Performance Investigation of RAMAN-EDFA HOA for DWDM System (Received 17 September, 2016 Accepted 02 October, 2016) ABSTRACT Neha Thakral Research Scholar, DAVIET, Jalandhar nthakral9@gmail.com Earlier to transmit data over longer distances effectively and efficiently, a number of techniques like data modulation formats and multiplexing were used, but still the requirement of transmitting additional data using optical networks has not been fulfilled. In this aspect to transmit additional data a hybrid configurations of optical amplifiers has been proposed by few researchers. In this paper, the performance of 100 X 10 Gbps channel DWDM - RAMAN EDFA hybrid optical amplifier system is reported with channel spacing variation having frequency range of 187.5 THz to 190.975 THz. The performance of the proposed system is investigated on the basis of BER, Q-factor, Eye closure and Crosstalk. Further the performance of this system is also reported by varying transmission distance as well as input optical power. Keywords DWDM, EDFA, RAMAN, BER, Q factor, Crosstalk 1. INTRODUCTION WDM is a technology that is used in the 1980s to transmit the data using optical fiber communication system. As the demand of transmitting more and more information occurred, there came the need to develop a system that can carry large number of independent channels having their own respective wavelength onto a single fiber. For this, DWDM technology is introduced [1]. But the strength of the signals reduced after covering some transmission distance. To overcome this problem, optical amplifiers like EDFA, Raman and SOA are started using in the DWDM system. EDFA being a doped amplifier has the capability to amplify multiple channels simultaneously and can provide high gain but they cannot provide the gain flatness due to ASE noise [2]. RAMAN amplifiers have the ability to improve the gain flatness and noise figure but the RAMAN gain gets affected due to splices and micro bend losses. [3]. Also these amplifiers when individually used suffer from various non- linearities. Love Kumar Assistant Professor, DAVIET, Jalandhar er.lovekumar@gmail.com Keeping these non-linearities in mind, a DWDM system has been developed using different combinations of optical amplifiers known as HOA. The drawbacks of one amplifier can be improved by other thus overall improving the system performance in terms of gain flatness and low BER. In literature, a lot of work has been done to improve the performance of DWDM system using HOA. Pradeep kaur et al [7] investigated the performance of EDFA-RAMAN HOA by using different input powers, different pump powers and by changing effective iteration area. To get the minimum BER and better gain, they used 2-channel DPSK modulation format. Cai et al [6] used 16 QAM multidimensional coded modulation channels and achieved 54 Tbps capacity after ~9150 km and 534 Pbps*km capacitydistance product after~10,230 km distance. Shienkuei-Liaw et al [5] proposed a set up in which they used C-band EDFA and L-band RAMAN fiber amplifier in a bridge type configuration and also used fiber bragg grating to obtain a flat gain by reducing gain variation from 6.5 db to + 0.2 db. Zhang et al. [8] designed a set up to achieve higher capacity at the receiver end. For this they designed the set up having cut off shifted single mode fiber with the cladding depressed. The fiber has the attenuation value of 0.182dB/km & an average chromatic dispersion equal to 20.2ps/nm/km. Two pumps are used for Raman having pump wavelengths of 1425 nm & 1489 nm with the pump powers of 390 mw and 580 mw resp. along with 980 nm pump wavelength and 440 mw pump power for EDFA. At the receiver end, 34.6 Tbps capacity is achieved using this set up. Zhang et al used the multiple pumps for Raman, but it becomes difficult to find the gain value in case of multiple pumps because the system become complex. This paper is organized into 3 sections. In section 1, basic introduction about hybrid optical amplifiers and their historical development is given. In section 2, the designed optical simulation setup of 100 X 10 Gbps DWDM system using RAMAN-EDFA HOA having 1
