Gain Flattening of DWDM Channels for the Entire C & L Bands. Выравнивание усиления в каналах DWDM в полных полосах С и L
УДК 681.7.068 GAIN FLATTENING OF DWDM CHANNELS FOR THE ENTIRE C & L BANDS
© 2012 г.
S. M. Bilal, PhD Scholar; M. Zafrullah, PhD; M.K. Islam, PhD University of Engineering & Technology, Taxila – 47050, Pakistan. E-mail: syed.bilal@uettaxila.edu.pk, dr.zafrullah@uettaxila.edu.pk, drmk.islam@uettaxila.edu.pk
A hybrid amplifier consisting of one stage of Erbium Doped Fiber Amplifier and two stages of Raman amplifiers is constructed. Two Raman fibers are cascaded in series to suppress the intensity noise due to double Rayleigh scattering. Backward pumping is applied at all stages in order to increase the gain of Erbium Doped Fiber Amplifier and to decrease the polarization dependent gain of Raman fiber amplifier. In our previous experiment a 16 channel Wavelength Division Multiplexed system with channel spacing of 5 nanometers was considered. In this experiment a Density Wavelength Division Multiplexed system having 80 channels and a channel spacing of 0.8 nm was taken in to account. Gain Flattening is achieved for the entire C-band and L-bands. Experimental results showed that the hybrid amplifier has the average Gain of more than 19 dB in the wavelength range between 1530–1600 nanometers, with the Noise Figure of less than 6 decibels. The Gain of the Erbium Doped Fiber Amplifier and Raman was optimized to minimize the ripple value as low as 0.045 decibels with an output power of 15.265 decibelmilli.
Keywords: Raman fiber amplifier, hybrid amplifier, Erbium Doped Fiber Amplifier, Noise Figure, Wavelength Division multiplexing, Density Wavelength Division multiplexing, Gain Flattening Filter.
Codes OCIS: 060.0060, 060.2320.
Received 14.12.2011.
ВЫРАВНИВАНИЕ УСИЛЕНИЯ В КАНАЛАХ DWDM В ПОЛНЫХ ПОЛОСАХ С И L
© 2012 г. S. M. Bilal; M. Zafrullah; M. K. Islam
University of Engineering & Technology, Taxila, Pakistan
Разработан гибридный усилитель, состоящий из одного каскада эрбиевого волоконного усиления и двух рамановских усилительных каскадов. Два рамановских волоконных усилителя размещены последовательно для подавления шумов вследствие двойного рэлеевского рассеяния. Во всех усилителях направление волн накачки противоположно направлению распространения сигнала с целью увеличения усиления эрбиевым усилителем и снижения поляризационной зависимости усиления в рамановских каскадах. В наших предшествовавших экспериментах рассматривалась 16-канальная система с мультиплексированием по длине волны, со спектральным разносом каналов 5 нм. В настоящем эксперименте описана DWDM-система, содержащая 80 каналов с разносом каналов 0,8 нм. Выравнивание усиления достигнуто для полных С и L полос. Экспериментальные результаты показали, что гибридный усилитель обладает усилением более 19 дБ в полосе длин волн 1530–1600 нм, с шумовым показателем менее 6 Дб. Усиление в эрбиевом и рамановских усилителях было оптимизировано таким образом, чтобы уменьшить его неравномерность до 0,045 дБ при выходной мощности 15,265 дБм.
Ключевые слова: рамановский волоконный усилитель, гибридный усилитель, эрбиевый волоконный усилитель, коэффициент шума, система с мультиплексированием по длине волны, плотные WDM, фильтр, выравнивающий усиление.
1. Introduction
Different techniques exist to enhance the flattened gain bandwidth of fiber amplifiers such as using gain equalizers (GEQ’s), new host materi-
als and connecting Erbium Doped Fiber Amplifier (EDFA) and thulium – doped fiber amplifiers in parallel configuration [1–4]. The techniques also include an EDFA, a GEQ and an Raman Fiber Amplifier (RFA) in serial configuration [5].
