Performance Investigation of Dispersion Compensation Techniques in 32-Channel DWDM System

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1 Performance Investigation of Dispersion Compensation Techniques in 32-Channel DWDM System Deepak Sharma ECE Department, UIET, MDU Rohtak Payal ECE Department, UIET, MDU Rohtak Rajbir Singh ECE Department, UIET, MDU Rohtak ABSTRACT In optical fiber communications, Dispersion Compensation is an essential phenomenon.in this paper, we have investigated a 32 40Gbps DWDM system including dispersion compensation techniques (DCT ) (pre, post and symmetrical) with NRZ modulation format. This suggested high speed DWDM system is demonstrated using a singlemode fiber (SMF), the dispersion of which is compensated with an equivalent length of (Dispersion Compensation Fiber) DCF under DCT with EDFA. The system is analyzed using OptiSys V14 Simulator. Further, the results are examined by studying Eye Diagrams and performance comparison for these DCT s are carried out in terms of Q-Factor and BER. Keywords DCT, SMF, DCF, Q-Factor, BER INTRODUCTION Optical Fiber communication offers very high band-width. For resourceful bandwidth utilization, WDM technology is used, which permits several channels to be multiplexed onto a single optical fiber. The goal of any communication is to increase the data rate and transmission distance as well. For this, it becomes necessary to study the several characteristics of optical fibers (attenuation and dispersion) that affect the performance of optical fiber communication. For reducing attenuation, EDFA, SOA and Raman amplifiers are used [1][2]. On the other hand, for an increased transmission distance and data rate, due to pulse broadening, Dispersionleads to inter symbol interference resulting an error in the symbol detection. DCF In WDM networks, DCF is an effective way to reduce the over-all dispersion. DCF s have negative dispersion coefficient which can be connected to transmitting fiber having positive dispersion coefficient, thereby overcoming the added dispersion as represented by equation (1) Dispersion (SMF) x Length (SMF) = - Dispersion (DCF) x Length (DCF)... (1) This causes the total over-all dispersion of optical communication link to be zero, after transmission of the signal through long distance of the fiber.depending on the arrangement of SMF and DCF in the link, there are three types of DCT s[3]. Pre-Compensation, in which DCF is positioned before the SMF after the optical transmitter Post-compensation, in which DCF is positioned after the SMF near optical receiver. Symmetrical compensation, in whichdcf is positioned between two equal lengths of SMFthat are adjacent to transmitter and receiver. 420 Deepak Sharma, Payal, Rajbir Singh

2 DISPERSION EFFECTS IN OPTICAL TRANSMISSION In SMF, performance is mainly limited by two main factors: Chromatic Dispersion (also called Group Velocity Dispersion), which occurs due to slight variation of refractive index of the glass depending on the wavelength of the light. Polarization Mode Dispersion, although in SMF, only one mode can travel at a time, this mode is carried with two different polarizations. Minor imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations [4][5]. This phenomenon is known asbirefringence. Mode birefringence is represented as shown in equation (2). Where = = (2) represent the refractive indices of the two orthogonal polarizations. For a given, its fast axis and slow axis components will be formed. The phase difference after the transmission of light waves at a distance of L Km is given by equation (3). φ = = ( )L = ( ) (3) If is a constant, the phase difference between fast axis and slow axis will periodically repeatthrough the light waves in transmission process. The length that leads to a phase difference of 2 or power periodic exchange is called Polarization Beat Length as represented by equation (4). = = (4) Due to refractive index difference between the two axis, the transmit rate of two polarization components will be different. Because of change in randomness of fiber birefringence, the group velocity of different polarization directions becomes random which results in the output pulse broadening. Degree of pulse broadening can be expressed by group delay as in equation (5). = = ( ) = ( + ( ) )L (5) To consider the role of SPM and dispersion, the signal transmission can be simulate by solve the nonlinear Schrodinger equation as shown below- (, ) + + (, ) (, ) (, ) + (, ) = 0 (6) After N-section dispersion compensation of DCF, the channel residual dispersion can be expressed as shown in equation (7). = N 1 + ( ) (7) is the dispersion compensation rate of p-channel. = (8) SIMULATION DESIGN We have designed a 32 40Gbps DWDM system with a frequency ranging from THz having an equal spacing of 200GHz is designed using OptiSystem 14.0 simulation software. The parameters used for simulation are shown in table 1 given below. 421 Deepak Sharma, Payal, Rajbir Singh

