Simulative analysis of power effects for 2.5×8 gbs wdm pon

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-
6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 3, May – June (2013), © IAEME
220
SIMULATIVE ANALYSIS OF POWER EFFECTS FOR 2.5×8GB/S
WDM-PON SYSTEM FOR CSRZ, DRZ AND MDRZ DATA FORMATS
Malti1
, Rajesh Luther2
and Rakesh Sharma3
1, 2, 3
Sri Sai Institute of Engg. & Tech., Amritsar, Punjab, India
ABSTRACT
In this paper, simulative analysis of 2.5×8Gb/s WDM-PON system has been carried
out for carrier suppressed return to zero (CSRZ), duobinary return to zero (DRZ) and
modified return to zero (MDRZ) modulation formats by varying power effects (0-20dBm). It
is observed that the system gives optimum performance at input power Pin = 20dBm. It is
found that CSRZ gives more optimum performance as compared to DRZ and MDRZ when
Pin = 20dBm. Further, the effect of variation in input power Pin and transmission distance up
to 130km has been observed in terms of Q-value and Max. eye opening factor for CSRZ,
DRZ and MDRZ modulation formats. The system performance has been also evaluated by
varying bit rate at 2.5Gb/s, 5Gb/s and 10Gb/s and it is observed that the system gives best
results at bit rate 2.5Gb/s.
Keywords: WDM-PON, CSRZ, DRZ, MDRZ, OLT, ONU.
I. INTRODUCTION
To meet the bandwidth demand due to the exponential growth of broadband services,
WDM-PON will be one of the most efficient way for the next generation access network. To
meet the increasing demand of network bandwidth, Service Provider (SP) must provide
broadband services to many subscribers. In traditional PON, the number of ONUs is limited
by optical splitter attenuation in a single wavelength. However, combining WDM technology
with PON architecture will provide even hundreds of wavelengths in an access network, so
WDM-PON is considered an effective way to solve the bottleneck problem to have large
numbers of end users [1]. Much attention has been focused on the wavelength division
multiplexed passive optical network (WDM-PON) for next-generation broadband access
architecture, due to its large bandwidth, upgrade flexibility and security with dedicated
INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING
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ISSN 0976 – 6367(Print)
ISSN 0976 – 6375(Online)
Volume 4, Issue 3, May-June (2013), pp. 220-228
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221
connections. A WDM-PON solution provides scalability because it can support multiple
wavelengths over the same fiber infrastructure, is inherently transparent to the channel bit
rate, and it does not suffer power-splitting losses.
Bock et al. [2] described WDM/TDM-PON architecture by using Free Spectral Range
(FSR) periodicity and AWG. In this a shared tunable laser, photo receiver, DBA and remote
modulation were used for transmitter and receiver. Transmission test showed correct
operation at 2.5Gb/s up to 30km. By mean of optical transmission test the authors
demonstrated that this architecture was feasible and offered good performance with low
optical losses as compared to other PON architectures.
Yi-Hung Lin et al. [3] demonstrated AWG Channel bandwidth dependent BER power
penalty of 8 dB for the 1.25Gbit/s DWDM-PON systems with channel spacing of 50 and 200
GHz using ASE injection-locked reflective SOA with 1% front-facet reflectance. Even
though the color-free operation had not yet been realized due to high front facet reflectivity,
they had shown that the nearly mode independent operation of such a RSOA based
DWDMPON with 50-GHz AWG mode spacing is possible to achieve a better upstream
transmission performance.
Q.T. Nguyen et al. [4] demonstrated Error-free transmission over 20km of 8-channels
for both downstream and upstream in colourless WDM-PON based on injection-locked
Fabry-Perot laser experimentally at 2.5Gbit/s, using a single quantum dash mode-locked
laser as multi-wavelength seeding source.
Hanlin Feny et al. [5] used a scheme in which modified NRZ format to realize multicast
WDM-PON by adjusting downstream extinction ratio and achieved good BER rate
performance for upstream signals.
Jun-Ichi Kani et al. [6] discussed the key role of WDM technologies in realizing the
next generation scalable and flexible PONs. That is one was WDM-PON in which each
ONU used different wavelength i.e a unique wavelength in each direction to communicate
with OLT and it also combined WDM and TDM technology.
Han et al. [7] proposed a WDM-PON model with multicast capability like high
scalability multi-wavelength converter and single copy broadcast capability by employing
multistage AWGs at remote node. The result of this architecture was evaluated in terms of
cost, scalability, link capacity and bandwidth per user in both upstream and downstream
signals. In this architecture, the existing passive star coupler was replaced by a special
passive optical device.
Gerd Keiser et al. [8] proposed and demonstrated a method for simultaneous real-time
status monitoring and troubleshooting of a high-capacity single-fiber bidirectional passive
optical network (PON) that is based on WDM techniques. To avoid interference between the
bidirectional traffic, downstream and upstream signals were assigned in different spectral
bands. The two main parts of the monitoring and fault-diagnosis functions were a traffic-
directing and amplification module and a signal-selection switch module. Using an optical
time-domain reflectometer, the fault-diagnosis test path can be greater than 50 km. Tests
results were presented for 10-Gb/s upstream and downstream links over 35-km distances.
Zhixin Liu et al. [9] proposed and demonstrated an optical multicast overlay scheme
on a wavelength-division-multiplexed passive optical network, employing bandwidth
efficient inverse return-to-zero duobinary signals. Multicast control was realized by tuning
the voltage bias at the point-to-point downstream modulator at the optical line terminal. The
10Gb/s downstream operation of the proposed optical multicast overlay scheme and 2.5-Gb/s
carrier distributed upstream transmission had been experimentally demonstrated.