40 “Оптический журнал”, 79, 9, 2012
One possible way to increase the Gain Bandwidth is to combine numerous amplifiers with different Bandwidth Gain’s and construct a hybrid amplifier [6]. These amplifiers could either be connected in series or parallel configuration. In parallel configuration Wavelength Division Multiplexed (WDM) signals that serve as an input to the amplifiers are demultiplexed by the WDM coupler into numerous wavelength band groups. After amplification, these signals are again multiplexed through a WDM coupler [7]. On the contrary a very wide seamless Gain Band is observed for the amplifiers joined together in series configuration, because they do not need any WDM couplers. So connecting an EDFA amplifier in series with an RFA is an effectual approach because RFA can give any gain band by appropriately choosing the pump wavelengths and powers.
Thus, in order to add spectral shaping flexibility in broadband applications a high output power EDFA can be used with RFA [8]. The main bottleneck in such configuration lies in correctly setting up pump wavelengths and pump powers for RFA’s. Optimization of the pump wavelength and pump power can make the gain spectrum extremely flat [9]. However Raman amplifiers are modeled by non-linear coupled equations with pump-pump and pump-signal interactions and there is no simple relation between wavelength, gain and power of the multiple pump lasers that can be found without seriously compromising the accuracy of the results [10].
In our previous work [11] the gain of EDFA and Raman amplifiers was optimized for long haul WDM systems. In this work the simulation setup is same as in [11] but the results were obtained for an 80 channel Density Wavelenght division multiplexed (DWDM) system. Fig. 1
shows the setup, used for the purpose of simulation which is the same as used in [11]. The difference is that, instead of a WDM transmitter and receiver a DWDM transmitter and receiver is used. Pump powers and pump wavelengths for laser diodes are same as used in [11]. But in order to compensate 80 channels and to obtain a flat gain, the parameters of the transmission filter also known as the Gain Flattening Filter (GFF) are changed, optimized and adjusted.
The fundamentals of hybrid amplifiers and several important results are given in [12–24].
2. Simulation Setup and Results
The simulation setup, shown in fig. 1, consists of an 80 channel DWDM transmitter with each channel carrying a 10 Gbps signal with a power of –20 dBm per channel in the wavelength range of 1530–1600 nm with 0.8 nm spacing. DWDM channels served as an input to the 5 m EDFA pumped by a laser diode. A laser array of 8 laser diodes act as an input to the first stage of 25 km Raman fiber where second stage of Raman fiber is pumped by a single laser diode [11]. By using the technique of accurate numerical methods, optimized values of pump power and pump wavelengths for the laser diodes were found [11]. These values are the same as used in [11] and are given in fig. 2–5, and table.
Simulation results for the gain of each stage and noise figure were obtained by using the mathematical equations of Gain and Noise Figure given in [11] (fig. 6–8).
A thin film 2 port Gain Equalization Filter or Gain Flattening Filter (GFF) with the operating wavelength range in the C/L band is used for the purpose of Gain Equalization [11]. The filter used in this experiment is the same Dynamic
MUX Wavelength Selective Coupler MUX Wavelength Selective Coupler Wavelength Selective Coupler
DEMUX
DWDM Transmitter
EDFA Pump
Isolator
RAMAN Fiber 1
Pump
Isolator
RAMAN Fiber 2
Pump
GFF
DWDM Reciever
Pump Laser 1
Fig. 1. Simulation Setup.
“Оптический журнал”, 79, 9, 2012
Pump Array
Pump Laser 2
41
Power (dBm)
20
0
–20
–40
–60
–80
–100 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 2. Power in dBm after passing through EDFA.
Power (dBm)
10 0 –10
–20
–30
–40 –50
–60 –70
–80
–90 –100
1520
1530 1540 1550 1560 1570 1580 1590 1600 Wavelength (nm)
1610
Fig. 5. Power in dBm after passing through Gain Flattening Filter.