frequency range 187.5 THz-190.975 THz is shown and its performance is investigated. Section 3, gives the conclusion of the results obtained after simulation. II. SIMULATION SETUP AND RESULTS The experimental setup consists of 100 X 10 Gbps DWDM systems operating in the frequency range of 187.5THz-190.975THz. The transmitter section consists of pseudo random bit sequence generator that supplies 10 Gbps data to the NRZ pulse generator. Each channel is having its own PRBS generator to generate a random sequence of bits. Pattern of any signal does not match with each other. The outputs from NRZ pulse generator and laser Source is applied to the amplitude modulator for modulation purpose so that the signal can be transmitted over longer distances. Each CW laser has a line width of 10 MHz. After this process, all the signals are multiplexed using Wavelength Division Multiplexer. The diagram of the subsystem of transmitter array is shown below in figure 1. The parameters used for RAMAN and EDFA amplifiers are shown below in the table1 & table 2 resp. EDFA is used after the RAMAN amplifier so that the gain saturation could takes place in the EDFA and the gain of RAMAN amplifier could remain constant. After amplification, the signal is transmitted over an optical fiber having attenuation of 0.2 db/km. At the end, it is desired to convert the optical signal back into electrical signal. The optical receiver consists of PIN photodiode, Low pass filter and a 3R generator. The PIN photodiode has the responsivity of 0.875 A/W and 0.1 NA of dark current. The cutoff frequency of low pass filter used here is 7.5 X 10 +9 Hz with 0 db insertion loss. Fig 1: Transmitter Array (Subsystem) The designed system model is shown below in figure 2. For this simulation set up, effect of change in channel spacing on crosstalk, effect of varying the transmission distance and effect of change in input power has been investigated. Table 1: Specifications used for RAMAN amplifier Parameter Length Attenuation Value 12 km 0.2 db/km 2
QUALITY FACTOR Temperature Upper pump reference Noise bin spacing Pump laser frequency Pump power 300 K 1500 nm 0.1 nm 1453 nm 500 mw Parameter Gain Power Noise figure Value 25 db 100 dbm 4dB Table 2: Specifications used for EDFA Fig 2: Designed system model of DWDM system using RAMAN-EDFA HOA A. The effect of change in channel spacing To observe the effect of change in channel spacing, a set up of 100 X 10 Gbps DWDM system having 187-190.975 THz frequency range using RAMAN-EDFA HOA is designed. An input power of 3 mw is used for each continuous wave laser. The line width considered here is 10 MHz. Three channel spacings 0.2 nm, 0.1 nm and 0.05 nm are used and the performance is observed in terms of quality factor, BER, and crosstalk at 187.5 THz, 188.56 THz and 190.975 THz and the values obtained are shown graphically with the help of Matlab software. Figure 3, 4, 5 & 6 shows the obtained values of quality factor, BER, Eye closure and crosstalk respectively. 60 50 40 30 20 10 0 0.05 0.1 0.2 Fig 3: Channel spacing Vs Quality factor response at 187.5 THz, It can be seen that the quality of the signal decreases as the channel spacing decreases. 3
EYE CLOSURE (db) BER CROSSTALK (db) 10 0-5 -10 0-15 10-30 -20 0 10-50 -25 0 0.05 0.1 0.2 Fig 4: Channel spacing Vs BER response at 187.5 THz, It is observed that the value of bit error rate decreases as the channel spacing increases. The acceptable bit error rate values of 6.0 x, 9.59 x 10-14 and 3 x 10-57 are obtained at first channel at 0.05, 0.1 and 0.2 nm channel spacing respectively. 10-3 -30 0.05 0.1 0.2 Fig 6: Impact of channel spacing on the crosstalk for the designed DWDM system using Raman-EDFA HOA at 187.5 THz, After investigating the performance of the designed DWDM system using different channel spacings, it has been concluded that the value of crosstalk decreases as the channel spacing increases. It is found that by using 0.05 nm, 0.1 nm and 0.2 nm channel spacing, the value of crosstalk decreases by 0.89 db, 1.59 db and 2 db for the first channel, middle channel and last channel respectively. It is found that the designed DWDM system results in acceptable value of crosstalk. After this investigation, further some experiments have been done to check the response of DWDM at 0.1 nm channel spacing using different transmission distances and different input powers. a. Effect of change in Transmission Distance: 10-5 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Fig 5: Channel spacing Vs Eye Closure at 187.5 