An approach for Realization of all optical NAND gate using Nonlinear Effect in Ankur Saharia #1, Astt.professer PIET & M.Tech Scholar, MNIT, Jaipur, India Email ankursaharia@poornima.org Dr. Ritu Sharma #2, Astt.professer Department of ECE, MNIT, Jaipur, India Email ritusharma.mnit@gmail.com Abstract A novel approach for of all optical NAND gate has been presented using nonlinear characteristics of Semiconductor optical amplifier and band pass filter. In this paper we are proposing a simulator setup which can be used as a component in high speed logic system. Numerous approaches were suggested to realize all-optical logic gates. These include non-linear fiber based gates such as Er-doped optical amplifier and periodically poled LiNbO3 (PPLN) & interferometric structures such as the Tera-Hertz optical asymmetric demultiplexer (TOAD). The proposed setup has been tested with 10Gbps RZ input signal for proper and stable operation under different power conditions. The bandwidth of 1555μm is used for band pass filter in order to obtain the logic output for different logic input. The above setup can also be used for realization of NOR gate with slight modifications Keywords -Cross gain modulation (XGM), Semiconductor optical amplifier (), Logic Gate,, Optisystem I. Introduction The world has been witnessing the growing scenarios of realizing all optical computers using digital optical elements. All optical logic gates are essential elements and widely used in all optical signal comparator, decision, packet switching, and communication for future all optical networks. Nonetheless, all optical processing provides an intelligent solution to avert the time consuming optoelectronic conversion in various networks. Although various approaches are being suggested to realize all optical logic gates but alloptical logic gates based on semiconductor optical amplifiers (s) are promising because they are power efficient and can be integrated. Several based logic gates have been proposed [2], using Mach Zehnder interferometer gain saturation and four wave mixing (FWM), XGM respectively. The XGM characteristics are elementary to implement and have delivered sound results at ultra high bit rates. Also, they exhibit high conversion efficiency and polarization independence to input signals [13]. In this paper a realization of all optical NAND gate using is proposed. The method to achieve alloptical processing functions is to use a nonlinear optical material where different light beams can interact. Many of the nonlinear materials has investigated, but one device has emerged as a practical solution for all optical signal processing is the. All optical processing signal is of particular interest in telecommunication applications, where the benefits of the optical approach in terms power and cost are becoming important. Most based optical logic gates employ interferometric structures requiring several s and complicating the system [1]. Logic gates based on fourwave mixing in s suffer from low conversion efficiency and polarization dependence [2]. More recently, all optical gates based on injection locking of Fabry Perot Laser diodes have also been proposed [11]. Of all the available techniques, s not only provide the gating operation but they can be used for fair amplification and efficient wavelength conversion [12]. We propose a simple & polarization independent gate composed of a single followed by an optical band pass filter (). Various logic functions can be achieved with the same setup under different operation conditions. Two pulsed control signals and a continuous wave (CW) probe are injected into the, leading to a broadened probe spectrum owing to carrier density modulation by the control signals. How different logic functions can be realized by filtering the spectrally broadened probe light is also explained in next section. II. Operation Principle A simple and polarization independent logic gate composed of a single followed by an optical band pass filter (). We can achieve various logic functions with the same setup under different operation 13
conditions but we here only limited our self to a single gate.. DATA 1 DATA2 PROBE Fig 2.1 Proposed logic Gate structure A basic setup for synthesize of logic gate is shown fig 2.1.Two modulated optical return to zero (RZ) control signal are combined with CW laser pump signal for injection into the A is an opto electronic device which can amplify an input light signal. An optical gate is composed by one or more nonlinear elements and performs a specific operation An optical gate is composed by one or more nonlinear elements and performs a specific operation. The nonlinearities in s are primarily caused by carrier density changes induced by the amplifier input signals. These nonlinearities include Cross gain modulation (XGM), Cross phase modulation (XPM), and Fourwave mixing (FWM). In an optical gate light is manipulated in order to obtain optical switching (the data in one port is transferred to another port) or signal processing operations. In general, one can control the optical properties of a signal by interacting it with another (strong) signal in a nonlinear medium. The medium properties are changed by the strong signal (usually referred to as pump or control signal) and these changes are experienced by the weak signal (usually referred to as probe signal). In this paper work we investigated the possible solutions for NAND gate functionalities by using s as basic building blocks & by exploring wavelength conversion & four wave mixing then by filtering the spectrally broadened probe light using the. As we know that NAND and NOR are the universal gates and with the help of these gates we can design any combinational circuit Block diagram of NAND gate is shown in Fig. 2.2 SIGN AL D1 SIGN ALD2 EDFA FIRST COUPLER LOGIC GATE SECOND COUPLER CW LASER EDFA Fig.2.2 Block Diagram optical NAND Gate III. Simulation Setup The simulation for NAND gate was performed using Optisystem 7.0 (official license available) a simulation based tool for designing advanced optical communication systems. The simulation setup for NAND gate is shown in Fig 3.1. The data streams D1 at wavelength 1553.05 nm and D2 at wavelength 1557.75 nm were generated by modulating the CW laser optical output by an electrical PRBS (pseudo random binary sequence) generator. These two data streams namely Data1 and Data2 were then combined