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ISSN : 2230-7109 (Online) | ISSN : 2230-9543 (Print) IJECT Vol. 5, Issue 4, Oct - Dec 2014 Analysis and Compensation of Four Wave Mixing Products in Wavelength Division Multiplexing System 1 Himakshi Sharma, 2Er. Gian Thakur P.G. Scholar, Dept. of ECE, L.R.I.E.T Solan (H.P), India Asst. Professor, Dept. of ECE, L.R.I.E.T Solan (H.P.), India 1 2 Abstract In this paper we had investigated the non-linearity i.e. Four Wave Mixing in Wavelength Division Multiplexing system. Also the effect of phase mismatching (dispersion) and Optical signal to noise ratio is analyzed. The effect of channel spacing and increasing number of channels is taken into account. This works aims at finding the new possibilities to mitigate the effect of four wave mixing in Wavelength Division Multiplexing systems. The outputs are analyzed in optical spectrum analyzers. where N is the number of wavelengths to transmit such a high capacity over long distance requires operation in the 1550-nm window of dispersion shifted fiber. In order to preserve an adequate signal to noise ratio, a 10 Gbps system operating over a long distance and having minimal optical repeater spacing of 100 km needs optical power launch of around 1mW per channel. For such WDM system, the simulation requirements of high launch power and low dispersion give rise to the generation of new frequency due to four wave mixing [8]. Keywords Four Wave Mixing (FWM), Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS), Bit Error Rate (BER), Optical Spectrum Analyzer (OSA), Optisystem, Wavelength Division Multiplexing (WDM). III. Experimental Setup The simulation arrangement for FWM configuration is shown in fig. 1. Block diagram of the system is divided into three sections: transmitter, channel and receiver. In transmitter section first block is data source where data rate and bit is customized. The data source is the pseudo number sequence. Electrical driver is used to convert binary sequence into electrical pulses; continuous wave lorentzian laser is used with various values of power. Booster can also be used which is an EDFA with fixed output power and further fixed gain optical amplifiers are used. Channel section basically consists of optical fiber and band pass Bessel electrical filter. In receiver section an optical spectrum analyzer is used to access the non-linear output of optical spectrum along with that a power meter is used to view the power ratings in receiver side. I. Introduction This article provides concepts of Four Wave Mixing which is a type of Nonlinearity. Due to the widespread growth in wireless communication, network operators are facing difficulty in accommodating the growing traffic. WDM appears to be a viable solution to such problems posed by the micro cellular system [1]. WDM system however suffers from nonlinear effect in fiber [2]. Communications in WDM generate new waves under appropriate condition through a variety of Non-linear phenomena such as Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS), Self-Phase Modulation (SPM), and Four Wave Mixing (FWM). Four wave mixing or four photon mixing is the process whereby optical power in one channel in the WDM system is spilled over into an adjacent channel [3]. Such powers transfers not only results in the power loss for the channel but also induces inter channel crosstalk that degrades the system performance severely. FWM is also useful in designing light wave systems. It is often used for demultiplexing channels when time-division multiplexing is used in the optical domain [4]. It can also be used for wavelength conversion. Wavelength conversion is a significant function in the future broadband multichannel light wave system because it makes many other possible useful functions such as wavelength reuse and dynamic wavelength routing and switching [5]. FWM in optical fibers is occasionally used for generating a spectrally inverted signal through the process of optical phase conjugation. II. Four Wave Mixing Four wave mixing also termed as four photon mixing is one of the most governing signal degradation effect in the WDM system. Four wave mixing is the third order non-linearity in the in silica fiber that is analogous to intermodulation distortion [6]. It mostly occurs with the dense channel spacing and low chromatic dispersion. Channels in the WDM system are equally spaced which tends to the generation of new waves which will fall at channel frequency by FWM, and thus give rise to crosstalk [7]. Dense WDM transmission in which individual wavelength channel are modulated at the rates of 10Gbps offer volumes of N*10 Gbps, 134 International Journal of Electronics & Communication Technology Fig. 1: Experimental setup of FWM IV. Results and Discussion Two WDM channels were launched over a single optical fiber of span 10Km. Dispersion was