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20120140503003
- 1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
21
WDM TRANSMISSION IN L-BAND OVER CONVENTIONAL SINGLE
MODE FIBER WITH 27.2-dB SPAN LOSS CONSIDERING NON-
LINEARITIES AND ASE NOISE
Niyati A. Maniar, Rohit B. Patel
Dept. of Electronics & Communication Engineering, Ganpat University, Kherva, India
ABSTRACT
We have report the transmission of twenty 10-Gb/s channels and twenty 20-Gb/s with 100-
GHz spacing over 80 km spans of Conventional single mode fiber in the lower wavelength region of
L-band. Low error rates are achieved with 2.5 dBm input power per channel and a span loss of 27.2
dB. For large transmission distances it covers 320 km for 400-Gb/s and 720 km for 200-Gb/s with
acceptable bit error rate using pre and post-dispersion compensation technique. It was also observed
that post compensation provides better performance compare to pre-compensation method.
Keywords: BER, Conventional Single Mode Fiber, Dispersion Compensation, Q-Factor,
Wavelength Division Multiplexing.
I. INTRODUCTION
Optical fibers are used for data transmission in optical fiber communication system. In optical
fiber data flows in form of light. Recently, the traffic over transmission lines has increased rapidly.
With a view of enlarging the transmission line capacity, increasing attention has been directed
toward wavelength-division multiplexing (WDM) techniques and higher bit-rate transmissions of
more than 40-Gb/s. Wavelength division multiplexing (WDM) can give two benefits at the same
time: enhancement of transmission capacity and increase in flexibility in optical network design [1].
It is possible to build long-distance transparent optical transmission links without electrical
regenerators with the help of erbium-doped fiber amplifiers (EDFAs). EDFA plays an important role
to avoid the losses in the signal. EDFA has been used as booster and inline amplifier to transmit
optical signals over thousands of kilometers. EDFAs are having of low noise figure and have a good
gain bandwidth and can amplify multichannel signals on different wavelengths simultaneously, so
EDFA emerges as the implementing technology for WDM systems [2]. Although the use of optical
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
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ISSN 0976 - 6480 (Print)
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- 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
22
amplifiers has extended the optical network dimensions to thousands of kilometers and made the
concept of transparent optical networks quite feasible, at the same time their use introduces some
problems like accumulation of amplified spontaneous emission (ASE) noise generated by inline
optical amplifiers and aggravation of fiber nonlinearity effects such as stimulated Raman scattering
(SRS) and four-wave mixing (FWM). In such systems, apart from the usual problems of fiber loss
(amplifier noise) and dispersion, fiber nonlinearities are likely to impose a transmission limit due to
the increased total interaction length [3].System specifications such as total transmission distance,
amplifier spacing, the number of WDM channels, the channel spacing and the power per channel are
all affected by the fiber nonlinear effects. The performance of optical fiber is limited by the factor
known as dispersion.
When optical signals are transmitted over optical links, different wavelength components
of the optical signals will generally experience different propagation times due to the fact that the
transport medium (such as an optical fiber) has different effective refractive indices for different
wavelengths. This phenomenon is referred to as dispersion, or chromatic dispersion. As a result of
dispersion, an optical pulse, which always has some finite width in wavelength, will be
broadened, since different wavelength components of the pulse will travel at slightly different
group velocities through the optical link. Such broadening of optical pulses caused by the
dispersion may lead to a situation at the receiver end where it is difficult to separate adjacent pulses
from each other during detection which leads to errors in receiver and correct reception of bits.
