International Journals of Advanced Research in Computer Science and Software Engineering ISSN: 2277-128X (Volume-7, Issue-8) a Research Article August 2017 Performance Analysis of NRZ and RZ Modulation Schemes in Optical Fiber Link Using EDFA Payal *, Dr. (Col) Suresh Kumar, Deepak Sharma ECE Department, UIET, MDU, Rohtak, Haryana, India DOI: 10.23956/ijarcsse/V7I8/0102 Abstract Dense Wavelength Division Multiplexing (DWDM) is the current area of interest to exploit the bandwidth offered by optical fiber to enhance the data rate requirements. In the present paper analysis of DWDM system using Erbium Doped Fiber Amplifier (EDFA) is carried out in C-band. The 32-channel Wavelength Division Multiplexing (WDM) system, with a high-performanceflowrate of 10 Gbps, has been evaluated. The performance of Return to Zero (RZ) and Non-Return to Zero (NRZ) modulation formats in an optical communication system are investigated by modeling an optical fiber link using software OPTISYS V14. According to the modulated outputs, a comprehensive comparison in terms of Q factor is developed to establish the advantages and disadvantages of the code formats NRZ and RZ in short and long haul optical fiber communication system. Optimum results of Bit Error Rate (BER) and Q- factor are obtained for 60, 80 and 100km of fiber length. Pumping is discussed at 980nm and 1480nm. Keywords EDFA, WDM, DWDM, NRZ, RZ, BER I. INTRODUCTION Optical Fiber Communication is growing rapidly from the last two decades providing large bandwidth and high-speed data transmission capabilities. The signal undergoes numerous losses i.e.tap losses, splice losses, attenuationetc. in an optical fiber communication link. Because of these losses,the strength of signal drastically reduces which makes the detection difficult at the receiver. For signal transmission over longer distances in a fiber, it is required to compensate for all limitations due to which the signal strength is affected [1].The Optical amplifiers amplify the signals in optical domain thereby providing a new way of subsequent research into technologies allowing transmission over longer distances at high flow rates. The optical amplifiers are classified based on their application into two categories: Semiconductor optical amplifier and fiber amplifiers. EDFA, Raman amplifier and Brillouin amplifier belongs to the category of fiber amplifiers [2]. In EDFA, a large number of signal channels are incorporated. For further capacity upgradation of installed links, WDM is employed. DWDM is the fundamental technology of optical communication [3][5]. It works by combination and transmission of numerous signals concurrentlyat dissimilar wavelengths on a similar fiber. This technology makes manifold virtual fibers, thus enlarging the capacity of medium. Isolation amongdissimilar wavelength channels holds well as long as theoptical power of all the channels in the fiber is satisfactorily low to prevent nonlinearities and chromatic dispersion. These factors are of great concern as they limit the overall efficacy of the system [6][7][8]. II. EDFA BASED OPTICAL COMMUNICATION LINK Optical amplifiers are the critical technology for the optical communication networks, enabling the transmission of many terabitsof data over longer distances by overcoming the fiber loss limitation. EDFA being the first optical amplifier has resulted in dramatic growth in transmission capacity with the deployment of WDM systems. Fig. 1 Proposed Block Diagram of EDFA based optical communication link www.ijarcsse.com, All Rights Reserved Page 161
Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) EDFA is an optical repeater device utilized to boost the intensity of optical signals being carried through optical fiber communication systems. The Erbium-doped fiber (EDF) is at the core of EDFA technology,which is a silica fiber doped with erbium. Figure 1shows block diagram of EDFA based optical communication link comprising of three sectionstransmitter section, channel section and the receiver section. In the transmitter section, multiple signals are simultaneously combined and transmitted at different wavelengths on the same fiber. Within EDFA, an erbium-doped optical fiber at the core is pumped with light from laser diodes. Signal amplification takes place when Er +3 ions are excited by the pump source. Isolators are positioned on both ends in the channel section to function like diodes which prevent signals from moving in more than one direction. In the receiver