THz, A set up of 100 X 10 Gbps DWDM system using -20 dbm input power with a channel spacing of 0.1 nm using RAMAN-EDFA HOA, is designed. The 100 channels are transmitted using the frequency range of 187-190.975 THz. The comparison of performance of system having different transmission distances are noted in terms of BER, Quality factor, Eye Closure is shown below in figure 7, figure 8 & figure 9 respectively. The transmission distance considered here are from 80 km 200 km. Because below 80 km, the system is no more cost effective and above 200 km the system set up suffers from various non-linearities. So that s why transmission distance is taken from 80 km to 200 km. 4
EYE CLOSURE (db) BER BER QUALITY FACTOR (db) QUALITY FACTOR (db) 8 7 6 5 4 3 2 1 It has been observed that the quality of signal decreases and bit error rate increases as the transmission distance increases. b. Effect of change in input power: To investigate the performance of the system by using different input powers, -10 dbm, -5 dbm, 0 dbm, 5 dbm, 10 dbm, 15 dbm and 20 dbm input power values are taken. The comparison of the system performance is done in terms of BER, Q-factor, Eye Closure and crosstalk is shown below: 0 80 100 120 140 160 180 200 TRANSMISSION DISTANCE (Km) 8 7 Fig 7: Transmission Distance vs Quality factor at 187.5 THz, 10 0 6 5 4 3 2 1 0 10-12 10-14 80 100 120 140 160 180 200 TRANSMISSION DISTANCE (Km) Fig 10: Input Power vs Quality factor at 187.5 THz, Fig 8: Transmission Distance vs BER at 187.5 THz, 188.56 THz & 190.975 THz 10 0 10-1 10-3 10-5 10-12 10-7 10-14 10-9 80 100 120 140 160 180 200 TRANSMISSION DISTANCE (Km) Fig 11: Input Power vs BER at 187.5 THz, 188.56 THz & 190.975 THz Fig 9: Transmission Distance vs Eye Closure at 187.5 THz, 188.56 THz & 190.975 THz 5
EYE CLOSURE (db) CROSSTALK (db) -10 10-3 -15 10-5 -20 10-7 -25 10-9 -30-35 Fig 12: Input Power vs Eye Closure at 187.5 THz, Fig 13: Input Power vs Crosstalk at 187.5 THz III. CONCLUSION With this proposed set up of 100 X 10 Gbps DWDM system using RAMAN-EDFA HOA, The acceptable BER values of 6 X, 9.59 X 10-14 and 3 X 10-57 are obtained at the first channel (187.5 THz) at a channel spacing of 0.05 nm, 0.1 nm and 0.2 nm respectively. The maximum distance covered by using RAMAN-EDFA is 180 km at 0.1 nm channel spacing with BER value of 8.8 X 10-9, quality factor of 5.57 db & eye closure of 1.1 X db. Further it is found that at 0 dbm, the system performs well with BER values equal to 9.13 X 10-11, 1.67 X 10-12 & 1.64 X 10-7 at the first channel (187.5 THz), middle channel (188.56 THz) and at the last channel (190.975 THz) respectively. It is found that by using 0.05 nm, 0.1 nm and 0.2 nm channel spacings, the value of crosstalk decreases by 0.89 db, 1.59 db and 2 db for the first channel (187.5 THz), middle channel (188.56 THz) and the last channel (190.975 THz) respectively. REFERENCES [1] M.N. Islam, Raman Amplifiers for Telecommunications-2 Subsystems and Systems, Springer, pp. 430 431, 2004. [2] C. Jiang et al., Improved gain performance of high concentration Er3+ - Yb3+ - co doped phosphate fiber amplifier, IEEE J. Quantum Electron, Vol. 41, No. 5, pp. 704, 2005. [3] J.D. Downie, J.Hurley, S Ten, C.Towery, M.Sharma, Y. Mauro, C. Malouin, B. Zhang, J. Bennike, T. Schmidt and R. Sanders, DWDM 43 Gbps DPSK transmission over 1200 km with no inline dispersion compensation, Electronics Letters, vol. 46, no. 1, pp.60-62, 2010. [4] Simranjit Singh and R. S. Kaler, Flat-Gain L- Band Raman-EDFA Hybrid Optical Amplifier for Dense Wavelength Division Multiplexed System, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 25, NO. 3, 2013. [5] Shien-Kuei- Liaw, Yi-Lin-Yu and Ren-Young Liu, Hybrid Optical Amplifiers: Design and Investigation, IEEE, 978-1-4799-3282, 2014. [6] J.-X-Cai, H.G. Batshon and D.G. Soursa, 49.3 Tb/s Transmission Over 9,100 km Using C+L EDFA and 54 Tb/s Transmission Over 9,150 km Using Hybrid Raman-EDFA, Journal of Lightwave Technology- 17351, 2015. [7] Pardeep Kaur and Daljeet Singh, Performance Analysis of HOA in PI-DPSK DWDM System at Ultra Narrow Channel Spacings, IJEEE, Volume 2, Issue 3, June 2015. [8] Benyuan Zhu, J.Zhang, Jianjun Yu, David W. Pechham, Robert Lingle, Man F. Yan, P.Wisk and David Di Giovanni, 34.6 Tbps Single Band Transmission over 2400 km Fiber using Complimentary Raman/EDFA, OFC, 2016. 6