Balanced hybrid and Raman and EDFA Configuration for Reduction in Span Length

Transcription

1 Balanced hybrid and Raman and EDFA Configuration for Reduction in Span Length Shantanu Jagdale 1, Dr.S.B.Deosarkar 2, Vikas Kaduskar 3, Savita Kadam 4 1 Vidya Pratisthans College of Engineering, Baramati, 2 Vidya Pratisthans College of Engineering, Baramati, 3 Bharti Vidyapeeth s College of Engineering Pune 1 shantanujagdale@gmail.com 2 sbdeosarkar@yahoo.com Abstract The detail analysis of hybrid configuration of EDFA and amplifier has found that, the use of hybrid configuration with proper gain balancing gives the advantages in terms of reduced span length and improved OSNR. In order to compare different system configurations, a weight for the impact of fiber nonlinearities has been introduced. The maximum reachable distance has been evaluated as a function of the span length and nonlinear weight, given a target optical signal-to-noise ratio. Keywords- Optical Amplifier, Wavelength Division Multiplexing, Add/drop Multiplexer, Erbium Doped fiber amplifier I. INTRODUCTION The capacity of light wave communication systems has undergone enormous growth during the last few years. Laboratory demonstration of highcapacity transmission now exceeds 10 Tbls capacity and commercial systems are capable of delivering multiterabit capacity. The transmission systems incorporate Wavelength Division Multiplexing (WDM) technique, which can offer capacities much higher than single channel alternatives. Erbiumdoped fiber amplifier (EDFA) is a key technology that enabled the deployment of multichannel WDM systems. The Raman Effect in silica fibcr has becn intensively investigated in reccnt years. Stimulated Raman scattering transfers energy from the pump light to the signal via the excitation of vibrational modes in the constituent material. Measurement of Raman gain coefficient in silica fiber has revealed that a significant amount of gain can be obtained at moderately high pump powers. Several WDM transmission experiments have been reported, which have used distributed Raman amplification in the transmission fiber to enhance system OSNR. The Raman pumping is normally implemented in a counter propagating configuration in order to avoid noise transfer from the Raman pump to the WDM signals[1]. In this paper optimal balancing between Raman and EDFA amplification has been set and system is analyzed considering system parameters such as launched power, span length and system is observed for received OSNR and impact of kerr non linearity is also been observed. System results are validated through simulations in Optical System Simulator Optsim. The experimental results [2] have shown that Hybrid Raman/Erbium-Doped Fiber Amplifiers (HFA) are an enabling and promising technology for DWDM multiterabit systems. Moreover, HFA s can be used to upgrade a system from single- to multi-channel [3] and to maximize the fiber span length in medium-haul submarine links [4]. II. ANALYSIS The system configuration used is as shown in figure 1.We Figure 1. Experimental System Configuration considered a periodical system link composed of Nspan fiber spans. Each span is Lspan long and is backward pumped to obtain a Raman on-off gain GRaman. The total link length is LTOT. Each fiber 464

2 is followed by a Flattening Filter (GFF), a Dispersion Compensator (DC), an Add/Drop Multiplexer (ADM), and finally an EDFA with gain G EDFA. We assume that the amplifier gains are set so No. of Spans EDFA EDFA & as to perfectly compensate for the loss of the passive components and thefiber in each span, yielding mode having length of 50 km and attenuation 0.2 db/km, dispersion of 0.02 ps/nm/km, kerr non linearity weight K NL =0.2 The loop is iterated for 30 times causing the length of fiber for whole configuration becomes equal to the 1500 km.. All the three configurations are simulated separately in sample mode configuration and the OSNR at the receiver side is measured The eye diagrams also studied at the receiver side using the electrical spectrum analyzer to determine the BER and Q factor, Raman flat gain profile it is pumped with following configuration. The Table 1 shown below are the results of OSNR for three different configuration for 30 spans. The gain profile for three amplifier configurations are EDFA = 25 db, = 21 db ( pump power 500mw at 1440 nm), where S is the fiber loss coefficient and T F is the loss introduced by all passive components. A Raman pump with the proper power level is injected to get the required gain G Raman.. We also assume that gains are set so as to perfectly compensate for the total loss of the link yielding. Where s and DCF are the fiber loss coefficients for the transmission and DCF fiber, respectively, and T F is the loss introduced by GFF III. RESULTS AND DISCUSSION The optimization of Raman and EDFA amplifier scheme utilizes 32-channel WDM system with data rate of 40 Gb/s is utilized. The same system is analyzed for 3 different configurations to achieve the increased OSNR and to reduce the span length. The 3 different configurations are system with EDFA amplifier, Raman amplifier and with combination of Raman and EDFA amplifier.the three different configurations are fiber following the EDFA amplifier, Raman amplifier and the combination of the Raman & EDFA amplifier(hybrid configuration). The fiber is single Table 1. OSNR Results for high gain amplifier configuration. EDFA/= 25 db/ 21 db (pump power 500mw at 1440 nm).. The graph for above table is as shown in figure 2l communication OSNR of 19 db is desirable at the receiver side, but consider here the OSNR of 30 db The calculation for this OSNR are as below Span length for Amplifier in Km = Total fibre length in km/no of spans For 30 db S`NR i) EDFA/ = 1500/10=150Km ii) EDFA = 1500/20=75 Km iii) = 1500/24 = 62.5 Km From the calculation it is clear that with the hybrid configuration we can achieve the very good OSNR and reduced span length, but what about the 465