Moreover, dispersion compensation over a wide wavelength range is particularly needed for WDM
transmissions. Dispersion-shifted fibers, dispersion-flattened fibers, dispersion decreasing fibers,
DCFs (dispersion compensating fiber) are used for dispersion compensation in optical
communication system. DCF is the type of fiber that has the opposite dispersion (negative
dispersion) of the fiber (positive dispersion) being used in a transmission system. It is used to nullify
the positive dispersion of the fiber [4, 5]. Particularly for high modulation rate systems,
dispersion becomes a severely limiting factor. The transmission impairment caused by dispersion
in a single mode fiber (SMF) is severe for such high-bit-rate transmissions. For this reason, it is
typically required to use some kind of dispersion compensation along the optical link and/or at
the receiver side. This has made dispersion-compensation techniques essential, and a dispersion-
compensation fiber (DCF) is widely used. Various DCFs that were optimized to compensate for the
dispersion in a single band, e.g., the S-band (1460–1530 nm), C-band (1530–1565 nm), and L-band
(1565–1625 nm), have been reported, and they were obtained by matching the relative dispersion to
slope (RDS) of the DCF to that of the transmission fiber. It has also been reported that combining
two or more DCFs can realize broadband compensation from the C-band to the L-band. However, it
is difficult for the DCF to compensate for dispersion over the O-band (1260–1360 nm) or the E-band
(1360–1460 nm). This is because the material dispersion has a strong effect. It is therefore difficult to
control the dispersion over all the telecommunication bands [6].The maximum possible transmission
distance depends on various system parameters like number of channels, channel spacing, allowable
power per channel, amplifier spacing, etc. With Reference to paper [7], reported the transmission of
twenty 10-Gbps channels with 100-GHz spacing over four 80-km spans of dispersion-shifted fiber in
the lower wavelength region of L-band. They have used dispersion shifted fiber with core size of 50
µm^2 with pre-dcf compensation technique. The loss per Span was kept 25 dB. The BER obtained
was <10^ (-12) for 200-Gb/s. In this letter, we report low error rate transmission <10^(-15) of twenty
10-Gb/s and <10^(-12) 0f twenty 20-Gb/s channels with 100-GHz spacing over 80 km spans of
conventional single mode fiber having core size of 80 µm^2, each with a span loss of 27.2 dB using
pre and post compensation. Also, non-linearities effect and ASE noise is considered. We choose
operation in the lower wavelength region of the L-band.
- 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
23
II. DATA MODULATION FORMAT
An optical modulation format is the method used to impress data (i.e., information) on
an optical carrier wave for transmission over optical fiber or any other any other media such as free
space, nano photonic optical waveguide, etc. In conventional single mode optical fibers, the optical
field has three physical attributes that can be used to carry information: intensity, phase (or
frequency) and polarization. Depending upon which of the three quantitative is used for information
transport, we distinguish between intensity, phase (or frequency) and polarization data
modulation formats. This classification does not require a phase modulated optical field to be
constant envelope, nor an intensity modulated field to have constant phase. It is the physical
quantity used to convey data information that drives the classification. The simplest optical
modulation format is on-off keying (OOK) intensity modulation, which can take either of two
forms: non return to zero (NRZ) or return Zero (RZ).We have used NRZ format. The advantages of
using NRZ data modulation formats include its low electrical bandwidth requirement,
insensitivity to laser phase noise and simplest configuration of transceivers. The reduced
spectrum width improves the dispersion tolerance. In the NRZ format the function that describes the
voltage pulse is given by [8]:
V(t)=Von-off [1-exp(-t/trise)^2] Vm=Von
V(t)=Von-off[exp(-t/trise)^2] Vm=Voff
Where Von-off=Von-Voff= -2mVbias and trise is the circuit rise time that determines the 3dB
modulation bandwidth BW.
III. SIMULATION SET-UP
The schematic block diagram of the proposed 20-channel 10-Gb/s and 20-Gb/s WDM link
using pre and post and compensation technique is shown in Fig.1 respectively. The dispersion
compensation is done using pre and post-compensation techniques depending on the position of
Dispersion Compensating Fiber (DCF). Pre-Compensation: In this Compensation scheme, the
dispersion compensating fiber of negative dispersion is placed before the standard fiber to
compensate positive dispersion of the standard fiber. Post-Compensation: In this Compensation
scheme, the dispersion compensating fiber of negative dispersion is placed after the standard fiber to
compensate positive dispersion of the standard fiber [5, 6, 9]. The WDM transmitter consists of 20
channels which is spaced by 100 GHz from 1574.6 to 1590.31 nm using CW laser and are combined
using Wavelength Division Multiplexer (WDM). The modulation format used is Non Return to Zero
(NRZ). The power per channel launched at the start of every span was 2.5 dBm which was found
optimum for minimum effect of non-linearities. One span of link consists of conventional single
mode fiber, EDFA and dispersion compensating fiber. A 80 km SMF which has a dispersion of
17ps/nm/km would encounter a total of (80 x 17) 1360ps/nm of dispersion. Assuming the DCF has a
negative dispersion of -85 ps/nm/km, and then 16km (1360ps/nm ÷ 85ps/nm/km) of DCF is needed
for the compensation. A matched-cladding type DCF has a positive dispersion slope similar to
transmission fibers and the dispersion slope of the DCF is steeper than that of the conventional
single-mode fiber [5]. When this type of DCF is used for dispersion compensation, the dispersion
slope for the whole transmission system including the DCF becomes larger than that for the
transmission fiber alone and a wavelength region where the dispersion is well compensated is
restricted to a narrow range. The gain of the erbium doped fiber amplifier (EDFA) placed after each
fiber is such that is compensates the losses of the preceding fiber. The noise figure of the amplifiers
is constant and set to 4 dB. The Overall loss for each span is 27.2 dB including dispersion
- 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
24
compensator loss. The non-linearities effect of conventional single mode fiber and ASE noise of
EDFA is also taken in to account. The simulation parameters and fiber parameters used in the system
model are mentioned in Table 1. The channels at the receiver side are demultiplexed using
Demultiplexer. At the end of the link the channels are detected with a p-i-n receiver and low pass
Bessel filter with order two is used. The dark current and responsivity of the PIN diode is taken as 10
nA and 1 A/W respectively. 3R regenerator is used to generate an electrical signal, connected
directly to the BER analyzer which is used to visualize the graphs and results such as eye diagram,
eye opening, the Q value and BER. The experiment is carried out for two different data rates (a)
Each channel is modulated at 10-Gb/s, so total data rate is 200-Gb/s. (b) Each channel is modulated
at 20-Gb/s, so total data rate is 400-Gb/s.
