performance analysis of spm and fwm nonlinear effects on...

38 Manju, Surajmukhi, Kuldeep Singh

International Journal of Engineering Technology Science and Research

IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 6

June 2017

Performance Analysis of SPM and FWM Nonlinear Effects on

WDM Link

Manju*, Surajmukhi**, Kuldeep Singh***

*(Department of Electronics and Communication Engineering, Guru Jambheshwar University of Science and

technology, Hisar

** (Department of Electronics and Communication Engineering, Guru Jambheshwar University of Science

and technology, Hisar

*** (Assistant. Professor, Department of Electronics and Communication Engineering, Guru Jambheshwar

University of Science and technology, Hisar

ABSTRACT

In this paper, the optical communication link at 10 Gbps per channel using NRZ modulation has been simulated with 0.2

nm channel spacing. The performance of 4-channel WDM link under the effects of Self-Phase Modulation (SPM) and

Four Wave Mixing (FWM) has been exercised. The simulated results show that the fiber link with a distance of

approximately 120 km at transmitted power of 10 mW may be designed with value of Q factor and BER is quite above the

threshold level. The performance of four channels on WDM has been evaluated in terms of Q-factor, BER against

various factors like power, dispersion and length to study the nonlinear effects. The main reason of nonlinear effects are

change in inelastic scattering and refractive index of the fiber. These nonlinear effects degrades the transmission of light

signal in Wavelength Division Multiplexing (WDM) system. So these nonlinear effects are necessary to study. The factors

which are responsible for these effects are analyzed using OPTSIM simulation tool.

Keywords - BER, FWM, SPM, Q-factor, XPM

1 INTRODUCTION

These days fiber optical technology is used for

better data transmission rates, wide bandwidth,

insusceptibility to interference, electrical

inaccessibility, signal safety with minimum losses

etc. But during this transmission some nonlinear

effects are visible at high power levels which

affects the high data rates. So, different types of

schemes can be used to increasing capacity, quality

and mitigate these nonlinear effects occurs in

optical fiber technology. But some physical

limitations occurs in the optical fiber these limiting

factors are linear or nonlinear. These linear and

nonlinear effects are intensity dependent or

independent. The nonlinear effects are occurs at

high power levels and affects the system

performance. When the power level increases above

10 mW different type of nonlinearity comes.

Nonlinear effects are categorized in to two types

called inelastic scattering effects and refractive

index effects. Due to refractive index SPM (Self-

phase modulation), FWM (Four wave mixing) and

XPM (Cross phase modulation). Owing to inelastic

scattering SRS (Stimulated Raman Scattering) and

SBS (Stimulated Brillion Scattering). The main

difference between those are that SRS taking place

in both directions forward as well backward and

gives incoherent optical wave. But SBS is in the

forward direction only gives coherent acoustic wave

[1].

1.1 Self-Phase Modulation

In Self-phase modulation phase shift of a

propagated optical signal is self-induced so it is

called self-phase modulation [2]. When the optical

signal of high intensity is transmitted through the

fiber the refractive index of material gets modified

because of this modification in the phase of

propagated signal taking place. The refractive index

of fiber is to be governed by the intensity of the

optical wave. The temporarily change in refractive



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 6

June 2017

index causes phase shift to fluctuate with time in the

optical field phase changes by [2] which can be

represented as:

Where n belongs to linear refractive index

belongs to nonlinear refractive index of the

fiber. defines the intensity of the optical signal

and is called as free space wave number given

by =2 / denotes the wavelength of optical

signal. L defines the length of the optical fiber. The

frequency shift in the optical signal occurs due to

the nonlinear phase shift and this frequency shift is

called frequency chirping. The new frequencies are

generated by the self-phase modulation due to this

pulse broadening taking place at the output

spectrum and this increases the signal bandwidth

which affects the performance of optical fiber

communication systems [1]. Self-phase modulation

(SPM) is a type of nonlinear effect, which arises in

WDM systems when optical signal is launched into

a fiber.

Sequence

generator

Electrical

pulse

generator

ge

Optical

source

Optical

Modulator Analyser Optical

receiver

Optical

fibre

Figure 1 ‘‘block diagram of self-phase modulation’’

1.2 Four Wave Mixing

When we transmitted three waves of

frequencies , and fourth wave is

generated by these three waves of

frequency so it is called four

waves mixing [3]. Four waves mixing is the

nonlinear effect of a material to an applied optical

field. Due to this polarization effect induced in the

fiber consists of not only linear terms but also

nonlinear terms. This process is generated by third

order nonlinear Susceptibility. This FWM effect

does not depends on the bit rate but depends on the

channel spacing and fiber dispersion.in general, if N

waves are transmitted into the fiber, the no of FWM

generated mixed products M is given by [4]

M= (N-1)/2

These SPM nonlinear effects degrades the

performance of the optical fiber communication and

introduces crosstalk in the optical communication

system like wavelength division multiplexing

system [5]. Thus we need to minimize these

nonlinear effects because these are the major

limiting factors. FWM is a parametric process in

which different wavelengths interrelate and by

frequency collaborating produce new false spectral

component [6].When we increases the value of

chromatic dispersion the value of FWM nonlinear

effects decreases.