3 Design Components Simulation parameters Values WDM Transmitter Modulation Type NRZ Channel Spacing (GHz) 200 Bit Rate(Gbps) 40 EDFA Noise figure(db) 6 Gain(dB) 25 SMF Dispersion( ps/nm/km) 17 Length(km) 90 DCF Dispersion( ps/nm/km) -85 Length(km) 18 Low pass Bessel filter Cutoff frequency(hz) 0.75*Bit rate Table 1 Simulation Parameters The optical link comprises of SMF and DCF incorporating EDFA. The receiver comprises of a PIN diode for optical-to-electrical conversion, Low Pass Bessel Filter and a 3-R Regeneratorfor re-amplification, reshaping and retiming of data pulse.the simulation design for pre-compensation dispersion is shown in Figure 1. Figure 1: Pre-Compensation Dispersion Technique The length of DCF is 18km and SMF is 24km.We have extended the transmission distance ranging from 108km to 324km using loop control and results are obtained at 108km, 216km and 324km.For minimization of transmission losses generated by optical span and DCF, we require an optical amplifier i.e. EDFA.The simulation design for post-compensation dispersion is shown in Figure Deepak Sharma, Payal, Rajbir Singh

4 Figure 2: Post-Compensation Dispersion Technique The simulation design for symmetric-compensation dispersion is shown in Figure 3. In this technique, EDFA is used before and after the optical fiber. It provides a broad-band operation with good optical characteristics andsmooth dispersion property. Figure 3: Symmetric-Compensation Dispersion Technique RESULTS AND DISCUSSIONS We have simulated the designed setup for different dispersion compensation techniques at various transmission ranges. The figure 4 given below shows the variation of Q-factor with distance for Pre- Compensation technique. 423 Deepak Sharma, Payal, Rajbir Singh

5 Figure 4: Variation of Q-factor with distance for Pre-Compensation Dispersion Technique The table 2 given below shows the numerical values of Q-factor. From the graphical results and table 2, channel 1 provides better Q-factor as compared to Channel 16 and 32.The Q-factor decreases with increase in transmission range. Table 2: Values of Q-factor and BER for Pre-Compensation Dispersion Technique Distance Q-Factor BER Channel 1 Channel 16 Channel 32 Channel 1 Channel 16 Channel *E *E *E *E *E *E *E The variation of Q-factor with distance for Post-Compensation dispersion technique is shown in Figure 5. Figure 5: Variation of Q-factor with distance for Post-Compensation Dispersion Technique 424 Deepak Sharma, Payal, Rajbir Singh

6 Table 3: Values of Q-factor and BER for Post-Compensation Dispersion Technique Distance Q-Factor BER Channel 1 Channel 16 Channel 32 Channel 1 Channel 16 Channel *E *E *E E *E *E *E The variation of Q-factor with distance for Symmetric-Compensation dispersion technique is shown in Figure 6. Figure 6: Variation of Q-factor with distance for Symmetric-Compensation Dispersion Technique Distance Q-Factor BER Channel 1 Channel 16 Channel 32 Channel 1 Channel 16 Channel *E *E *E *E *E Table 4: Values of Q-factor and BER for Symmetric-Compensation Dispersion Technique From Table 2,3and 4 and Figure 4,5and 6, the Q-Factor for all the compensation techniques decreases with increase in transmission range.the pre- compensation techniques provides better results as compared with post and symmetric compensation. The Figure 7 given below shows the variation of Q-Factor for all three compensation techniques for Channel Deepak Sharma, Payal, Rajbir Singh

