Simulation of All-Optical XOR, AND, OR gate in Single Format by Using Semiconductor Optical Amplifiers Chang Wan Son* a,b, Sang Hun Kim a, Young Min Jhon a, Young Tae Byun a, Seok Lee a, Deok Ha Woo a, Sun Ho Kim a, Tae-Hoon Yoon b a Photonics Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea b Department of Electronics Engineering, Pusan National University, Busan 9-735, Korea e-mail: thyoon@pusan.ac.kr ABSTRACT Using the cross-gain modulation (XGM) characteristics of semiconductor optical amplifiers (SOAs), multi-functional all-optical logic gates including XOR, AND, and OR gates are successfully demonstrated at 10 Gbps by using VPI component maker TM simulation tool. Multi-quantum well (MQW) SOA is used for the simulation of all-optical logic system. Our suggested system is composed of four MQW SOAs, SOA-1 and SOA-2 for XOR logic operation and SOA- 3 and SOA-4 for AND logic operation. By the addition of two output signals XOR and AND, all-optical OR logic can be obtained. Keywords: Semiconductor optical amplifier, all-optical logic gate, cross-gain modulation, multi-quantum well, multifunctional logic gate, optical computing. 1. INTRODUCTION As the speed of telecommunication systems increases and reaches the limit of electronic devices, the demands for digital all-optical logic operations such as switching, decision making, regenerating and basic or complex computing are rapidly increasing. In future optical signal processing and ultra-high speed telecommunication, the importance of digital all-optical processing technique such as all-optical binary logic gates are expected to become more important. The technique of digital all-optical logic operation in optical signal processing will make complicated and cumbersome electro-optic conversion unnecessary, and due to this advantage there are many researches to realize digital all-optical processing systems. As one of the key components for digital all-optical processing, many researchers use semiconductor optical amplifiers (SOAs). Comparing to techniques based on fiber, wavelengths conversion technique Optoelectronic Materials and Devices, edited by Yong Hee Lee, Fumio Koyama, Yi Luo, Proc. of SPIE Vol. 6352, 63523R, (2006) 0277-786X/06/$15 doi: 10.1117/12.691581 Proc. of SPIE Vol. 6352 63523R-1
based on SOAs are attractive because of their high-gain, high-saturation output power, wide range gain bandwidth, compactness and the possibility of integration with other semiconductor optical devices. SOAs have a wide range of functions such as amplification, switching and wavelength conversion. In addition to these applications, optical logic gates were obtained by using cross-gain modulation (XGM) characteristics of SOA [1]. XGM characteristic of SOAs is simple to implement and has shown impressive operation at ultra-high bit rates. Moreover, this shows high conversion efficiency as well as insensitivity to the polarization of input signals [2]. Our previous all-optical logic gates were single-function basic logic gates such as AND, OR, XOR, NAND, NOR and XNOR implemented for 10 Gbps systems [3-5]. However, functions handled by all-optical processing are very limited with single-function all-optical logic gates. Therefore, more complex multi-function logic systems are strongly required. In this work, we suggested and simulated all-optical multi-functional logic gates for simultaneous operation of XOR, AND, and OR gates at 10 Gbps by using commercialized program VPI component maker TM simulation tool. 2. OPERATION PRINCIPLE When electrical current is applied to the SOA, electrons in SOA placed in the excited states. The excited electrons are stimulated by incoming optical signal, and return to the ground states after signal is amplified. This stimulated emission continues as the input signal travel through the SOA until the photons exit together as an amplified signal. However, amplification of input signal consumes carriers thereby transiently reduced gain, which is called gain saturation. The carrier density changes in SOA will affect all of the input signals, so it is possible that a signal at one wavelength affect the gain of signal at another wavelength. This nonlinearity property is called XGM based on SOA and the most basic operating principle of XGM is shown in Fig. 1. The parameters of multi-quantum well (MQW) SOA which used for simulation is in table 1. The same parameters are used for the entire simulation of this study. When a pulse exists for the pump signal passing through the SOA, it causes carrier depletion in the SOA. The carrier depletion leads to gain saturation in the SOA causing a marked intensity reduction of the incoming probe signal. Therefore, a marked intensity reduction of the probe signal in the SOA leads to no pulse existence for output signal. When a pulse does not exists for the