(a)
(b)
Fig.1: Schematic of simulation setups: (a) using pre-compensation (b) using post-compensation
- 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
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IV. RESULTS
For 200 Gb/s and 400 Gb/s, the simulation was carried out for pre and post-compensation.
The result was compared in terms of Q value, BER and eye-diagram. Q-factor can be defined as ratio
of Signal to Noise Ratio (SNR) versus transmission distance per symbol. The bit error rate (BER) is
the percentage of bits that have errors relative to the total number of bits received in a transmission,
usually expressed as ten to a negative power. Eye diagram is used to visualize how the waveforms
used to send multiple bits of data can potentially lead to errors in the interpretation of those bits. This
is the so-called problem of intersymbol interference. It was found that post compensation performed
better than pre-compensation technique. The total distance covered is 720(9X80) for 200-Gbps and
320km (4X80) for 400-Gbps considering only conventional single mode fiber. The Q versus
wavelength for all twenty channels wavelength for 200-Gb/s using pre-compensation and post-
compensation method is plotted in Fig.2 respectively. The measured BER versus wavelength for all
twenty channels for 200-Gb/s using pre-compensation and post-compensation method are plotted in
Fig.3 respectively.
TABLE 1: Parameters used in simulation
Parameter Value
Total Channels 20
Bit-Rate 200,400 Gb/s
Channel Spacing 100-GHz
Length of SMF 80 Km
Length of DCF 16 Km
Dispersion coefficient of SMF 17 ps/nm/km
Dispersion coefficient of DCF -85 ps/nm/km
Gain of Inline EDFA for SMF 24 db
Gain of Inline EDFA for DCF 3.2db
Attenuation factor of SMF 0.2 db/km
Total Span 9 for 200-Gbps,4 for 400-Gbps
Total Distance covered
720 for 200-Gbps
320 km for 400-Gbps
The Q versus wavelength for all twenty channels wavelength for 400 Gb/s using pre-
compensation and post-compensation method are plotted in Fig.4 respectively. The measured BER
versus wavelength for all twenty channels for 400-Gb/s using pre-compensation and post-
compensation method are plotted in Fig.5 respectively. The Bold letters in the table indicates the
improvement of wavelength in terms of Q-factor and BER for post- compensation scheme over pre-
compensation scheme. It was found that, for 200- Gb/s, for wavelength 1574.6 nm, Q-factor for pre-
compensation is 11.84 and BER is 1E-32 and for post-compensation Q-factor is 15.08 and BER is
1.02E-51 respectively. Similarly, for 400-Gb/s for wavelengths 1574.6 nm, Q-factor for pre-
compensation is 7.19 and BER is 2.56E-13 and for post-compensation Q factor is 8.09 and BER is
2.7E-16. The table and graph clearly indicates the post scheme performs significantly better than pre-
scheme compensation. The performance of the lower wavelength channels is seen to be lesser than
that of the longer wavelength channels. This is likely due to a combination of larger FWM and CPM,
together with some overcompensation of dispersion. Comparison between pre and post-scheme in
terms of Q factor and BER for 200-Gb/s and 400-Gb/s is given in Table 2 and 3 respectively.