section, dissimilar wavelengths are separated with the help of a de-multiplexer for the receiver channels[10][11][12] III. WORKING PRINCIPLE OF EDFA EDFA works on the principle of stimulated emission. When erbium is illuminated with energy at an appropriate wavelength (either 980nm or 1480nm), it is motivated to a long-lifetime intermediate state, then it decays back to the ground state emitting light within the 1520-1570 nm band [14][15]. Three energy levels E1, E2, E3 are the ground, intermediate and upper state levels respectively as shown in Fig. 2 given below. Pumping at 980nm wavelength causes erbium atoms to pass through an unstable short lifetime state before rapidly falling to a quasi-stable state. Another pumping at 1480nm wavelength causes erbium atoms to move only in between intermediate and lower stage. If some light energy already exists within the fiber, the decay process is stimulated thus resulting in amplification. Fig. 2 Energy levels and working principle of EDFA [3] Let N u, N m and N g denote the population of upper, middle and ground states. If W p represents the pumping rate, W s represents the absorption rate of photons from the signal and τ ij represents the lifetime of spontaneous emission from state i to state j,we can write the following rate equations: dn g dt = N m + W τ s N m N g W p N g N u 1 mg dn m dt = N u W τ s N m N g 2 um dn u dt = N u + W τ p N g N u 3 um Population inversion implies that N m >N g. For steady state conditions, the time derivatives disappear. As the lifetime of state u is much lesser than the lifetime of state m, the population of excited state is essentially given by the Boltzmann distribution: N u = N m e E u E m kt = βn m 4 whereβ = e E u E m kt From equation (1), for steady state conditions, we have N m + W τ s N m N g W p N g N u = 0 mg which can be simplified using equation (4) to give the inversion level as n = N m W p + W s τ = N m N g W p τ 1 β 1 The inversion level is thus associated with both the pump and signal powers and also with the pump wavelength through the Boltzmann factor. The factor β explains why 980 nm pumping is more effective in achieving population inversion than 1480 nm pumping. Though pumping with 1480 nm is used and has an optical power conversion efficiency which is greater than that for 980 nm pumping, the latter is preferred because of the following advantages it has over 1480 nm pumping. It provides a broader separation between the laser wavelength and pump wavelength. 980 nm pumping gives a lesser amount of noise. Unlike 1480 nm pumping, 980 nm pumping cannot stimulate back transition to the ground state. www.ijarcsse.com, All Rights Reserved Page 162
Q-FACTOR Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) IV. SIMULATION SETUP Fig. 3 Designed System Layout for Simulation Optical communication system as shown in Figure 3 above has been designed using software OPTISYS V14. We have simulated a 32-channel DWDM system ranging from 1527.99-1552.52nm. Simulation Setup is shown in Fig. 3. The 32 multiplexed channels simulated in this range can be changed to analyze the system performance for varying wavelength. Frequency spacing among various channels is set to 0.8 nm. The isolators are employedtoblock the reflected light into the amplifier, thus provides a stable amplifier operation. Low Pass Bessel Filter is used to confine the noise power. Results are obtained at BER Analyzer. V. RESULTS The analysis of designed optical link was performed using OPTISYSTEM simulator based upon several qualitative parameters. The parameters used in simulations are shown in the table given below. Table I: Parameter values of simulation setup Parameters Values (units) Pump Laser Frequency 980nm, 1480nm Power of Each channel 12dBm Modulation Format NRZ, RZ Fiber length 60,80,100 km Bessel filter cutoff frequency 0.75*Bit rate(hz) Gain Of EDFA 25dB Channel Spacing 0.8nm We have focused on the Q- factor of RZ modulation and NRZ modulation at 980nm and 1480nm pumping wavelength and analyzed that overall RZ modulation has greater Q-factor as compared to NRZ modulation format over various distances. Fig. 4 shows the variation of Q-factor with fiber length for RZ and NRZ. 12 10 V A R I A T I O N O F Q - F A C T O R W I T H M O D U L A T I O N S C H E M E A N D P U M P I N G W A V E L E N G T H 8 6 4 2 0 6 0 K M 8 0 K M 1 0 0 K M FIBER LENGTH (KM) NRZ with 980nm RZ with 980nm NRZ with 1480nm RZ with 1480nm Fig. 4Variation of Q-factor with Fiber length www.ijarcsse.com, All Rights Reserved Page 163
Q FACTOR Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) Fig. 5 shows the variation of Q-factor for three channels viz. channel 1, channel 16 and channel 32 with optical fiber length. As the length of optical fiber increases, with the increase in the number of channels Q-factor decreases. 12 V A R I A T I O N O F Q - F A C T O R W I T H O P T I C A L F I B E R L E N G T H F O R D I F F E R E N T C H A N N E L S 10 8 6 4 2 0 6 0 K M 8 0 K M 1 0 0 K M OPTICAL FIBRE LENGTH(KM) Channel 1 channel 16 channel 32 The graphical results shown above are tabulated as below. Fig. 5 Q-factor versus optical fiber length Table II: Q-Factor and BER for NRZ and RZ Modulation with Fiber Length for Different Channels at 980 NM Pumping Wavelength Channel Number Fiber Length Q Factor BER (km) NRZ RZ NRZ RZ Channel 1 60 5.42031 11.2177 2.56858E-08 1.50549E-29 80 5.15918 9.85584 1.01959E-07 2.96465E-23 100 2.98658 8.20904 0.00126845 0.5097E-16 Channel 16 60 4.70001 7.99506 1.20919E-06 6.22816E-16 80 4.24013 6.67892 1.04295E-05 1.6772E-11 100 3.11694 2.86598 0.000908495 0.00207496 Channel 32 60 3.76415 5.62599 7.87192E-05 9.08704E-09 Table III: Q-Factor and BER for NRZ and RZ Modulation with Fiber Length for Different Channels at 1480 NM Pumping Wavelength Channel Number 80 3.35534 4.41149 0.000373926 5.0958E-06 100 3.28883 2.62064 0.000499761 0.00436909 Fiber Length (Km) Q Factor In Fig. 6, variation of Q-factor for channel 1 is shown with different data rates. As the data rate increases, Q-factor starts degrading. www.ijarcsse.com, All Rights Reserved Page 164 Ber Nrz Rz Nrz Rz Channel 1 60 5.43525 10.9643 2.34494e-08 2.48253e-28 80 3.26346 10.0772 6.000509875 3.12018e-24 100 2.92832 8.34038 0.00150192 3.44148e-17 Channel 16 60 4.82091 8.79963 6.67789e-07 1.56526e-19 80 4.31883 7.16589 7.33623e-06 3.74891e-13 100 3.07595 2.81446 0.00103868 0.00244133 Channel 32 60 3.94053 5.77006 3.87601e-05 3.8965e-09 80 3.37838 4.65698 0.000345955 1.58937e-06 100 3.19557 2.5874 0.000694779 0.00483508
Q-factor Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) 35 30 25 20 15 10 5 0 VARIATION OF Q-FACTOR WITH DATA RATES 5Gbps 10Gbps 15Gbps Data Rate(Gbps) channel 1 Fig.6 Q-factor variation for channel 1 for Data rates The system performance was evaluated by means of BER analyzer. The Eye diagram with RZ modulation gives a larger eye opening as compared to NRZ. The width of opening shows the time over which sampling for detection is performed and the optimum sampling time corresponding to maximum eye opening yields the greatest protection against noise. Fig. 7shows the Eye diagrams for RZ and NRZ modulation schemes at 60km optical fiber length. Fig. 7 BER Analyzer for 60km Optical Fiber length From the diagram, it can be analyzed that the eye configuration for channel 1 provides a large opening which means that the inter-symbol interference (ISI) is low. Also, the system Q- factor using RZ modulation format is more than NRZ format and also long distance communication is achieved using RZ. www.ijarcsse.com, All Rights Reserved Page 165
Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) Fig.8 BER Analyzer for 80km Optical Fiber length Fig. 8 shows the Eye diagrams for RZ and NRZ modulation schemes at 80km optical fiber length. The Eye diagrams for RZ and NRZ modulation schemes at 100km optical fiber length are shown in Fig. 9. For 60 and 80 km of fiber length, with NRZ modulation format the Q-factor variation is almost the same for channel 1, 16 and 32. It decreases for 60 and 80km of fiber length. Whereas for 100km fiber length, the Q-factor increases from channel 1 to channel 32. With RZ modulation format, the Q-factor varies almost the same for 60, 80 and 100 km of fiber lengths. Fig. 9 BER Analyzer for 100km Optical Fiber length www.ijarcsse.com, All Rights Reserved Page 166
Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) VI. CONCLUSION In this paper, we have designed and analyzed a 32-channel DWDM system based on parameters- BER andq-factor over NRZ and RZ modulation format atfiber lengths- 60km, 80km and 100km.The values of Q-factor areobtained as 11.217, 9.855 and 8.209 for RZ modulation and 5.420, 5.159 and 2.986 for NRZ modulation for fiber lengths of 60km, 80km and 100km respectively. The values of BER are obtained in the range of 10-29,10-23 and 10-16 for RZ modulation and 10-8, 10-7 and 10-3 for NRZ modulation for fiber lengths of 60km, 80km and 100km respectively. On the basis ofsimulation, it was found that the value of Q-Factor