International Journal of Scientific & Engineering Research, Volume 5, Issue 6, June-2014 66
ISSN 2229-5518
Comparative Analysis of EDFA based 64 channel
WDM systems for different pumping techniques
Mishal Singla, Preeti, Sanjiv Kumar
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fluorescence, Erbium ions are efficiently used for
amplification in optical domain [6]. When an optical signal at
1550 nm wavelength enters the EDFA, the signal is combined
F OR the past two decades, Optical Fiber Communication
has been advanced rapidly as it is the process of achieving transmission bandwidth using optical waves as carrier. As the time goes for the further improvement of Optical Fiber Communication, need of coherent optical sources arises and lasers are developed [1]. But when a signal travels in an optical fibrevarious losses like attenuation, tap splice etc. occurs. In presence of such losses, it is difficult to detect the received signal. Therefore, for the long transmission, these losses have to be overcome in fibre using different means. One such mean is the use of fibre amplifier. Also, far before, the optical signals were converted to electrical signal then amplified and then reconverted to optical signal. But it was a complex and costly process. As the optical amplifiers are introduced, the conversion of signal to electrical signal is not required. So, optical amplifiers revolutionized the optical fibre communication field [3]. Optical amplifiers broadly are of two types: semiconductor amplifier and fibre amplifier. Fibre amplifiers are divided into Erbium Doped Fibre Amplifier (EDFA), Raman amplifier and Brillouin amplifier [4].
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• Preeti, Sanjiv Kumar are currently working as a assistant professor in electronics and communication department at University Institute of Engineering and Technology, Panjab University, India. E-mail: preeti_singh@pu.ac.in,sanjivsam86@gmail.com
For communication, there are practically two wavelength widows 1530nm to 1560nm(C-Band) and 1560nm to 1600nm (L-Band) [5]. EDFA can amplify a wide wavelength Range (1500nm - 1600nm) simultaneously , hence is very useful in wavelength division multiplexing for amplification. It is a
Conventional Silica fibre heavily doped with active
Erbium ions as the gain medium. Due to its property of
with a 980 nm or 1480nm pump laser through a wavelength division multiplexer device. The input signal and pump laser signal pass through fibre doped with Erbium ions .Erbium doped ions can be amplified the signal through the interaction at 1550nm [2]. EDFA is pumped in three ways: Co- Pumping, Counter pumping and Bidirectional Pumping. The performance of EDFA based WDM System depends on [7]:
1. Length of Erbium Doped Fibre
2. Pump Power
The performance analysis of a WDM (Wavelength Division
Multiplexing) system employed for long haul transmission is carried out in terms of Bit Error Rate (BER), Noise Figure and received Power [8]. In this paper, different techniques of pumping i.e. co-pumping, counter-pumping and bidirectional
pumping are analyzed for 64 channels in C- band [9] at 0.5 spacing for pump laser at 200mW at 980nm .
There are three basic sections of a WDM system i.e. transmitter, channel and the receiver. The transmitter section includes: 64 channel WDM transmitter, ideal multiplexer; communication channel includesideal isolator, Erbium Doped Fiber, Optical Fiber ; whereas Photodiode, low pass filter are a part of the receiver section[6]. BER analyzer and optical power meter are used to analyze the simulation results.
The system is designed in OptiSystem v7.0. In this, 64 channel
WDM signals are given at the input in the range of 1530nm-
1562nm having frequency spacing of 0.5nm at 10Gbps. The
input power of -26dBm is given to the channels. Doped ions
are excited to the higher energy level, when they pumped at
980nm.To prevent the effect of Amplified Spontaneous
Emission(ASE), isolator is used at the input end which also
prevent the propagation of the signal in backward direction.
Otherwise, population inversion is reduced due to
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International Journal of Scientific & Engineering Research, Volume 5, Issue 6, June-2014 67
ISSN 2229-5518
reflectedASE. Also,in EDFA, reflections of the output re-enter, and to overcomethis, isolatoris used at the output [7]. In this paper, three pumping techniques are compared i.e. Co- pumping, Counter pumping and Bidirectional pumping.
In Co-Pumping, the signals i.e input and pump, travel in the same direction in the fiber. These signals are combined using a pump co-coupler or wavelength division multiplexer. Inside the fiber, pump energy is given to signal at the input and amplified signal is received at the amplifier’s output. In this design, for the propagation of the signal in one direction, isolators are used.