- 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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TABLE 2: Comparison between pre and post-compensation scheme for 200-Gb/s over 4 spans
TABLE 3: Comparison between pre and post-compensation scheme for 400-Gb/s over 4 spans
For200-Gb/s
(320Km) Pre-compensation Post-compensation
wavelength Q-Factor BER Q-Factor BER
1574.6 11.84 1E-32 15.08 1.02E-51
1575.42 14.1 1.55E-45 14.32 6.41E-47
1576.25 11.66 8.49E-32 14.5 5.81E-48
1577.08 11.96 2.42E-33 12.05 8.1E-34
1577.9 10.81 1.29E-27 11.81 1.49E-32
1578.73 11.18 2.08E-29 13.51 5.72E-42
1579.56 12.46 5.1E-36 13.46 1.08E-41
1580.38 13.03 3.47E-39 11.67 7.53E-32
1581.21 11.47 7.21E-31 12.29 4.09E-35
1582.04 12.17 1.61E-34 12.34 2.3E-35
1582.87 12.03 1E-33 12.59 9.79E-37
1583.69 11.02 1.24E-28 11.72 4.23E-32
1584.52 13.31 7.93E-41 13.27 1.53E-40
1585.35 11.61 1.43E-31 14.19 4.69E-46
1586.17 10.4 9.53E-26 11.6 1.64E-31
1587 10.91 3.95E-28 11.86 7.45E-33
1587.83 11.05 8.9E-29 11.54 3.32E-31
1588.65 12.11 3.66E-34 13.6 1.54E-42
1589.48 11.2 1.52E-29 12.09 4.88E-34
1590.31 12.67 3.19E-37 14.4 2.04E-47
For400-Gb/s
(320Km) Pre-compensation Post-compensation
wavelength Q-Factor BER Q-Factor BER
1574.6 7.19 2.56E-13 8.09 2.7E-16
1575.42 8.79 6.15E-19 9.44 1.66E-21
1576.25 8.59 3.75E-18 8.8 5.93E-19
1577.08 8.03 4.06E-16 9.09 4.01E-20
1577.9 7.69 6.1E-15 7.65 8.69E-15
1578.73 8.21 9.56E-17 8.67 1.99E-18
1579.56 8.06 3.04E-16 9.17 2E-20
1580.38 8.56 4.72E-18 8.4 1.97E-17
1581.21 7.6 1.17E-14 9.04 6.5E-20
1582.04 7.41 4.89E-14 7.89 1.39E-15
1582.87 7.49 2.88E-14 8.01 4.95E-16
1583.69 7.12 4.66E-13 7.71 5.55E-15
1584.52 6.9 2.2E-12 7.78 3.27E-15
1585.35 9.35 3.67E-21 9.74 9.15E-23
1586.17 7.68 7.06E-15 7.63 1.04E-14
1587 6.81 3.95E-12 8.26 6.7E-17
1587.83 6.99 1.14E-12 8.3 4.48E-17
1588.65 7.52 2.15E-14 8.32 3.75E-17
1589.48 6.9 2.31E-12 7.38 7.09E-14
1590.31 9.06 5.81E-20 9.08 4.9E-20
- 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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27
(a)
(b)
Fig.2: Q versus Wavelength for 200-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
0
2
4
6
8
10
12
14
16
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
0
2
4
6
8
10
12
14
16
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
- 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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(a)
(b)
Fig.3: BER versus Wavelength for 200-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
1570 1575 1580 1585 1590 1595Log(BER)
Wavelengtth
BER
-60
-50
-40
-30
-20
-10
0
1570 1575 1580 1585 1590 1595
Log(BER)
Wavelength
BER
- 9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 21-36, © IAEME
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(a)
(b)
Fig.4: Q versus Wavelength for 400-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
0
1
2
3
4
5
6
7
8
9
10
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
0
2
4
6
8
10
12
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
- 10. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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(a)
(b)
Fig.5: BER versus Wavelength for 400-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
-25
-20
-15
-10
-5
0
1570 1575 1580 1585 1590 1595
Log(BER)
Wavelength
BER
-25
-20
-15
-10
-5
0
1570 1575 1580 1585 1590 1595
Log(BER)
Wavelength
BER
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We also considered for the distance extension for two data rates 200 and 400-Gb/s. It was
found that distance extended to 720 km with acceptable BER for 200-Gb/s but increasing distance
for 400-Gb/s Q-value degrades and BER increased to 10^(-7) which shows that increasing data rate,
dispersion and non-linearities increases. For 200-Gb/s, simulation was carried out for pre and post-
compensation scheme. The post-scheme performed better compare to pre scheme. The Q versus
wavelength for all twenty channels wavelength for 200-Gb/s for nine spans (80x9 km) using pre-
compensation and post-compensation scheme are plotted in Fig.8 respectively. The measured BER
versus wavelength for all twenty channels for 200-Gb/s for nine spans (80x9 km) using pre-
compensation and post-compensation method are plotted in Fig.9 respectively. The Eye diagram of
first channel (1574.6nm) for pre and post-compensation for 200-Gb/s for nine spans is shown in
fig.10. Comparisons between pre and post-scheme in terms of Q factor and BER for 200- Gb/s over
nine spans are given in Table 4. The Bold letters in the table indicates the improvement of
wavelength in terms of Q-factor and BER for post compensation scheme over pre-compensation
scheme. To analyze the system, the results of the first channel have been taken. The Eye diagram of
first channel (1574.6nm) for pre and post-compensation for 200-Gbps for four spans is shown in
fig.6. The Eye diagram of the pre and post-compensation for 400-Gb/s for four spans is shown in
fig.7.The figure clearly shows that eye opening decreases with increase in data rate.