222
DFB
Laser
Array
WDM
Multi-
plexer
Circu-
lators
CSRZ/DRZ
or MDRZ
Modulator
AWG
8*8
Circu-
lators
3R-
Regenerator
Low Pass Bessel
Filter
Q
measurement
BER Analyser
PIN
Detector
Optical
Transmitter
Power
Splitter
EDFA
AWG
1*8
Rajniti et al. [10] compared the performance of two modulation formats non return to
zero (NRZ), return to zero (RZ) for 2.5Gb/s bidirectional WDM/TDM-PON using narrowband
AWG. They investigated the impact of extinction ratio (ζ) of Mach-Zehnder (MZ) amplitude
modulator on the performance of WDM-PON for varying optical fiber lengths. The system
performance had been analyzed by varying the value of ζ from 2 to 22dB. They found that the
system gave optimum performance at extinction ratio (ζ) value 20dB. Further, the effect of
variation in the input power (from 0 to 20dBm) and transmission distance upto 60km was
observed in terms of Q value and eye opening for NRZ and RZ data formats. They found that
NRZ was superior to RZ and system gave optimum performance at input power Pin=10dBm.
In this paper, we have extended the work of reference [10], they compared the
performance of two modulation formats non return-to-zero (NRZ), return-to-zero (RZ) for
2.5Gb/s bidirectional WDM/TDM-PON using narrowband AWG. They evaluated the system
performance by varying input power (from 0 to 20dBm) and transmission distance up to 60km.
We have evaluated the system performance by using advanced modulation formats and
transmission distance upto 130km has been observed in terms of Q value and eye opening factor.
Here, in section 2, the system description and simulation parameters have been described. In
section 3, the results of the simulated system have been reported for different modulation data
formats, signal input power, bit rate and distance. Finally in section 4, conclusions are made.
II. SYSTEM DESCRIPTION AND SIMULATION
The Schematic of optical communication system simulation setup is shown in Fig.1. An
externally modulated CW DFB Laser Array having eight number of output ports, having
frequency of 1550nm, having channel spacing of 100GHz with variable input power (from 0 to
20dBm) is used. The WDM multiplexer also operates at the frequency of 1550nm with the
bandwidth 10GHz and channel spacing of 100Ghz.
Fig.1: Schematic of Simulation Setup

223
Three different types of modulation formats carrier suppressed return to zero (CSRZ),
duobinary return to zero (DRZ) and modified return to zero (MDRZ) has been used. An
Erbium Doped Fiber Amplifier with gain 17dB and noise figure 6dB is used in the transmitter
to boost the optical signal to the desired power level. The EDFA is followed by power splitter
and upstream circulator with return loss and isolation of 60dB Array waveguide grating
AWG (8×8) with frequency of 193.4THz and bandwidth 10GHz is used for upstream and
AWG(1×8) with frequency of 1550 nm and bandwidth of 10GHz is used for downstream. A
bidirectional Single Mode Fiber SMF fiber with parameters attenuation of 0.24dB/km,
dispersion slope of 0.075 ps/km-nm2
and dispersion at 1550nm is 16.75ps/km-nm has been
used and the length of fiber has been varied up to 130km.
III. RESULTS AND DISCUSSION
Three modulation formats have been compared by varying input power Pin (0-20dBm)
and transmission distance up to 130 km for 2.5×8Gb/s WDM-PON system in terms of Q
value [dB] and eye opening factor. To estimate the performance, the Q value [dB] and
maximum eye opening factor for the eye diagram of electrical scope have been considered for
channel 1 and channel 4. We have evaluated the system performance by varying bit rate at
2.5Gb/s, 5Gb/s and 10Gb/s and it is observed that the system gives optimal transmission
when the data is transmitted at the bit rate of 2.5Gb/s. The Fig. 2(a), 2(b) and 2(c) shows the
graphical representation of Q value as a function of signal input power for CSRZ, DRZ and
MDRZ data formats for downstream data respectively.
0 2 4 6 8 10 12 14 16 18 20
0
20
40
60
80
100
120
140
160
Signal input power Pin(dBm)
Q.factor(dB)
2.5Gb/sCh1
2.5Gb/sCh4
5Gb/sCh1
5Gb/sCh4
10Gb/sCh1
10Gb/sCh4
Fig. 2(a) Pin (dBm) Vs Q factor(dB) for CSRZ data format at distance 20km
It can be seen that all the formats that as the signal input power increases from 0 to
15dBm, Q value increases after which it starts falling. From this it is observed that for low
powers the performance of WDM-PON system increases with the increase in input power.