Power (dBm)
20
0
–20
–40
–60
–80 –100
1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 3. Power in dBm after passing through first Raman fiber.
20
0
–20
–40 –60
–80
–100 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 4. Power in dBm after passing through 2nd Raman fiber.
Gain (dB)
26 24 22 20 18
16 14 12 10
8 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 6. Gain Profile after passing through EDFA.
Pump powers and wavelengths for the laser diodes after applying the optimization
Pump Sources Wavelength, nm
Power, mW
Pump Laser 1
1458.91
91.2012
Pump Array (8 pumps)
1430.599; 1437.846; 46.78; 48.52; 1444.967; 1454.552; 43.04; 66.85; 1465.354; 1482.255; 154.76; 191.90;
1493.366; 1510 173.04; 187.67
Pump Laser 2
1503.24
209.887
Gain Flattening Filter (DGFF) continuous envelope equalizer [11] but instead of using 16 independent notches [11], 24 notches were used. By using this filter, although overall gain of the system has reduced to 19 dB but astonishing results were obtained for the ripple factor. The ripple factor was reduced to as low as 0.045 dB in comparison with 0.7 dB obtained in [11].
Power (dBm)
42 “Оптический журнал”, 79, 9, 2012
Gain (dB)
31 30 29 28 27 26 25 24 23 22 21 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 7. Gain Profile after passing through first Raman fiber.
27
26
25
24
23
22
21
20
19 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 8. Gain Profile after passing through 2nd Raman fiber.
NF (dB)
Gain (dB)
19,78 19,77 19,76
Hybrid Amplifier Gain
19,75
19,74
19,73
19,72 1530 1540 1550 1560 1570 1580 1590 1600 Wavelength (nm)
Fig. 9. Gain Profile after passing through Gain Flattening Filter.
5,8
5,6
5,4
5,2
5,0
4,8
4,6
4,4
4,2 1530
1540
1550 1560
1570
Wavelength (nm)
Fig. 10. Noise Figure.
Hybrid Amplifier NF 1580 1590 1600
Gain (dB)
Gain profile shown in Fig. 9, indicates a maxi- nel DWDM system is considered. The optimized
mum Gain of 19.775 dB and a minimum Gain pump powers and pump wavelengths for the laser
of 19.73 dB. So the ripple value which is calcu- diodes are the same as in the previous experiment
lated as Gmax – Gmin comes out to be 0.045 dB. The maximum value of Noise Figure (NF) was
but in order to obtain a flat gain for 80 channel system, parameters of GFF were changed and op-
observed to be 5.4 dB, as can be seen in Fig. 10: timized. Gain Flattening is achieved for the en-
Noise Figure and total Power was found to be tire C band and L band. We obtain a high gain
15.265 dBm.
in the wavelength range from 1530–1600 nm
by using hybrid amplifiers. Simulation results
3. Conclusion
show that the ripple values can be minimized to as low as 0.045 dB. Optimized values for the
We have constructed a hybrid amplifier com- wavelengths and powers of pump sources were
prising of one stage of Erbium Doped Fiber Am- obtained by accurate numerical methods. Gain
plifier (EDFA) and two stages of Raman amplifi- Equalization is achieved with the help of a Gain
ers. Two Raman fibers are cascaded in series to Flattening Filter (GFF). Thus a hybrid amplifier
suppress the intensity noise due to double Ray- with an average Gain of 19 dB, an output power
leigh scattering. In our previous experiment, of 15.265 dBm, a ripple value less than 0.05 dB,
optimized results were obtained for a 16 channel and a NF less than 6 dB in the 70-nm gain band
WDM system. In this experiment an 80 chan- was achieved.
