Download III. results and discussions

International Conference On Emerging Trends In Engineering, 14th October 2012
ICETIE/146
Optimal Design of Long Haul Optical
Communication Link Operating at 10 Gbps
Munish Kumar1, Varun Jain2, Laxya3

Abstract— An optical communication system operating
at 10 Gbps based on fiber Bragg grating is presented in
this paper. Dispersion has been a main limiting factor in
optical communication transmission system. The use of
FBG as dispersion compensator shows improved
transmission
performance
in
optical
fiber
communication system. This paper simulates the optical
communication system to investigate the effect of
dispersion and also measured the performance
parameters such as BER, Q factor and eye diagram at
2500 km transmission distance.
II. SYSTEM DESCRIPTION
A model of optical communication system is simulated as
shown in Fig. 1. First, we design a simulation setup that
Index Terms—BER, Dispersion Compensation, Eye
diagram, FBG and Q-factor.
Fig. 1 Simulation set up for Dispersion compensation system
I. INTRODUCTION
In order to make communication over a long distance
with larger transmission capacity and longer repeaterless
distance, it is very important to restrain the dispersion effect
and nonlinear effects such as self-phase modulation (SPM),
cross-phase modulation (XPM) and four wave mixing
(FWM) [1]. In optical communication fiber loss is mainly
controlled by erbium doped fiber amplifiers (EDFA). In
long haul transmission many technologies have been
adopted to reduce the effect of noise, nonlinearity effect,
dispersion and also to enhance the quality of optical signal
[2]. FBG has been used to enhance the system performance
by compensating the dispersion in single mode fiber. This
paper describes the design based on single mode fiber,
EDFA and FBG for dispersion compensated transmission.
1Munish Kumar is with the Guru Jambheshwar University of Science
and
Technology,
Hisar,
125001INDIA.
(e-mail:
[email protected])
2Varun Jain is with the Ambedkar Institute of Advanced
Communication Technologies and Research (GGSIPU) Geeta Colony,
New Delhi-110031 INDIA. (e-mail: [email protected])
3Laxya is with Netaji Subhash Institute of Technology (University of
Delhi),
Sec-3,
New
Delhi-110078
INDIA.
(e-mail:
[email protected])
Fig. 2 System defined inside the iteration loop
defined in a iteration loop where FBG is used to compensate
the dispersion of single mode fiber. The 10 Gbps signal
applied at the input generated by CW lorentzian laser source,
modulated by machzehnder modulator and transmitted over
a distance of 2500 km [3]. The transmission link is
composed of fiber spans of 100 km and repeated over 25
times by loop control. Single mode non linear fiber is
followed by EDFA the amplifier and FBG the dispersion
compensator defined in loop control shown in Fig. 2.
In this simulation model NRZ modulation format is
employed. Then signal passed through single mode fiber
and then amplified by the EDFA. Then the optical signal
entered the FBG for dispersion compensation and later into
the loop control for 2500 km transmission. At the receiver,
International Conference On Emerging Trends In Engineering, 14th October 2012
ICETIE/146
pin-photodiode has been used to convert the optical signal
into electrical signal. PIN diode with quantum efficiency of
0.7 and -3dB of 40 GHz with dark current of 1 nA [4].
III. RESULTS AND DISCUSSIONS
Following the simulation set up described in section 2,
the effect of dispersion has been investigated on long haul
optical transmission system. The eye diagrams of the signal
for D=17 ps/nm-km at 100 km with and without dispersion
compensation are shown in Fig. 3, 4 and 5, respectively. The
effect of using FBG as dispersion compensator has been
measured by comparing the two eye diagrams shown in Fig.
3 and Fig. 4 also, by comparing the BER and Q-factor.
(a)
(b)
Fig. 5 Eye Diagram obtained after dispersion compensation
at (a) 1600 and (b) 2500 km
Fig. 3 Eye Diagram obtained before dispersion compensation
at 100 km
We observed from the fig. 3, that the avg. eye opening
before dispersion compensation is 3.1376*e-006 a.u, Q-factor
is 11.6 dB and BER is 10-05. Eye diagrams are obtained at
wavelength of 1550 nm, input bit rate of 10 Gbps and input
power of 5 dB. It is concluded from the result that, the value
of avg. eye opening decreases continuously as the optimal
distance increases.