224
0 2 4 6 8 10 12 14 16 18 20
0
20
40
60
80
100
120
Q.factor(dB)
2.5Gb/sCh1
2.5Gb/sCh4
5Gb/sCh1
5Gb/sCh4
10Gb/sCh1
10Gb/sCh4
Fig. 2(b) Pin (dBm) Vs Q factor(dB) for DRZ data format at distance 20km
0 2 4 6 8 10 12 14 16 18 20
0
20
40
60
80
100
120
140
Q.factor(dB)
2.5Gb/sCh1
2.5Gb/sCh4
5Gb/sCh1
5Gb/sCh4
10Gb/sCh1
10Gb/sCh4
Fig. 2(c) Pin (dBm) Vs Q factor(dB) for MDRZ data format at distance 20km
However, with increases in power, the wavelength tend to overlap each other causing
more dominance of non linear effects like Cross Phase Modulation (XPM) and Four Wave
Mixing (FWM) and thus reducing the Q value after 15dBm. It is also been observed that by using
variable bit rate the system gives best performance at bit rate 2.5Gb/s. The graph clearly shows
that end channels are more affected by inter-channel FWM and noise as compared to middle
channel.
The Fig. 3(a), 3(b) and 3(c) shows the graphical representation of Q value as a function of
transmission distance at varied input power and bit rate of 2.5Gb/s WDM-PON system for CSRZ,
DRZ and MDRZ data formats for downstream signals respectively. The graph shows that as the
distance increases Q value deteriorates due to FWM effect and ASE noise.
10 20 30 40 50 60 70 80 90
0
20
40
60
80
100
120
140
160
180
Length(kms)
Q.factor(dB)
Power = 10dBm & Bit rate = 2.5Gb/s
CSRZ
DRZ
MDRZ
Fig.3 (a) Length(km) Vs Q.factor(dB) for CSRZ, DRZ and MDRZ modulation formats at input
power Pin = 10dBm and bit rate = 2.5Gb/s

225
10 20 30 40 50 60 70 80 90 100 110
0
50
100
150
Length(kms)
Q.factor(dB)
CSRZ
DRZ
MDRZ
Fig.3(b) Length(km) Vs Q.factor(dB) for CSRZ, DRZ and MDRZ modulation formats at input
It can also be seen from the graphs that for the input power Pin=10dBm and transmission
distance more than 90km, the Q value drops below the minimum required value of 6dB for
CSRZ, DRZ and MDRZ formats, due to ASE noise of EDFA’s. When bit rate for WDM-PON
system is 2.5Gb/s, the CSRZ gives better performance as compared to DRZ and MDRZ
modulation data formats.
0 20 40 60 80 100 120 140
0
10
20
30
40
50
60
Length(kms)
Q.factor(dB)
CSRZ
DRZ
MDRZ
Fig.3(c) Length(km) Vs Q.factor(dB) for CSRZ, DRZ and MDRZ modulation formats at input
Fig. 4(a) Eye Diagram at Pin=15dbm for CSRZ data format at distance 40km

226
Figure 4(a), 4(b) and 4(c) shows the eye diagrams for downstream data respectively
for CSRZ, DRZ and MDRZ modulation formats at distance 40km. These results further
endorse the results of earlier discussion. The results obtained are also consistent with the
results reported in [2].
Fig. 4(b) Eye Diagram at Pin=15dbm for DRZ data format at distance 40km
Fig. 4(c) Eye Diagram at Pin=15dbm for MDRZ data format at distance 40km
Similarly, Figure 5 shows the optical spectrums for CSRZ, DRZ and MDRZ
modulation formats with input power Pin=15dBm and at the distance of 40km having bit rate
of 2.5Gb/s. These results further endorse the results of earlier discussion.

227
(a) (b)
(c)
Fig. 5 Showing optical spectrum with Pin=15dbm at distance 40km having bit rate of 2.5Gb/s
for different modulation formats (a) CSRZ (b) DRZ (c) MDRZ
No further increase in system performance could be observed after input power Pin=
20dB.The best Q value obtained is 217.63dB and 190.85dB at Pin=15dBm and Pin=10dBm at
bit rate of 2.5Gb/s for CSRZ data format respectively.
IV. CONCLUSION
We have simulated 2.5×8Gb/s bi-directional WDM-PON system by varying input
power Pin, bit rate and transmission distance. It has been observed that as the signal input
power increases, Q value also increase up to 15dBm after which it starts decreasing due inter-
channel interference and non linear effects such as Cross Phase Modulation (XPM) and Four
Wave Mixing (FWM). Further, It is concluded that system gives better performance at bit
rate 2.5Gb/s for WDM-PON system as compared to 5Gb/s WDM-PON system. At bit rate
2.5Gb/s CSRZ gives better performance for WDM-PON system and at bit rate of 5Gb/s
MDRZ gives better performance as compared to other formats.

228
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