decreases and BER increases with increasing fiber length. The designed system depicts significant improvement and works optimally for RZ modulation format at100km fiber length. REFERENCES [1] Payal, Dr. (Col.) Suresh Kumar, Deepak Sharma, A Review of Optical Communication link design using EDFA International Journal of All Research Education and Scientific Methods (IJARESM) ISSN: 2455-6211, Volume 5, Issue 3, March 2017. [2] M. M. Ismail, M.A. Othman, Z. Zakaria, M.H. Misran, M.A. Meor Said, H.A. Sulaiman, M.N. Shah Zainudin, M. A. Mutalib, EDFA- WDM Optical Network design System, Elsevier, Procedia Engineering 53,294-302, 2013. [3] Bhumika A. Patel, Prof. Ankit Patel, Performance Analysis of Optical Link using EDFA IJSRD - International Journal for Scientific Research & Development Vol. 3, Issue 03, 2015. [4] MishalSingla, Preeti, Sanjiv Kumar, Comparative analysis of erbium doped fiber amplifier (EDFA) based 64 channel wavelength division multiplexing (WDM) systems for different pumping techniques, International Journal of Scientific & Engineering Research, Volume 5, Issue 6, June2014. [5] 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. 2017 (ISSN 2191-6322, ISSN (Print) 0173-4911.DOI 10.1515/joc-2016-0155. [6] Kamalbir Kaur, Kulwinder Singh, Performance analysis of 16-channel WDM system using Erbium Doped Fiber Amplifier,International Journal of Engineering and Innovative Technology (IJEIT) Volume 3, Issue 6, December 2013. [7] Usman J Sindhi, Rohit B Patel, KinjalA Mehta and Vivekananda Mishra, Performance analysis of 32channel WDM system using erbium doped fiber amplifier, International journal of electrical and electronics engineering and telecommunication(ijeetc), April 2013. [8] Sachin Dev, Col.(Dr.) Suresh Kumar Dispersion Compensation in Optical Fiber Communication using Bragg Grating republished in International Journal of Engineering Technology Science and Research (IJETSR),ISSN 2191-6322Volume 3, Issue 9 September 2016,pp 35-41 [9] Neha, Dr. Suresh Kumar Role of Modulators in Free Space Optical Communication International Journal of Engineering Technology, Management and Applied Sciences (IJETMAS)ISSN 2349-4476 September 2016. [10] Dinesh Birdi, Mandeepsingh, Performance Analysis of EDFA Amplifier for DWDM System using RZ, International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering Vol. 4, Issue 7, July 2015. [11] Abhimanyu Nain, Suresh Kumar and Shelly Singla, Impact of XPM Crosstalk on SCM-Based RoF Systems Journal of Optical Communication 2016,(ISSN 0173-4911) DOI 10.1515/joc-2016-0045. [12] Giridhar Kumar R, Iman Sadhu, Sangeetha N Gain and Noise Figure Analysis of Erbium Doped Fiber Amplifier by Four Stage Enhancement and Analysis, International Journal of Scientific and Research Publications, Volume 4, Issue 4, April 2014. [13] G. P. Agarwal, Fiber-Optic Communication Systems, John Wiley & Sons, New York, 1997. [14] G. Keiser, Optical Fiber Communication, 3 rd Ed., Mc Graw Hill, Singapore, 2000. [15] Deepak Sharma, Design and Analysis of a Hybrid Optical Amplifier using EDFA and Raman Amplifier, International Journal of Enhanced Research in Science, Technology & EngineeringISSN: 2319 7463 Vol. 5 Issue 9, September-2016 [16] AvizitBasak, MobasseerM. Hossain & Md. Rakibul Islam, Performance Analysis of Erbium-Doped Fiber Amplifier in Fiber Optic Communication Technique, Global Journal of Researches in Engineering Electrical and Electronics Engineering Volume 13 Issue 6 Version 1.0 Year 2013. [17] 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. 48-50, 2012. [18] Simaranjit Singh, R.S. kaler, Hybrid Optical amplifiers for 64X10 Gbps dense wavelength division multiplexed system, Elsevier, Optik 124, 1311-1313, 2013. www.ijarcsse.com, All Rights Reserved Page 167
Payal et al., International Journal of Advanced Research in Computer Science and Software Engineering7(8) [19] A. García-Pérez, J. A. Andrade-Lucio, O. G. Ibarra-Manzano, E. Alvarado-Méndez,,M. Trejo Duran and H. Gutierrez Martin Modulation Formats for High Bit-Rate Fiber Transmission. Vol. 16 no. 2 Mayo-Agosto 2006. [20] V. Bobrovs, J. Porins, G. Ivanovs,Influence of Nonlinear Optical Effects on the NRZ and RZ Modulation Signals in WDM Systems, ISSN 1392 1215 SIGNALŲ TECHNOLOGIJA 2007. Nr. 4(76) [21] Neha, Dr. Suresh Kumar Free Space Optical Communication a Review International Journal of Electronics, Electrical and Computational System (IJEECS) ISSN 2348-117X Volume 5, Issue 9 September 2016. www.ijarcsse.com, All Rights Reserved Page 168