(a)
(b)
Fig.6: Eye Diagram (for first channel) for 200-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
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TABLE 4: Comparison between pre and post-compensation scheme for 200-Gb/s over 9 spans
(a)
(b)
Fig.7: Eye Diagram (for first channel) for 400-Gb/s over 4 spans
(a) for pre-compensation (b) for post-compensation
For 200-Gb/s
(720Km) Pre-compensation Post-compensation
wavelength Q-Factor BER Q-Factor BER
1574.6 6.35 8.48E-11 7.85 1.73E-15
1575.42 8.93 1.62E-19 9.09 4.1E-20
1576.25 8.69 1.51E-18 8.83 4.31E-19
1577.08 6.62 1.43E-11 8.16 1.41E-16
1577.9 6.87 2.43E-12 9.02 7.88E-20
1578.73 5.91 1.23E-09 7.24 1.97E-13
1579.56 7.7 5.17E-15 9.65 1.98E-22
1580.38 8.26 5.76E-17 8.68 1.59E-18
1581.21 6.92 1.68E-12 8.09 2.57E-16
1582.04 6.51 2.74E-11 7.13 4.33E-13
1582.87 7.15 3.48E-13 8.29 4.85E-17
1583.69 7 9.8E-13 7.38 6.44E-14
1584.52 6.85 2.59E-12 9.01 8.81E-20
1585.35 7.09 4.98E-13 8.93 1.66E-19
1586.17 7.05 6.7E-13 8.58 3.95E-18
1587 6.91 1.87E-12 8.07 2.87E-16
1587.83 6.24 1.75E-10 9.07 4.91E-20
1588.65 5.76 3.3E-09 7.96 7.19E-16
1589.48 7.55 1.75E-14 7.37 7.03E-14
1590.31 7.7 5.14E-15 9.71 1.07E-22
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(a)
(b)
Fig.8: Q versus Wavelength for 200-Gb/s over 9 spans
(a) for pre-compensation (b) for post-compensation
0
1
2
3
4
5
6
7
8
9
10
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
0
2
4
6
8
10
12
1570 1575 1580 1585 1590 1595
Q
Wavelength
Q
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-25
-20
-15
-10
-5
0
1570 1575 1580 1585 1590 1595
Log(BER)
Wavelength
BER
(a)
(b)
Fig.9: BER versus Wavelength for 200-Gb/s over 9 spans
(a) for pre-compensation (b) for post-compensation
-25
-20
-15
-10
-5
0
1570 1575 1580 1585 1590 1595Log(BER)
Wavelength
BER
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(a)
(b)
Fig.10: Eye Diagram (for first channel) for 200-Gb/s over 9 spans
(a) for pre-compensation (b) for post-compensation
V. CONCLUSION
In this paper, we have demonstrated WDM transmission of twenty channels modulated at 10-
Gbps and 20-Gbps data rate in the in the lower wavelength region of the L-band using conventional
single mode fiber. Each span having a span loss of 27.2 dB was taken considering non-linearities and
ASE noise. The total distance covered for 200-Gb/s was nine span (720km) with acceptable BER
<10^(-15) and four spans (320km) for 400-Gbps with acceptable BER <10^(-12) by post-
compensation scheme, which clearly shows that increasing data rate limits the transmission distance
due to increase in non-linearities and dispersion. Also, the simulation was performed for both 200
and 400-Gb/s using pre and post compensation techniques and it was found that post compensation
scheme performs better than pre compensation scheme.
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REFERENCES
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