using a 3 db coupler. Also, a nonlinear fiber of length 1500m was inserted into the second data stream the two different data streams were them recombined using an optical coupler and then amplified using an EDFA. Fig 3.1 Simulation setup optical NAND.An optical band pass filter with centre wavelength at 1555.40 nm (the mean of the wavelengths of Data1 and Data2) is used to select only the required spectrum of the data streams. The probe signal is also generated using a CW laser tuned at wavelength 1548.3 nm and subsequently modulated by a PRBS generator. This probe signal along with combined data stream is simultaneously fed into the using 3 db coupler. To differentiate between identical data streams, a slight delay of 99 ms incorporated before first coupler using variable delay component. In order to match the power levels of both the data streams, optical attenuators were also placed after the delay component. Inside the, cross gain modulation of carrier induced charges takes place in accordance with the changes in the data streams Data1 and Data2. An optical band pass filter centered at wavelength 1548.3 nm and bandwidth 0.5 nm selects the desired NAND operation. The parameters are required to be adjusted for optimum performance, optimized 14
parameters are shown in Table 3.2 which given the desired result shown in fig 4.2 to fig 4.5 Table 3.1 Input Power Levels S.N Signal Power Level 1 D1 0.765 mw 2 D2 0.950 mw 3 Probe Signal 0.55mW Table 3.2 Parameters S.N Parameter Value 1 Wavelength 1548 nm 2 Pump Current 0.350 A 3 Linewidth 5 Enhancement 4 Thickness 0.15 μm Fig 4.2: Time domain visualizer output of final EDFA at D1=0,D2=0,showing output signal high IV. Result & Discussion The circuit consists of optical AND gate probe pump (CW laser) combined at the second coupler as shown in Fig 2.2. the combined output of AND gate and CW laser is given as input to the, the output of AND gate is high 1only when both the data pumps are at logic 1 otherwise it is low 0, therefore output of NAND gate will be low only when both the inputs are low. Fig 4.3 : Time domain visualizer output at D1=0,D2=1,showing output signal high Fig 4.1 Spectrum analyzer at the output of second when both inputs are high Fig 4.4: Time domain visualizer output at D1=1, D2=0,showing output signal high 15
truth table obtained from the time domain analysis corresponding to input signals are as above Fig 4.5: Time domain visualizer output at D1=1, D2=1,showing output signal low So the FWM will generate at only when both the data pumps are high 1. If any of the data pump is at logic 0, output of AND gate will be low and the output power of will be corresponding to CW laser only, which will show a logic high level because the power of CW laser is filtered and amplified to get the NAND gate output. If both the data pumps are high then the generated FWM signal at will spread the power of CW laser and a lower power level is obtained at the center frequency of CW laser. Since FWM will generate only when more than one signal of different frequency is given at input of. At the input of, AND gate output and CW laser is coupled. When any/both the data pumps are at logic 0 no FWM will be generated because output of AND gate will be 0 and the output will be corresponding to the peak of CW laser Table 4.1Truth Table NAND gate S.N D1 D2 Logic 1 1 0 1(High) 2 0 1 1(High) 3 1 1 0(Low) 4 0 0 1(High) Output of AND gate is high only when both the inputs are high so the output of AND gate and CW laser will together generate the FWM signal as shown in Fig 4.1 Output of is filtered with the of center frequency of CW laser. This filtered output is amplified by linear amplifier i.e. EDFA and is again filtered with the to remove the unwanted signal. So a lower value of output power will be obtained when FWM will be generated and output will be considered as logic 0.As in the NAND logic, we have a logic high when at least one of the data input is zero V. Conclusion All optical NAND gate was successfully demonstrated by exploiting XGM behavior of. Output signal versus input signal was investigated and verified through simulation. The proposed simulation set up allows compact, simple and stable operation at 10 Gb/s. The design of other logic operations like NOR,OR, AND and XOR [9] can also be achieved with the use of NAND setup with appropriate changes in operating parameters. Hence these gates can be the key elements in nextgeneration optical networks and computing systems to perform optical signal processing functions such as all optical label swapping, wavelengthconverter, header reognition[7], parity checking[6], binary addition and data encryption.furthermore, the proposed setup of alloptical NAND gate will allow easy photonic integration for designing high level digital logic circuits e.g., half adder, full adder, flip flop etc. VI. References [1] J Y. Kim, J M. Kang, T Y. Kim, and S K. Han, Alloptical multiple logic gates with XOR, OR, NOR and NAND functions using parallel MZI structures: Theory and experiment, J. Lightw. Technol.,vol. 24, no. 9, pp. 3392 3399, Sep. 2006. [2] S.H. Kim, J.H. Kim, B.G. Yu, Y.T. Byun, Y.M. Jeon, S. Lee, D.H. Woo and S.H. Kim, All optical NAND gate using cross gain modulation in semiconductor optical amplifiers, Electronic Letters, vol. 41, no. 18, Jun. 27 2005. [3] All Optical Logic Gates Based on an and an Optical Filter z. U(i), Y. Liu(i), s. Zhang(1), H. Ju(1), H. de Waardt (1), G.D. Khoe(1) and D. Lenstra(1,2) [4].All optical logic gate using semiconductoroptical amplifier assisted by optical filter Z. Li, Y. Liu, S. Zhang, H. Ju, H. de Waardt, G.D. Khoe,H.J.S. Dorren and D. Lenstr [5] Stubkjaer, K.E.: Semiconductor optical amplifier based all optical gates for high speed optical processing,ieee J. Sel. Top. Quantum Electron., 2000,6, (6), pp. 1428 1435 [6] J. M. Martinez, J. Herrera, F. Ramos, and J. Marti, Alloptical address recognition scheme for label swapping networks, IEEE Photon. Technol. Lett., vol. 18, no. 1, pp. 151 153, Jan. 1, 2006. [7] J. M. Martinez, F. Ramos, and J. Marti, All optical packet header processor based on cascaded MZIs, Electron. Lett., vol. 40,no. 14, pp. 894 895, 2005 [8] M.J. Connelly, Semiconductor Optical Amplifiers, Kluwer Academic Publishers. [9] M. Cabezón, A. Villafranca, J.J. Martínez, D. Izquierdo, I. Garcés, J. Pozo, 4 input NOR gate using cross gain 16
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