* * * * *
“Оптический журнал”, 79, 9, 2012
43
REFERENCES
1. Masuda H., Kawai S. Wide band and Gain-flattened hybrid fiber amplifier consisting of an EDFA and multiwavelength pumped RAMAN amplifier / / IEEE Photonics Technology Letters. 1999. V. 11. № 6. P. 647–649.
2. Yamada M., Mori A., Kobayashi K., Ono H., Kanamori T., Nishida Y., Ohishi Y. Low noise and gain-flattened Er3+-doped tellurite fiber amplifier // Tech. Dig. Optical Amplifiers and Their Applications OAA. 1998. P. 103–106, paper TuC2.
3. Wysocki P.F., Juskins J.B., Espindola R.P., Andrejco M., Vengasarkar A.M. Broad-band erbium-doped fiber amplifier flattened beyond 40 nm using long-period grating filter // IEEE Photonics Technology Letters. 1997. V. 9. № 10. P. 1343–1345.
4. Sun Y., Sulhoff J.W., Srivastava A.K., Abramov A., Strasser T.A., Wysocki P.F., Pedrazzani J.R., Judkins J.B., Espindola R.P., Wolf C., Zyskind J.L., Vengsarkar A.M., Zhou J. A gain-flattened ultra wide band EDFA for high capacity WDM optical communications systems // Tech. Dig. European Conference on Optical Communication. ECOC 1. 1998. P. 53–54.
5. Kawai S., Masuda H., Suzuki K.-I., Aida K. Ultrawide, 75-nm 3-dB gain-band optical amplifier utilizing gainflattened erbium-doped fluoride fiber amplifier and discrete Raman amplification // Electronics Letters. 1998. V. 34. № 9. P. 897–898.
6. Kawai S., Masuda H., Suzuki K.-I., Aida K. Wide-Bandwidth and Long-Distance WDM Transmission Using Highly Gain-Flattened Hybrid Amplifier // IEEE Photonics Technology Letters. 1999. V. 11. № 7. P. 886–888.
7. Sakamoto T., Aozasa S-I., Yamada M., Shimizu M. Hybrid amplifiers consisting of EDFA and TDFA for WDM signals // Journal of Lightwave Technology. 2006. V. 24. № 6. P. 2287.
8. Karasek M., Menif M., Bellemare A. Design of Wideband Hybrid Amplifiers for Local Area Networks // IEE Proc. Optoelectronic. 2001. V. 148. № 3. P. 150–155.
9. Martini M.M.J., Castellani C.E.S., Pontes M.J., Ribeiro M.R.N., Kalinowski H.J Gain Profile Optimization for Raman+EDFA Hybrid Amplifiers with Recycled Pumps for WDM Systems // Journal of Microwaves, Optoelectronics and Electromagnetic Applications. 2010. V. 9. № 2. P. 100–112.
10. Castellani C.E.S., Cani S.P.N., Segatto M.E.V., Pontes M.J., Romero M.A. Design methodology for multi-pumped discrete RAMAN amplifiers:case study employing photonic crystal fibers // Optic Express. 2009. V. 17. № 16. P. 14121–14131.
11. Bilal S.M., Zafrullah M., Islam M.K. Achieving Gain Flattening With Enhanced Bandwidth for Long Haul WDM Systems // Journal of Optical Technology (JOT). 2012. V. 79. № 2.
12. Liaw S.-K., Ho K.-P., Huang C.-K., Chen W.-T., Hsiao Y.-L. Investigate C+L band EDFA/Raman amplifiers by using the same pump lasers // 6th International Joint Conference on Information and Computing (JCIS2006). JCIS2006 Kaohsoung Taiwan. paper PNC-11.
13. SunY., Srivastava A.K., Zhou J., Sulhoff J.W. Optical fiber amplifiers for WDM optical networks // Bell Labs Technical Journal. 1999. V. 4. № 1. P. 187–206.
14. Islam M.N. Raman Amplifiers for Telecommunications // Journals of Selected Topics in Quantum Electronics. 2002. V. 8. № 3. P. 548–559.
15. