IMPROVING LINK PERFORMANCE BY ANALYSIS OF NONLINEAR EFFECTS IN FIBER OPTICS COMMUNICATION Hirenkumar A. Tailor 1, Antrix Chaudhari 2, Nita D. Mehta 3 Assistant Professor, EC Dept., S.N.P.I.T & R.C, Umrakh, Bardoli, Gujarat, India 1 PG. Student, EC Dept., Dr. S & S S Ghandhy Govt. Engg. College, Surat, Gujarat, India 2 Asso. Prof., EC Dept., Dr.S & S S Ghandhy Govt. Engg. College, Surat, Gujarat, India 3 Abstract: In order to expand the capacity of optical fiber communication system the most important phenomena is the emergence of wavelength division multiplexing (WDM). Using WDM, multiple channel of information can be transmitted on single fiber. There are some limiting factors related to data rate and capacity in WDM optical fiber communication system. These limiting factors can be linear or non-linear. The most important non-linear effect occur in the fiber optics communication system are Self phase modulation (SPM), Cross phase modulation (XPM) and Four wave mixing ( FWM). Self phase modulation (SPM) occurs only in single channel fiber optics communication system and Cross phase modulation (XPM), Four wave mixing (FWM) have impact on multichannel WDM fiber communication system. In this paper, we analyze the impact of Self phase modulation (SPM), cross phase modulation (XPM) on WDM communication system for different parameters. We also describe some novel technique to reduce the effect of these nonlinearities (SPM, XPM) in WDM fiber communication system. Keywords: Cross phase modulation (XPM), Four wave mixing (FWM), Optical fiber communication, Self phase modulation (SPM). I. INTRODUCTION The terms linear and nonlinear in optics mean intensity independent and intensity dependent phenomenon respectively. As long as optical power within the fiber is small, fiber can be treated as a linear medium that is loss and refractive index are independent of signal power [1]. But when power level in the system increases nonlinear effect comes into picture. Nonlinearity effects arose as optical fiber data rates, transmission lengths and optical power level increases [2]. Nonlinear effects in optical fiber occur due to change in the refractive index of the medium with optical intensity. The power dependence of refractive index is responsible for the kerr effect [1]. There are three types of fiber nonlinearities due to the Kerr effect namely (i) Self phase modulation (SPM) (ii) Cross phase modulation (XPM) (iii) Four wave mixing (FWM). All rights reserved by www.ijaresm.net ISSN : 2394-1766 1
In this paper, SPM and XPM with and without Fiber Bragg Grating (FBG) [5] and Dispersion Compensation Fiber (DCF) techniques were studied using Optisystem software. A. Self phase Modulation (SPM) SPM is a phenomenon that is due to the power dependency of the refractive index of the fiber core. Time varying signal intensity produces a time varying refractive index. The higher intensity portions of an optical pulse encounter a higher refractive index of the fiber. The leading edge will experience a positive refractive index gradient (dn/dt) and trailing edge a negative refractive index gradient ( dn/dt) [1]. This temporally varying index change results in a temporally varying phase change, this nonlinear phase modulation is self-induced so it is called as self-phase modulation. B. Cross phase Modulation(XPM) Cross phase modulation is SPM except that it involves two or more pulses of light. Two pulses each travel down the fiber changing the refractive index as the optical power varies. If two pulses happen to overlap they will introduce distortion into the other pulses through XPM. This distortion occurs because the nonlinear refractive index seen by an optical beam is depends on both, the intensity of that beam as well as co propagating beam [2]. II. SIMULATION OF SELF PHASE MODULATION Simulation have been carried out to illustrate the performance of self phase modulation. Simulation blocks divide into three parts: transmitter, fiber channel and receiver. Figure 1: Design of SPM The transmitter block contains pseudo Random data generator, Non Return to Zero (NRZ) modulator, continuous wave laser, Mach-Zehnder amplitude modulator and EDFA amplifier component blocks. The CW laser block is used to generate the optical light signal wave. The NRZ rectangular pulses and CW laser output is sent to amplitude Mach-zehnder modulator, which is an electro-optical modulator used to modulate the light wave with respect to transmitted electrical signal and generates an optical signal at the output of modulator. Fiber channel in the figure1 is shown as an iterative loop component. The iterative loop component consists of fiber, fiber compensating technique component and In-line optical amplifier. The input optical signal is sent over the fiber. Output of the fiber is then sent to an Inline optical amplifier to amplify signal. Output of the amplifier is sent to fiber grating, which is used to compensate the distortion of signal by inducing dispersion after each stage. Fibers grating compensator is used to reflect particular wavelengths of light and transmits others, achieved by varying refractive index (varying intensity of light). All rights reserved by www.ijaresm.net ISSN : 2394-1766 2
The main blocks of the receiver system are photodiode, a Bessel filter, BER analyser and an electrical oscilloscope. The filter is used for pulse shaping to minimize intersymbol interference. Filter configuration is set to low pass filter. Output of photodiode is sent to Bessel's filter. Electrical scope is used to capture the output electrical signal. For the visualization of BER, Q factor & eye diagram BER analyzer is used. Using simulation different parameters like Fiber length, Data rates and Input power were studied. In simulation setup 30 km fiber length was considered and results are illustrated for without FBG (Fiber Bragg Grating) in figure 2 and using FBG in figure 3. Also, simulation results were studied for 10 Gbps data rates and results are shown in figure 4 for without FBG and for using FBG in figure 5. Furthermore, simulation results were taken for 25 dbm input power and results are depicted in figure 6 for without FBG and for using FBG in figure 7. All rights reserved by www.ijaresm.net ISSN : 2394-1766 3
Comparison of Q factor & BER for different parameters like Fiber length, data rates and input power are presented in Table 1, Table 2 and Table 3 respectively. parameter Values Q factor BER Q factor BER 20 km 52.049 0 78.37 0 Fiber 22 km 37.71 1.347e-311 54.97 0 Length 24 km 21.69 8.464e-105 55.55 0 26 km 17.56 1.723e-069 39.32 0 28 km 15.32 1.986e-053 35.34 3.009e-274 30 km 15.03 1.412e-051 31.53 9.847e-219 Table 1 Comparison of Q factor & BER for fiber length parameter parameter Values Q factor BER Q factor BER 7 Gbps 3.38 0.00031 40.28 0 Data Rates 8 Gbps 3.00 0.00131 39.00 0 9 Gbps 3.39 0.00039 37.00 4.451e-300 10 Gbps 3.32 0.00044 34.20 6.911e-277 Table 2 Comparison of Q factor & BER for data rates parameter parameter Values Q factor BER Q factor BER Input 15 dbm 103..68 0 144.49 0 Power 17 dbm 111.69 0 184.67 0 20 dbm 45.78 0 104.99 0 22 dbm 41.35 0 96.87 0 25 dbm 17.14 3.279e-66 26.83 4.465e-159 Table 3 Comparison of Q factor & BER for input power parameter All rights reserved by www.ijaresm.net ISSN : 2394-1766 4
III. SIMULATION OF CROSS PHASE MODULATION Simulated block diagram of XPM using FBG is shown in figure 8. Figure 8: Design of XPM using FBG In XPM two parameters Input power and Number of input channels were analysed with and without FBG and DCF. Figure 9 shows the output results for 12 dbm pump power without FBG and DCF. Figure 10 illustrate the output results for 12 dbm input power using DCF and figure 11 shows the results for 12 dbm pump power using FBG. Figure 11: 12 dbm pump power using FBG Furthermore, simulation results for 11 input channels without FBG is depicted in figure 12 and results for 11 input channels using FBG is depicted in figure 13. All rights reserved by www.ijaresm.net ISSN : 2394-1766 5
Paramete r Pump power Without any compensation Technique With DCF Values Q factor BER Q factor BER Q factor BER -7 dbm 3.89 4.242e-005 7.727 4.557e- 8.74 8.528e- 015 019-5 dbm 3.85 5.055e-005 7.70 5.623e- 8.79 5.839e- 015 019-2 dbm 3.78 6.606e-005 7.58 1.420e- 8.75 8.289e- 014 019 0 dbm 3.73 8.083e-005 7.44 4.170e- 8.65 2.033e- 014 018 2 dbm 3.66 0.00014 7.23 1.996e- 8.46 9.975e- 013 018 5 dbm 3.52 0.00018 6.72 7.184e- 7.97 5.781e- 012 016 8 dbm 3.28 0.00043 5.88 1.594e- 7.13 3.660e- 009 013 12 dbm 2.73 0.0027 4.17 1.198e- 5.38 2.770e- 005 008 Table 4: Comparison of Q factor & BER for pump power parameter parameter values Q factor BER Q factor BER 11 channels 3.38 0.00032 5.11 1.436e-007 Number of 18 channels 3.47 0.000236 5.27 5.995e-008 channels 26 channels 2.77 0.00247 4.30 7.535e-006 Table 5: Comparison of Q factor & BER for number of channels parameter IV. CONCLUSION The behavior of SPM versus the optical power, fiber length & bit rate has been investigated. By increasing power, SPM grows and deplete the signal. By increasing Fiber length & bit rate we got poor BER performance & worse Q factor at the receiver. With the use of FBG compensation Technique we can easily overcome SPM effect. The nonlinearity i.e. XPM increase in optical fiber communication system by increasing the input power and number of channels. Furthermore, two techniques for compensating the XPM effect have been adopted. i.e. Dispersion Compensating Fiber (DCF) & Fiber Bragg Grating (FBG). Simulation Result shows that Fiber Bragg Grating is better compensation technique than DCF. All rights reserved by www.ijaresm.net ISSN : 2394-1766 6
REFERENCES [01] S.P Singh and N. Singh, Nonlinear effects in optical fibers: Origin, Management and applications", progress in electromagnetic research, PIER 73, 249-275, India, 2007. [02] Kapil Kashyap, Dr. Hardeep Singh, Preeti Singh, Chetan Gupta Effect of Cross Phase Modulation (XPM) on Optical Fiber Using Two Wavelength Division Multiplexed (WDM) Channels IJETCAS 13-197; Volume 5, Issue 4, pp 536-540, 2013. [03] Mayank Srivastava and Vinod Kapoor Analysis and Compensation of Self Phase Modulation in Wavelength Division Multiplexing System IEEE Students Conference on Engineering and Systems 978-1-4799-4939-7/14 2014. [04] Ibrahim A. Murdas, Talib M. Abbas, Zainab A. Abbas Numerical Simulation for Self Phase Modulation and Cross Phase Modulation in Optical Fiber International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Volume 3 Issue 11 November 2014. [05] Nordiana Mohamad Saaid Nonlinear Optical Effects Suppression Methods in WDM Systems with EDFAs: A review IEEE International Conference on Computer and Communication Engineering, 978-1-4244-6233-9/10 2010. All rights reserved by www.ijaresm.net ISSN : 2394-1766 7