pump signal, there is no effect to the gain of probe signal in the SOA and output signal has the same pulse as the probe signal. In Fig. 1 (a), the graph in the center is saturation characteristic of MQW SOA which used for simulation when the injection current is 200 ma. When the pattern [1111] of probe signal and pump signal which has the pattern of [1010] are injected in the SOA, by the effect of gain saturation provided by the pump signal the output signal has the pattern of [0101]. And this can be the basic operation form of all-optical NOR logic based of XGM characteristic of SOA. Figure 1 (b) is simulation result of all-optical NOR logic when the pump pattern is [10101010] by using commercialized program VPI component maker TM. Proc. of SPIE Vol. 6352 63523R-2
Gain [db] Saturation Characteristic Saturation Output Power 1 1 1 1 Probe Signal (Clock) Gain -39-30 -20-10 0 10 20 25 P in (Pump) Pump [db] 0 1 0 1 Converted Signal (Output) Pump Signal 1 0 1 0 (a) Power ]mvj] 4.6 4- Clock clock Power ]mvj] 230 200 Pump SignalA 146 Output 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 O.ISAAAAAAAA 3.2 33 34 3.5 3.6 3.7 3.63.9 4 (b) -2 3.2 33 A.5A 3.7 A. 3.6 3.9 4 Fig. 1. Principle of XGM in semiconductor optical amplifier (a) Gain saturation curve and XGM operation principle, (b) NOR Simulation data Proc. of SPIE Vol. 6352 63523R-3
Table 1. Parameters of SOA for simulation Name Value Unit Norminal Wavelength 1.5525246 10-6 m Laser Chip Length 700.0 10-6 m Active Region Width 2.5 10-6 m Active Region Thickness 0.04 10-6 m MQW s Confinement Factor 0.07 Group Effective Index 0.56 Facet Reflectivity 0.0001 Optical Coupling Efficiency 1.0 Fixed Internal Loss 3000.0 1/m Linear Recombination Coefficient 0.00 1/s Bimolecular Recombination Coefficient 1.0 10-16 m 3 /s Auger Recombination Coefficient 1.3 10-41 m 6 /s Transparency Carrier Density 1.5 10 24 1/m 3 The pump signal and the probe signal can operate either in co- or counter-propagating configuration. Counterpropagation has the advantage that optical filtering of the probe signal is not required if the facet of SOA is coated for anti-reflection. In this study, counter-propagation scheme of XGM is used for the simulation of all-optical multifunctional logic gate [2]. Operation principle of multi-functional all-optical logic XOR, AND, and OR gate is shown in Fig. 2. In the XOR gate, A B is obtained by using signal B as a probe beam and signal A as a pump beam in SOA-1. Boolean A B is Boolean obtained by using signal A as a probe beam and signal B as a pump beam in SOA-2. XOR logic is acquired by adding Boolean A B and A B from SOA-1 and SOA-2. In the AND gate, Boolean A B is obtained by using the signal B as a pump beam and signal A as a probe beam in SOA-3. By passing signal A as a probe beam and A B which is obtained from SOA-3, as a pump beam through SOA-4, Boolean AB is acquired. As shown in Fig. 2, all-optical OR operation can be performed by the combination of AND logic and XOR logic. Therefore, three all-optical logic operations, such as XOR, AND, and OR can be simultaneously realized in a single format. Proc. of SPIE Vol. 6352 63523R-4
B SOA-1 A XOR Part XOR A SOA-2 B A SOA-3 B OR AND Part AB A SOA-4 AND Fig. 2. Operation principle of an all-optical multi-functional logic XOR, AND, and OR gates. 3. SIMULATION RESULT The experimental setup shown in Fig. 3 is implemented by using the software commercialized VPI component maker TM. Signal B SOA-1 Signal A XOR SOA-2 Signal A SOA-3 Signal B OR SOA-4 AND Signal Analyzer Fig. 3. Experimental setup for multi-functional all-optical logic operation Proc. of SPIE Vol. 6352 63523R-5
We made 10 Gbps input signals A and B to confirm 10 Gbps operation of multi-functional all-optical logic gate. The SOA which used for simulation is multi-quantum well operates at 1.552µm. The length of SOA is 700 µm, left and right facet reflectivity is 10-4, respectively and the injection current of SOA is 200 ma. The power of probe signals is about 2.3 mw and pump signals are about mw. To simulate XOR operation, SOA-1 and SOA-2 is used. In SOA-1, we used B signal as probe signal and A signal as pump signal and in SOA-2, probe and pump signal is reversed. By passing signal A with the pattern of 1 as a probe signal and signal B with the pattern of 0110 as a pump signal into SOA-1, Boolean obtained. Also, by switching the roles of signal A and B for SOA-2, Boolean In the case of AND gate, pattern 0 of Boolean A B with the pattern of 0010 was A B with the pattern of 0 is obtained. A B is obtained by using pattern 0110 of signal B as a pump signal and pattern 1 of signal A as a probe signal through SOA-3. Pattern 0 of Boolean AB is acquired by using A B as a pump signal in SOA-4. By adding obtained pattern 1 of signal A as a probe signal and 0 of signal XOR logic and AND logic signals, we