Eye diagram after dispersion compensation is obtained at
a transmission distance of 100 and 1600 km, shown in fig 4
and fig. 5(a) and avg. eye opening measured from the eye
diagram are 0.002232 and 0.002013 a.u. Avg. eye opening
at a distance of 2500 km, after compensation is also
obtained from the eye diagram as shown in fig. 5 (b), is
0.001869 a.u. Eye diagrams are obtained at wavelength of
1550 nm, input bit rate of 10 Gbps and input power of 5 dB.
It is concluded from the result that, the value of avg. eye
opening decreases continuously as the optimal distance
increases.
The eye diagram obtained by electrical scope shown in
Fig. 5 (b) representing dispersion compensated output at
2500 km transmission distance. The BER and Q-factor thus
obtained are 10-16 and 18.17 dB respectively, using NRZ
modulation format. The input power has been taken as 5 dB
and duty cycle has been taken as 0.5.
Table I Performance parameters at different distances after
compensation at 10 Gbps, using NRZ format at 5 dB input power
Fig. 4 Eye Diagram obtained after dispersion compensation
at 100 km
Distance
(km)
100
BER
10-40
Q-Factor
(dB)
40
Avg. Eye
Opening [a.u]
0.002232
1600
7.02*10-39
22.35
2500
9.36*10-16
18.17
0.002013
opooooopen
0.001869
3200
4.7*10-10
15.66
0.001791
International Conference On Emerging Trends In Engineering, 14th October 2012
ICETIE/146
In table I value of different performance parameters such
as BER, Q-factor and Eye diagram over different distances
is shown.
The effect of increase in transmission distance on
performance parameters such as BER and Q-factor at 10
Gbps are shown by graphs, as explained as follows:
10
-40
long distance communication system with NRZ at 10 Gbps,
the BER and Q-factor for the system are 10-16 and 18.17 dB,
over a distance of 2500 km. The BER increases with the
increase in distance, while q-factor decreases. The FBG
used in simulation model have uniform grating pattern to
compensate the dispersion and other non linearities. It is
concluded that Q-factor decreases with the increase in
distance
REFERENCES
-30
BER
10
10
10
-20
-10
0
500
1000
1500
2000
2500
3000
3500
2000
2500
3000
3500
DISTANCE
(a)
40
Q-FACTOR(dB)
35
30
25
20
15
10
5
0
500
1000
1500
DISTANCE
(b)
Fig. 6 Graphs of Distance vs (a) BER and (b) Q-factor
The variation of performance parameters such as BER
and Q-factor with distance is shown in figure 6 (a) and (b),
respectively. It is obtained from the figure 6 (a), that BER
remains constant upto a distance of 1200 km, thereafter it
increases continuously. BER obtained at a distance from
100 to 1200 km is 10-40 and increased to 10-10 over a distance
of 3200 km. It is obtained from the figure 6 (b), Q-factor
also varies with the distance. The Q-factor decreases from
40 to 15.66 dB as a distance increases from 100 to 3200 km.
The performance of the system is represented by eye
diagram. The attenuation coefficient used for SMF is
0.2dB/km. Dispersion has been taken as 17 ps/nm/km and
dispersion slope has been taken as 0.07 ps/nm2/km. The non
linear index coefficient of 2.6x10-20 m2/w has been taken.
The FBG used in simulation model have uniform grating
pattern. NRZ have duty cycle of 0.5.
IV. CONCLUSION
It has been investigated from the simulation results of the
long haul optical link operating at 10 Gbps input bit rate,
that the system is better in terms of BER and Q-factor. For
[1] Wen Liu, Shu-qin, Lin-ping Chang, Ming Lei, Fu-mei Sun,
“The research on 10 Gbps optical communication dispersion
compensation systems without electric regenerator”, IEEE,
3rd international conference on image & signal processing
(CISP 2010).
[2] H.Taga, S-S.Shu, J.-Y. Wu, and W.-T. Shih, “A theoretical
study of the effect of the dispersion map upon a long haul
RZ-DPSK transmission system,” IEEE Photon Technology
Letter, vol. 19, pp. 2060-2062, December (2007).
[3] Wen Liu, Shu-qin GUO, “The optimal design of 2500 km -10
Gb/s optical communication dispersion compensation
systems without electric regenerator,” IEEE, international
conference on electrical & control engineering (2010).
[4] S. Al-Mamun and M.S.Islam, “Effect of Chromatic
Dispersion on four-wave mixing in optical WDM
transmission System,” ICIIS, Aug. 16-19, 2011.