High Performance Soliton WDM Optical Communication System

Maninder Singh Electronics and Communication Engineering,

Indo Global College of Engineering, Mohali 140109, Punjab-India, Email ID:md_singh1989@yahoo.com

Hardeep Singh Saini Electronics and Communication Engineering,

Indo Global College of Engineering, Mohali 140109, Punjab-India, Email ID:hardeep_saini17@yahoo.co.in

Abstract-- The use of Soliton pulse falls in an area of emerging engineering and technology promising great changes in the functionality and capacity of optical data transmission and networking. In this paper, the main objective is to familiarize with the basic analytical propagation model of the soliton pulse in Wavelength Division Multiplexing (WDM) system. For this proposed model, we used a soliton pulse, which will be carried out at the transmitter and receiver end easily. The soliton pulse propagations are basically based on the numerical solution of Non-linear Schrödinger Equation [NLSE], and also in some special case it is problem to solve it analytically. We have studied a propagation of soliton pulses in WDM system using a simulation tool Optisim. The main parameter, on which we have concentrated in our present work are BER, Jitter, Q-factor and power drop.

Keywords: Optical Communication, Solitons, WDM, Bit Error Rate, Q-factor;

I. INTRODUCTION The soliton word means ''Solitary Solution'' and

suggests particle like behavior or properties of pulse which is in propagation in a non-linear medium [1]. The soliton is a self-reinforcing solitary wave (a wave packet or pulse) that keeps its shape while traveling at constant speed. Soliton pulse arises as the solution of a widespread class of the weakly non- linear disperse particle differential equation describing physical system. The properties of soliton are:-

1. They are of permanent form. 2. They are localized with in a region. 3. They can interact with solitons and

emerge from the collisionunchanged except for a phase shift.

The main advantages of the solitons used in the fiber optics telecommunication system are that it does not change a pulse shape during propagation from transmitter to receiver section. The soliton phenomenon was first introduced by John ScottRussell, a Scottish engineer at Edinburgh (1834) who observed solitary wave in the union canal in Scotland. After that he reproduced the phenomenon in wave tank and named it the “wave of translation” [2].

In 1872 Boussinesq’s equation and in 1895 KortewegdeVries (KDV) equation proved that these solitary pulse were indeed possible theoretically. After about 70 years, in 1965, word soliton was first used in research paper by Zabusky and Kruskal, in which they solved the KDV equation by boundary equation. In 1967, Gardner et al found an exact solution of the KDV equations which is called inverse scattering transform [3].

Solitons are solution to nonlinear differential

equation e.g.:- 1. KDV equation, describes wave on

shallow water. 2. Non –linear Schrodinger equation (optics

and water waves).

In optics, the terms solitons refer to any optical field in which it does not change shape during propagation due to balance between non-linear& linear effect in the medium [4] or we can say balance between the Group Velocity Dispersion (GVD) and Self-phases Modulation (SPM) [5].There are basically two types of solitons: one is spatial soliton, in which non-linear effect can balance the diffraction. In this, electromagnetic field can change the refractive index of the medium during propagation of pulses, thus creating a structure which is similar to a graded -index fiber. Second is temporal solitons, in this if electromagnetic field is already spatially confined, then it is possible to send pulse which will not change their shape because of the non-linear effect. So it is simplified as “soliton” in optics [4].

The performance of communication system depends upon some parameters i.e. Bit Error Rate (BER), Jitter and Q-Factor etc. BER is defined as number of errors made per second. In other words the reliability of the communication system form bit in to bit out. Lesser the value of BER means good transmission or fewer errors in received signal. The bit error rate improves as Q-factor increases. Another important factor which also plays a very important role for efficient communication system is Jitter.The transmission of high speed signals causes impairments at various stages leading to timing errors. Jitter is one such timing error resulting from the misalignment of rise and fall time. Hence to improve the performance

2014 Fourth International Conference on Advances in Computing and Communications

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DOI 10.1109/ICACC.2014.11

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of communication system the Q-factor should be high, Jitter and bit error rate should be low as possible.

In this paper, we used Wavelength Division Multiplexing (WDM) system which is backbone of all optical networks, because of demand of high capacity for the data transmission. In this, multiple optical signals can be easily transmitted over a single optical fiber. In WDM system each communication channel have different wavelength and which are multiplexed by multiplexer onto a single fiber and vice versa, de-multiplexer is used at the receiver section which separates the different wavelength [6].

