures. Although both structure obtains XNOR logic application in 15W/m, the proposed waveguide can obtain another logic operation in other input power. It shows that the proposed waveguide represents multi-functional device in single waveguide. IJMOT-2018-6-1591 © 2018 IAMOT 468 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.13, NO.5, SEPTEMBER 2018 Table 5: Comparasion of results obtain for proposed structure waveguide and reference [13] Input Power Optical logic Operation References Waveguide [13] 15,00 W/m XNOR Proposed Waveguide 15,00 W/m 18,10 W/m 18,70 W/m XNOR OR NAND [3] [4] VI. CONCLUSION OR, XNOR, and NAND optical logic gates in Mach-Zehnder waveguiding structure consisting of nonlinear material had been analyzed by means of Finite Difference Beam Propagation Method (FD-BPM). The change of input power causes changeable value of the output power. Due to the nonlinearity effect on waveguides material and the perturbation effect of the control signal which through the straight waveguides, it causes different output power responses on each input power and under different states. By investigation of the output power, OR optical logic gates are obtained by input signal of 18,1 W/m, XNOR optical logic gate by input signal of 15 W/m and an optical logic NAND gate by input signal of 18,7 W/m. This paper represents that multi-functional devices such as OR, XNOR and NAND operation would also be possible in a single optical waveguide. [5] [6] [7] [8] [9] ACKNOWLEDGMENT The authors are thankful to PMDSU (Master Pogram of Education Leading to Doctoral Degree for Excellent Graduates) scholarship by DIKTI. [10] REFERENCES [1] [2] K. Al-hemyari, J. S. Aitchison, C. N. Ironside, G. T. Kennedy, R. S. Grant, and W. 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