In Counter Pumping, both the signals i.e input and pump, travel in opposite direction to each other in the fiber. For amplification the direction of input and pump signal is not essential. They can travel in any direction.
In Bi-directional, both the signals i.e input and pump, propagate in one direction. But in the fiber, two pump signals travel. One pump signal propagate in the same direction as the input signal and the other pump signal propagate in the direction opposite to that of signal at the input.
Figure1: Block Diagram of three pumping techniques (a) Co-Pumping (b) Counter- Pumping (c) Bidirectional Pumping
Optimization of different parameters is needed to be done so that system performance does not degrade too low. The parameters which are to be considered are pump power, length of EDFA and length of optical fiber. Input Power is taken to be -26dBm. Length of EDFA is varied from 4m to 10m [4]. Length of optical fiber is taken to be 25km andoptimized power of the pump is200mW at
980nm wavelength. Length of the Erbium Doped Fiber is increased and corresponding received power is recorded for different pumping techniques as shown in table1, table2, table3, table4.
TABLE1
POWER WITH THE VARYING LENGTH OF EDFA FOR CO-PUMPING TECHNIQUE
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International Journal of Scientific & Engineering Research, Volume 5, Issue 6, June-2014 68
ISSN 2229-5518
EDFA length. For higher length of EDFA bidirectional pumping and co-pumping will give better results. Comparing the table 1, table 2 and table 3 it can be concluded that the bidirectional pumping gives the maximum output power with EDFA length of 10m.
TABLE2
POWER WITH THE VARYING LENGTH OF EDFA FOR COUNTER-
PUMPING TECHNIQUE
TABLE 4
BER ANALYSIS FOR DIFFERENT PUMPING TECHNIQUES FOR EDFA
LENGTH OF 4M TO 10M
TABLE3
POWER WITH THE VARYING LENGTH OF EDFA FOR BIDIRECTIONAL -
PUMPING TECHNIQUE
Length of EDFA ( m) | Input power(E- 6) | Input Power (In dBm) | Output Power(E-3) | Output Power (In dBm) |
4 | 87.891 | -10.561 | 113.020 | 20.532 |
6 | 87.891 | -10.561 | 112.943 | 20.529 |
8 | 87.891 | -10.561 | 110.198 | 20.422 |
10 | 87.891 | -10.561 | 107.335 | 20.307 |
In the bidirectional pumping, power of each pump laser is maintained to be 100mW i.e. 100mW through co-coupler and
100mW through counter- coupler but total power for pumping is
maintained to be 200mW for EDFA It can be observed from table
1, table 2 and table 3 that with the increase in length of EDFA the
received power increase. Also it can be seen from table 2 that for
counter pumping the transmission is acceptable up to 8m of
From table 4, it can be observed that variation in BER of counter pumping is more than the variation in co-pumping and bidirectional pumping. So for 64 channels counter pumping is not preferred. Further, simulation results show that BER for co- pumping lies in e-20 to e-22, for counter-pumping lies in e-17 to e-21 and for bidirectional pumping lies in e-20 to e-22.
Similarly, the performance can be visualized from eye diagrams given in figure 4.
(a)
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International Journal of Scientific & Engineering Research, Volume 5, Issue 6, June-2014 69
ISSN 2229-5518
(b)
(c)
Figure 4: Eye diagram for (a) Co-pumping (b) Counter pumping (c)
Bidirectional pumping
Figure 5: Q-factor Analysis for different pumping techniques
1.
Q-factor (Quality Factor) for different pumping techniques lies between 8.5 to 9.7 and BER between e-17 to e-22.
Further, from the above results, received power in case of co- pump is less for higher length of EDFA (6m-10m). After considering all the factors, bidirectional pumping for 64 channels is optimized to have the received power of about 20dBm.
Comparative analysis of three pumping techniquesis given in this paper i.e co-pumping, counter pumping and bidirectional in terms of BER(Bit error rate) and Q-factor for different length of EDFA( 4m to 10m) in C-Band at input power of -26dBm and pump power of 200mW at 980nm pump wavelength. In case of co-pumping, received power decreases with increase in length of EDFA and BER lies in e-20 to e-22. For counter pumping, received power increases with increase in length and BER lies in e-17 to e-21, but transmission is acceptable up to 8m EDFA length. For bidirectional pumping, power decreases but provides more power as compare to other configurations and BER between e-20 to e-21 for 100mW pump lasers. So, for longer length of EDFA (8m-10m), bidirectional pumping will provide better and optimized results.
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