II. PROPAGATION OF SOLITON PULSE IN OPTICAL FIBER

The major element in the transmitter section is a Return to Zero (RZ) pulse generator. A simple approach to generate RZ pulses is to employ an optical modulator and a Non-return to Zero (NRZ)-to-RZ converter, driven by a Distributed Feedback Laser (DFB) source. In this case, a Mach–Zehnder modulator is used to modulate the NRZ data at the desired transmission rate Instead of using a single NRZ data stream; however, it is useful to modulate an optical NRZ signal incorporating several multiplexed NRZ data streams before the conversion into RZ pulses takes place.At the receiving end the incoming signal requires conversion back from RZ to NRZ and then finally a de-multiplexer separates the specific NRZ data for each channel as shown in Figure1.

We have studied the soliton pulse propagation mathematically by the Non-linear Schrodinger (NLS) equations. A(x,y) is along propagation axis ‘x’ & on time ‘y’ dependent amplitude of the mode[7].

����� ���

������ ��

� � ����� ����� (1)

By using this method, we also studied the impact

of Self-phase modulation (SPM) & Cross-phase Modulation (XPM) using a numerical approach. In “Equation (1)” we neglected the 3rd order dispersion and also added the term which contains fiber losses and includes periodic amplification of the signal by treating it as a function of X. The parameter�� is the effect of dispersion of the second order.

�

���

(2) Where Vg is group velocity associated with the

pulses (GVD).The non-linear parameter � which depend inversely on the effective core area, so the fiber non-linear ties can be reduced by on enlarging

����

and

� ��� �����

Above equation represents the dimensionless combination of the pulse and fiber parameter. When��� >0, the solution exhibits a dip in a constant intensity background and such solitons are known as bright solutions [5, 8].

III. SIMULATED MODEL AND RESULT The “Equation (1)” can be normalized in the form �=0 and �=0

� �������������

�� �������! �

"#� (3)

Where $% its pulse width, &' is peak power of pulse and

() $'

*� *

L D is dispersion length, then“Equation (1)”becomes

��� �+�, - ��+���� & �!� ! . (4)

Where;

/ 01�2� 3 45�67 , 5

which depends on whether � is positive or negative. The parameter P is defined as:

����& �&%�() �#����

*��* (5)

Where () = dispersion length, &%�= Peak power of pulse, $%=pulse width. Above equation can be solved by the inverse scattering [9 - 12].

8.� �9 &�/:;<8�9 (6)

During propagation of input pulse having an initial amplitude is launched into the fiber, its shape not changed when P=1. The =% basically defined as the distance over which higher – order solition recover their original shaped and it is given by “Equation (7)”.

=% � ()

� �>�

*��* (7)

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The soliton period =% and solition order P, both is playing importance in the optical soliton [5]. We have studied propagation of solitons pulses in the WDM system using a simulation tool Optisim which is shown in the Figure 2. In this we have taken four signals NRZ modulated at the 3.48 GB/s rate, transmitted over a medium long haul link with 1 nm spacing (Figure 2). NRZ format is basically used in solitons because the signal bandwidth is about 50% smaller than RZ format. But as information bits, NRZ cannot used in solitons because the pulse width must be small fraction of the bit slot to ensure that the neighboring soliton are well separated.

� ��? � @>�>

(8)

Where TB duration of bits slot is �A% �?�>

is separation between neighboring solitons [5]. The entire four channel have difference central frequency like channel 1 have center frequency equal to center frequency -1.5*channel spacing. Then all the outputs of the channel go in multiplexer and through them it is transmitted over channel L=50km in single mode fiber and the de-multiplexer separates the signal at the receiver section. To authenticate the results we have also simulated CW transmitter and compared the results of the received signals in both the communications system. The Figure 3 shows the CW pulse transmitter and Figure 4 shows the soliton pulse transmitter used in the WDM optical system. One of the four channels of WDM system is detected and their spectra, eye-diagram and Q- value are evaluated. The various parameters i.e. noise, inter-symbol interference, jitter, if the signals are too long or too short, poorly synchronized with the system clock, or have too much undershoot or overshoot, can be observed from the eye diagram. In other words, we can say that system performance can be measured from eye diagram. The results of the simulated model in case of propagation of CW pulse (Figure 6) are 9.45db Q-factor, bit error rate (BER) about 0.0015 and jitter 0.0920. Similarly in case of solitons wave system, one of the four channels of WDM system i.e. receiver 3 channel is evaluated as shown in Figure 5, and results are: Q factor is 10.77 db, BER is 0.0003 and jitter is 0.0834. Another important parameter that was analyzed is “drop in power”. We analyzed I/P and O/P power at point of “Total I/P” in transmitter section & at “Total O/P” in receiver section, as illustrated in Figure 2, respectively for both type of communication system. The highest peak frequency of I/P and O/P signal is fixed at 193.4777 THz, in both systems.

