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
39 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
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.
40 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
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’’
Figure 6 ‘‘Eye diagram for length 15 km and
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.
41 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
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.
42 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
Figure 11 ‘‘Eye diagram for length 50 km and
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’’
43 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
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.