7 Figure 7: Variation of Q-Factor for Channel 1for all three compensation techniques (a) 108km (b) 216km (c) 324km Figure 8: Eye diagrams for Channel 1for Pre-compensation technique (a) 108km (b) 216km (c) 324km Figure 9: Eye diagrams for Channel 1for Post-compensation technique 426 Deepak Sharma, Payal, Rajbir Singh

8 (a) 108km (b) 216km (c) 324km Figure 10: Eye diagrams for Channel 1for symmetric-compensation technique CONCLUSION In this paper, we have investigated a 32 40Gbps DWDM system including dispersion compensation techniques (DCT) (pre, post and symmetrical) with NRZ modulation format. After comparative analysis of all three DCT s, it is found that Pre-DCT is much better and provides greater Q-factor than post and symmetrical DCT s. From simulative results it is found that by varying the number of input channels in a DWDM system, the quality of signal received at the receiving end remains almost same showingmarginal degradation and the designed system works faithfully even at higher transmission ranges. REFERENCES [1] Payal,Dr. (Col.) Suresh Kumar, Deepak Sharma, A Review of Optical Communication link design using EDFA International Journal of Enhanced Research in Management & Computer Applications, Volume 6, Issue3, March 2017pp (33-38)ISSN: [2] Payal,Dr. (Col.) Suresh Kumar, Deepak Sharma, Performance Analysis of NRZ and RZ Modulation Schemes in Optical Fiber Link Using EDFA International Journal of Advanced Research in Computer Science and Software Engineering (IJARCSSE),Vol. 7,Issue 8 August 2017,pp( ) ISSN: X DOI: /ijarcsse/V7I8/0102. [3] Deepak Sharma, Design and Analysis of a Hybrid Optical Amplifier using EDFA and Raman Amplifier, International Journal of Enhanced Research in Management & Computer Applications, Vol. 5 Issue 9, September- 2016ISSN: [4] Abhimanyu Nain, Suresh Kumar,Performance Investigation of Different Modulation Schemes in RoF Systems under the Influence of Self Phase Modulation, DG GRUYTER, Journal of Optical Communication (ISSN , ISSN (Print) DOI /joc [5] Gurpreet Kaur, Navdeep Kaur, Use of Dispersion Compensating Fiber in Optical Transmission Network for NRZ Modulation Format, International Journal Of Engineering And Computer Science ISSN: Volume 3 Issue 5, May 2014, [6] Manpreet Kaur, HimaliSarangal, Analysis on Dispersion Compensation with Dispersion Compensation Fiber (DCF), SSRG International Journal of Electronics and Communication Engineering (SSRG-IJECE), ISSN: vol. 2 issue 2, 56-59, Feb [7] M.A.Othman, M.M. Ismail, M.H.Misran, M.A.M.Said and H.A.Sulaiman, Erbium Doped Fiber Amplifier (EDFA) for C-Band Optical Communication System, International Journal of Engineering & Technology IJET-IJENS, Vol 12, No. 4, pp , [8] G. P. Agarwal, Fiber-Optic Communication Systems, John Wiley & Sons, New York, [9] G. Keiser, Optical Fiber Communication, 3 rd Ed., Mc Graw Hill, Singapore, [10] P. kaur, S. Kaur, G. Singh, Speed Enhancement of network using EDFA optical amplifier, International Journal of Electrical, Electronic and Mechanical Controls, Volume 3, Issue 1, January [11] P. Shukla, K. P. Kaur, Performance Analysis of EDFA for different Pumping Configurations at High Data Rate, International Journal of Engineering and Advanced Technology (IJEAT), Volume 2, Issue 5, June Deepak Sharma, Payal, Rajbir Singh