The observations are as under:

• In case of CW pulse system, the highest peak power of I/P signal is 20.097862 dB [mw/THz] and highest peak power of O/P is 10.300847 dB [mw/THz] as shown in Figure7 and Figure8 respectively.

• In case of soliton based WDM system, Figure 9 and Figure10 shows the highest peak power of I/P signal is 30.24052 dB[mw/THz] and highest peak power of O/P is 21.849026 dB[mw/THz] respectively.

The performance of the soliton based WDM system is better as compared to CW pulse system, because the drop in power in former is 9.797015 dB [mw/THz] and in later system it is 8.425026 dB [mw/THz].The performance of WDM solitons based optical system gives better results as compared to CW pulse WDM communication system. The performance of communication system improved due to high Q factor, low Jitter, bit error rate and low drop in power of the signal. In all concepts solitons approach made transmission systems intrinsically stable.

IV. CONCLUSION The “soliton philosophy” controls, balances and even extracts the maximum benefits of the fiber dispersion and non-linearity which otherwise are of detrimental effects. We had simulated a WDM based optical communication system for the propagation of CW pulses and solitons waves. In both cases we transmitted four signals by multiplexing and at the receiver side after de-multiplexing, examined the parameters of one signals out of four. We conclude that the performance of WDM solitons based optical system gives better results. The solitons approach made transmission systems intrinsically stable. The performance of communication system improved due to high Q factor, low Jitter, bit error rate and lesser drop in power of the signal. REFERENCES

[1] N. Zabusky,M.D. Kruskal, Interaction of Solitons in a

Collision-Less Plasma and the Recurrence of Initial States, Physical Review Letters1965,15(6), p.240;

[2] Wikipedia http://en.wikipedia.org/wiki/ Soliton_(optics)

[3] L.F. Mullenauer, R.H. Stolen and J.P. Gordon, Physical Review Letters1980, 45, p. 1095.

[4] Wikipedia http://en.wikipedia.org/ wiki/ Soliton [5] G.P. Agrawal, Fiber Optics Communication System,

Third Edition, by John Wiley & Sons, New York, 2002.

[6] J. Gurjal and M.Singh, Performance Analysis of 4-Channel WDM System with and without EDFA, IJECT2013, 4(Spl-3), p. 70;

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[7] G.P. Agrawal, Applications on NoOptics, ISBN: 0-12-045144-1, 3rd editAcademic Press, CA, 2001.

[8] L. Bohac, The SolitonTransmission inInformation and Communication TeServices (IEEE)2010, 8(5), p.107;

[9] G.L. Lamb, Elements of Soliton TheNew York, 1994.

[10] T. Miwa, Mathematics of SolutioUniversity Press, New York, 1999.

Figure 1. B

Fig

Figure 3. CW Pulse Transmitter

on-Linear Fiber tion, San Diego:

nOptical Fibers, echnologies and

eory, by Wiley,

ons, Cambridge

[11] V.E. Zakharov, A.B.Shabat, EDimensional Self-Focusing aSelf-Modulation of Waves in NEksp. Teor. Fiz. 61(1971) p.11Phys. JETP 34, 1972, p.62;

[12] M.J. Ablowitz, P.A.Clarkson, Evolution Equation and InvLondon Mathematical Society 149, Cambridge University Press

lock Schematic of an Optical Fiber Communication System

gure 2. WDM Transmission and Receiving System

r Figure 4.Soliton Trans

Exact Theory of Two-and One-Dimensional Non-Linear Media, Zh. 18; English transl.Sov.

Solutions Non-linear verse Scattering1999,

Lecture Note Series s, New York.

smitter

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Figure 5. Eye Diagram at Receiver end in SolitSystem

Figure 6.Eye Diagram at Receiver end in CW Pu

System

Figure 7. Input Optical Spectrum in CW Pulse

on based Optical

ulse based Optical

e at Transmitter

Figure 8. Output Optical Spectrum in

Figure 9. Input Optical Spectrum in Soli

Figure 10. Output Optical SpectrumTransmitter

CW Pulse at Receiver

iton Wave at Transmitter

m in Soliton Wave at

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