3 Q factor and BER at receiver side. These things can be illustrated with the help of eye diagram as shown in figure 3.The eye diagrams clearly shown that for such high OSNR with gain as illustrated above the BER is and Q factor of 6 db both of these things are undesirable from the point of communication. From the eye diagram it can be clearly interpreted that the received signal is very No. of Spans 1 EDFA EDFA & poor and the sym bols can not be disti ngui shed. One of the solut ion is the proper gain balancing between hybrid configuration. Figure 3 Eye diagram for the hybrid configuration with gain EDFA/Raman = 25dB/21dB The following results are the improved version of previous with little bit gain balancing showing improved OSNR reduced BER. The table 2 is showing the values of OSNR for three different configurations, the graph is plotted for highest OSNR of 30 db. The gain profile for three amplifier configuration are EDFA = 15 db = 14 db ( pump power 300mw at 1440 nm) EDFA/= 15 db/ 9.79 db ( pump power 200mw at 1440 nm).the calculations for this configuration arespan length for Amplifier in Km = Total fibre length in km/no of spans For 30 db SNR i) EDFA/ = 1500/5=300Km ii) EDFA = 1500/24=62.5 Km iii) = 1500/18 = Km Figure 2. Plot for the OSNR vs No. of Spans for high gain amplifier configuration 466

4 Table 2. OSNR Results for reduced gain amplifier configuration. The graph for the above configuration is shown in figure 4. values of OSNR for the balanced gain configuration. The gain profile for three amplifier configurations are EDFA = 10 db,= 5 db ( pump power 100mw at 1440 nm), EDFA/= 10 db/ 5 db ( pump power 100mw at 1440 nm) No. of Spans EDFA EDFA & SNR IN DB span vs edfa span vs raman span vs raman/edfa no of spans Figure 4. Plot for the OSNR vs No. of Spans for reduced gain amplifier configuration Again from the calculation it is clear that with the hybrid configuration we can achieve the very good OSNR and reduced span length, but what about the Q factor and BER at receiver side. These things can be illustrated with the help of eye diagram as shown in figure 5.The eye diagram for reduced gain configuration are much better than that of the high gain configuration the symbols are little bit distinguishable but the Q factor and BER are still poor that means we can go for some reduced OSNR but the BER and Q factor should be within the acceptable limit.( BER= ,Q Value =6.06 db) Table 2. OSNR Results for balanced gain amplifier configuration. The graph is plotted from the above table which is as shown in figure 6. For optical communication OSNR of 19 db is desirable at the receiver side, but from graph in figure 2 and 4,it is clear that for a high OSNR such as 30 db we are achieving reduced span length but worst signal at the receiver side, hence instead of achieving such high OSNR we will just take 3 db margin over the 19 db i,e 22 db.the calculation for this OSNR are For 22 db SNR i) EDFA/ = 1500/18=83.3Km ii) EDFA = 1500/24=62.5 Km iii) = 1500/22 =68.18Km The eye diagram in figure 7 and the calculation are justifying that with proper gain balancing we can achieve reduction in spans and improved OSNR the BER is reduced one it is and improved Q factor of db. Figure 5 Eye diagram for the hybrid configuration with gain EDFA/Raman = 15dB/9.79dB The last iterated configuration is for the almost balanced gain configuration, the table 3 is showing 467

5 SNR IN db span vs EDFA span vs raman span vs EDFA/ NO OF SPANS Figure 6. Plot for the OSNR vs No. of Spans for matched gain Amplifier configuration Figure 7 Eye diagram for the hybrid configuration with gain EDFA/Raman = 10dB/5dB IV. CONCLUSION The system used is having operation in the C band ( 1530nm nm) in which main aim was to optimize the hybrid configuration of the EDFA and Raman amplifiers in order to achieve reduction in the span length and to have improved optical Span length in km OSN R Config Amplifier Configuration signal to noise ratio. The system is analyzed for the three different configurations EDFA, Raman and hybrid configuration of Raman and EDFA amplifiers and performance of the system is noted at the receiver side for no of spans. The three different configuration for EDFA, Raman and EDFA/Raman(hybrid) has been analyzed for different gain combination, from the above result table it is clear that reduction in span length with improved OSNR with good quality factor is achieved with balanced gain hybrid EDFA and Raman configuration. REFERENCES Hybrid Configuration EDFA RAMA HYBRID Q factor BER N (db) 30 db High 75 km 62.5 km 150 km db Moderate 22dB Balanced 62.5 km km 62.5 km km 300 km km [1] Govind P. Agrawal Raman Amplification in Fiber Optical Communication System Elsevier Academic Press [2] T. N. Nielsen et al., 3.28-Tb/s (82x40 Gb/s) transmission over 3x100 km nonzero-dispersion fiber using dual C- and L band hybrid Raman Erbiumdoped inline amplifiers, OFC 2000, Paper PD23.. [3] P. B. Hansen et al., Single-channel to multi-channel upgrade of 10 Gb/s transmission systems by Raman mplification, ECOC 96, Oslo, Norway [4] J. P. Blondel et al., Network application and system demonstration of WDM systems with very large spans (error-free 32x10 Gbit/s 750 km transmissionover 3 amplified spans of 250 km), OFC 2000, Paper PD31 468