completely compensated at each channel. The fiber dispersion value was varied from -6 (ps/nm/ km) to 14 (ps/nm/km) through individual runs. The optical power spectrum of the received signal shows that the FWM product decreased with increasing dispersion. Also negative dispersions were used which could be easily compensated locally. The OSNR seemed to show high rate at using negative dispersion. Fig. 2(a) and fig. 2(b) had shown the optical signal spectrum at the transmitter end and receiver end at zero dispersion values. By matching them we had found that at receiver end two extra peaks had appeared which nothing but the noise was in the system due to FWM phenomena. There are certain parameters which need to be preset: 1. Attenuation =0 2. Effective area = 53µm2 3. Input power =1mW 4. Degeneracy =6 5. Fiber length =10km w w w. i j e c t. o r g IJECT Vol. 5, Issue 4, Oct - Dec 2014 ISSN : 2230-7109 (Online) | ISSN : 2230-9543 (Print) Table 1: Dispersion vs. OSNR Dispersion (ps/nm/km) -5 -4 0 4 8 14 Received signal power(dbm) -45.950 -46.088 -45.956 -45.951 -45.949 -46.983 OSNR 47.86 47.84 47.58 47.02 46.97 46.07 or decreasing value beyond “0” actually increases phase mismatch which help in vanishing extra peaks. Fig. 2(d and e) showed outputs at “4” and “-5” values. Outputs were also calculated for each of the values showed in Table 1. Fig. 2(c): Output of Optical Spectrum Analyzer at “0” dispersion. Fig. 2(a): Output of Optical Spectrum Analyzer at transmitter end. Fig. 2(d): Output of Optical Spectrum Analyzer at “4” dispersion Fig. 2(b): Output of Optical Spectrum Analyzer at receiver end at “-5”dispersion. Fig. 2(b) showed the Dual OSA output at dispersion value -5 (ps/nm/km). Clearly it could be seen from table 1.That we got best result at “-5” value with highest OSNR which was required. Similarly fig. 2(c) showed result at “0” dispersion value that has maximum noise and that was due to phase matching. By increasing w w w. i j e c t. o r g Fig. 2(e): Output of Optical Spectrum Analyzer at “-5” dispersion International Journal of Electronics & Communication Technology 135 IJECT Vol. 5, Issue 4, Oct - Dec 2014 Fig. 2(f): Plot between OSNR vs. Dispersion. ISSN : 2230-7109 (Online) | ISSN : 2230-9543 (Print) Himakshi Sharma received her B. Tech. degree in Electronics and Comm. from Himachal Pradesh University (HPU), Shimla, India, in 2012, the M. Tech. degree in Electronics and Communication Engineering from Himachal Pradesh Technical University (HPTU), Hamirpur, India, in 2014. Her research interests include digital signal processing, electronic measurement techniques,antenna and optical technique and networks. At present, she is engaged in research in optical fiber nonlinearities. Fig. 2(f) showed the comparison graph between proposed and existing scheme. And the OSNR came out to be high which was required. V. Conclusion For the given experimental set up various values of dispersion had been changed accordingly. The results given in fig 2(a, b, c, d and e) had been showing the plot between optical power and dispersion values. Here the spectrum of the received signal had shown that FWM product decreased with increasing dispersion or more exactly the best value of OSNR came out t “-5” dispersion. Thus in conclusion it had been illustrated that FWM products in WDM system was stronger at lower fiber dispersion values. However at zero dispersion value due to phase-matching condition the FWM effect came out to be extreme. By increasing the fiber dispersion the phase mismatch increased and FWM effect decreased. References [1] Naresh Kumar, Ajay K. Sharma, Vinod Kapoor,“XPMInduced Crosstalk with Variety of Fiber in SCM-WDM Optical Transmission Link”, pp. 2125-2127. [2] Naresh Kumar, Ajay K. Sharma, Vinod Kapoor, “Improved XPM-Induced Crosstalk with Higher Order Dispersion in SCM-WDM Optical Transmission Link”, pp. 941-944. [3] Govind P. Agrawal,“Fiber-Optic Communication System”, 3rd ed., Wiley, New York, 2002. [4] Govind P. Agrawal,“Nonlinear Fiber Optics”, Third Edition. [5] Gerd Keiser,“Optical Fiber Communications”, McGraw-Hill, fourth edition. [6] C. Siva Ram Murthy, Mohan Gurusamy,“WDM Optical Networks Concepts, Design, and Algorithms”, Prentice-Hall India. [7] S. Pachnicke, E De Man, S. Spalter, E. Voges,“Impact of the Inline Dispersion-Compensation Map On FWM - Impaired Optical Networks”, IEEE Photonic Technology Letters, Vol. 17, No. 1 January 2005. [8] Jian Hui Zhou, Namkyoo,“Four Wave Mixing Wavelength Conversion Efficiency in semiconductor Travelling wave Amplifiers Measured to 65nm of Wavelength shift”, IEEE Photonics Technology Letter, Vol. 6, No. 8, August 1994. [9] T. Sabapathi, S. Sundaravadivelu,"Analysis of Bottlenecks in DWDM Fiber Optic Communication System”, Optik 122, pp. 1453– 1457, 2011. 136 International Journal of Electronics & Communication Technology w w w. i j e c t. o r g