could realize all-optical XNOR gate operated at 10 Gbps. Figure 4 shows simulation results of VPI component maker TM with coded input signals A and B, and related output signals AND, XOR, and OR. In our study, we also used Pseudo-Random Binary Sequence (PRBS) input signals A and B. In the case of PRBS input signals, we can also obtain multi-functional all-optical XOR, AND, and OR logic operation. Figure 4 shows simulation results of PRBS input signal by VPI component maker TM. To simulate XOR operation, SOA-1 and SOA-2 is used. In SOA-1, we used B signal as probe signal and A signal as pump signal and in SOA-2, probe and pump signal is reversed. By passing signal A with the pattern of [001011] as probe signal and signal B with the pattern of [111111] as pump signal into SOA-1, Boolean A B with the pattern of [100100] was obtained. Also, by switching the roles of signal A and B for SOA-2, Boolean A B with the pattern of [000000000010] is A B is obtained by using pattern obtained. In the case of AND gate, pattern [000000000010] of Boolean [111111] of signal B as pump signal and pattern [001011] of signal A as probe signal through SOA-3. Pattern [000001000] of Boolean AB is acquired by using pattern [001011] of signal A as probe signal and [000000000010] of signal A B as pump signal in SOA-4. By adding obtained XOR logic with the pattern of [101100101010] and AND logic with the pattern of [000001001] signals, we could realize alloptical OR gate with the pattern of [101111111011] operated at 10 Gbps. In this research MQW SOAs are used for simulation. In the case of real implementation, speed limitation of XGM characteristics in SOA can be overcome by using a 2 mm long SOA or a quantum dot SOA [6, 7]. There are some reports about the speed of XGM characteristic go up to Gbps. Since AND, XOR and OR are the complementary functions of NAND, XNOR and NOR, all required 6 logic functions can be achieved in a single compact system by simply adding an inverter for each function. Proc. of SPIE Vol. 6352 63523R-6
Power ]mvj] 7.5 Signal signala A Power ]mvj] 333 Signal SignaiB B 200.AA.AA.AA.A. 3.2 34 3.6 3.6 4 4.2 4.4 4.6 4.6 (a) AA. AA 3.2 34 3.6 3.6 4 4.2 4.4 4.6 4.6 (b) 110 AND signal Signal XOR Signal signal 40 20 1 3.2 3.4 J..J 3.6 3.6 4 (c) 4.2 4.4 4.6 4.6 40 20 1 3.6 6 4 2 3.2 3.4 4.4 4.6 4.6 (d) 75 OR OR Signal signal 40 3.2 34 3.6 3.6 4 4.2 4.4 4.6 4.6 (e) Fig. 3 Simulation results of coded input signal. (a) A signal, (b) B signal, (c) AND signal, (d) XOR signal, (e) OR signal Proc. of SPIE Vol. 6352 63523R-7
Signal A Power ]mvj] 250 Signal SignaiB B 200 0 0 1 0 0 1 1 0 0 0 1 0 0 1 1 150 1 0 0 1 1 1 1 0 0 1 1 1 0 0 1 M. W. 19.2 19.5 20 20.5 20.6 (a) (b) AND signal XOR signal 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 1 0 1 1 1 0 0 0 0 1 0 1 0 1 0 19.2 19.5 20.5 20.6 19.2 19.5 20 20.5 20.6 (c) (d) 90 OR signal 1 0 1 1 1 1 1 0 0 1 1 1 0 1 1 UAA ta 19.2 19.5 20 20.5 20.6 (e) Fig. 4. Simulation results of PRBS input signal. (a) A signal, (b) B signal, (c) AND signal, (d) XOR signal, (e) OR signal Proc. of SPIE Vol. 6352 63523R-8
4. CONCLUSIONS By using nonlinear gain characteristics of cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs), we successfully demonstrated all-optical multi-functional logic gates for simultaneous operation of XOR, AND, and OR at 10 Gbps with four SOAs by using VPI simulation software. REFERENCE 1. A. Sharaiha, H. W. Li, F. Marchese, and J. Le Bihan, All-optical logic NOR gate using a semiconductor laser amplifier, IEE Electron. Lett. 33(4), 323-325 (1997). 2. K. E. Stubkjaer, Semiconductor optical amplifier-based all-optical gates for high-speed optical processing, IEEE J. Sel. Top. Quant. Electron. 6(6), 1428-1435 (2000). 3. S. H. Kim, J. H. Kim, J. W. Choi, Y. T. Byun, Y. M. Jhon, S. Lee, D. H. Woo, and S. H. Kim, All-optical NAND gate using cross-gain modulation in semiconductor optical amplifiers, IEE Electron. Lett. 41(18), 1027-1028 (2005). 4. J. H. Kim, Y. M. Jhon, Y. T. Byun, S. Lee, D.H. Woo, and S. H. Kim, All-optical XOR gate using semiconductor optical amplifiers without additional input beam, IEEE Photon. Tech. Lett. 14(10), 1436-1438 (2002). 5. J. H. Kim, B. C. Kim, Y. T. Byun, Y. M. Jhon, S. Lee, D. H. Woo, and S. H. Kim, All-Optical AND Gate Using Cross-Gain Modulation in Semiconductor Optical Amplifiers, Jap. J. of Appl. Physics. 43(2), 8-610 (2004). 6. A. D. Ellies, A. E. Kelly, D.Nesset, D. Pitcher, D. G. Moodie, and R. Kashyap, Error free Gbits wavelength conversion using grating assisted cross-gain modulation in 2 mm long semiconductor amplifier, IEE Electron. Lett. 34(20), 1958-1959 (1998). 7. T. Akiyama, N. Hatori, Y. Nakata, H. Ebe and M. Sugawara, Pattern-effect-free semiconductor optical amplifier achieved using quantum dots, IEE Electron. Lett. 38(19), 1139-1140 (2002). Proc. of SPIE Vol. 6352 63523R-9