Figure 2 ‘‘block diagram of four wave mixing’’

2 Simulation Work

We studied the FWM, XPM and SPM effects by

varying length, dispersion and power. We can

alleviate these by using these parameters and

overwhelmed the nonlinear effects. A system for

FWM is analyzed by using operating frequency

193.025 to 193.075 THz and power varied from 7

mw to 17 mw, fiber length is varied from 50 km to

100 km and dispersion is varied from 0 to 10

ps/nm/km. Spectrum analyzer in the optical domain

has been used to view the input signal and output

signal at the output of the fiber. A system for SPM

is analyzed by using operating wavelength 1552 nm

and power varied from 25 mw to 45 mw, length

varied from 40 km to 120 km and dispersion varied

from 0 to 4 ps/nm/km.

2.1 SPM analysis and results

An Optical Spectrum Analyzer (or OSA) is an

instrument used to measure and display the

scattering of power of an optical source over a

quantified wavelength duration.



IJETSR

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ISSN 2394 – 3386

Volume 4, Issue 6

June 2017

Figure 3 ‘‘Input signal of self-phase

modulation’’

Figure 4 ‘‘Output signal of self-phase

modulation’’

Eye diagrams of self-phase modulation. We taking

these eye diagrams by using electrical scope .An

eye diagrams are generated by an oscilloscopes by

overlaying sweep. The value of Q-factor should be

6 in linear and 16 in dB for better performance.

From the eye diagrams we conclude that by

increasing the dispersion eye opening becomes

good and the quality factor will be improve and the

value of BER will be decrease.

Figure 5 ‘‘Eye diagram for length 10 km and

power 12 mw’’


power 12 mw’’

Q-factor in the optical fiber communication defines

the quality of a signal to be received at the output

side.

In the optical fiber communication system q-

factor provides straight impression on the FWM

system performance. This Q-factor is demarcated

by the proportion of signal power to noise power at

the optical receiver of a system. Q-factor of SPM is

decreasing as we increasing the length at different-2

powers.



IJETSR

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ISSN 2394 – 3386

Volume 4, Issue 6

June 2017

Figure 7 ‘‘Q-factor vs. length of self-phase

modulation’’

BER is the no. of bits transmitted per unit time. It is

also called bit error ratio. BER of SPM is increasing

as we increasing the length at different-2 powers.

The value of BER will be decreases with increase in

dispersion. It should be below than to achieve

good performance.

Figure 8 ‘‘BER vs. length of self-phase

modulation’’

2.2 FWM analysis and results

Input spectrum taking through input optical

spectrum analyzer and output spectrum through

output spectrum analyzer.

Figure 9 ‘‘Input signal of self-phase

modulation’’

Figure 10 ‘‘Output signal of self-phase

modulation’’

Eye diagrams of four wave mixing. An eye

diagram defines the quality of signal to be

transmitted in high speed transmission or defines

the quality of signal received at the output.

Commencing the eye illustrations we conclude that

via increasing the length eye opening becomes bad

and the quality factor degrade and the worth of BER

will be decrease.



IJETSR

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ISSN 2394 – 3386

Volume 4, Issue 6

June 2017


power 5 mw’’

Figure 12 ‘‘Eye diagram for length 70km and

power 5 mw’’

In the fiber-optic communication system q-factor

gives direct impact on the FWM system

performance. Q is decreasing as we increasing the

length at different-2 powers and taking dispersion

constant 9 ps/nm/km.

Figure 13 ‘‘Q-factor vs. length of four wave

mixing’’

BER is the no. of bits transmitted per unit time or it

is also called bit error ratio.it is the ratio of bit

errors to the total no. of transmitted bits. BER of

FWM increases as we increases length at differernt-

2 powers and taking dispersion constant 9

ps/nm/km.

Figure 14 ‘‘BER vs. length of four wave mixing’’



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 6

June 2017

3 CONCLUSION

In this paper we accomplish that by changing

parameters length, power and dispersion the Q-

factor and BER varies and determine the

performance of system. When we Increases

dispersion in FWM and XPM, Q-factor and BER

improved. The sysyem with NRZ modulation

format shows good result up to 120 km distance for

optical fiber communication. At distance above 120

km BER is very high and quality factor is not so

good. BER of value 6.82031e-024 is found to be at

length 120, power 12mw and dispersion 9

ps/nm/km. If we enlarged the value of dispersion

the quality factor found to be 9.302949 to 22.90325

dB, for length value of quality factor 28.335732 to

18.291495 dB and for power 28.260082 to

31.351132 dB.

4 REFERENCES [1] G.P. Agarwal, nonlinear fiber optics, 3rd edition,

Academic press, San Diego, CA, 2001.

[2] Sharddha N.Bhusari, Vikas U.Deshmukh,

Analysis of Self-Phase Modulation and Four-

Wave Mixing in Fiber Optic Communication,

IEEE, 2016.

[3] G.P. Agarwal, fiber optic communication

system, 3rd edition, New York: Wiley, 2002.

[4] S.P.Singh, N.Singh, nonlinear effects in optical

fiber, PIER73, 249-275, 2007.

[5] Fahd CHAOUI3, Otman AGHZOUT, Ana

Vazquez ALEJOS, Francisco FALCONE,

Mounia CHAKKOUR, Mounir EL

YAKHLOUFI, Reduction of Four-Wave

Mixing Nonlinear Effects in Dense WDM

Optical Long-Haul Networks, IEEE, 2016.

[6] Jiangbing Du, Lu Li, Xinyu Fan, Qingwen Liu

and Zuyuan He, Sensitivity Enhancement for

Fiber Bragg Grating Sensors by Four Wave

Mixing, Photonics, 2, 426-439; 2015

[7] Mohammad Faisal, Influence of XPM in

Periodically Dispersion Managed WDM

Transmission Systems, ICECE 2010, 18-20

December 2010, Dhaka, Bangladesh.

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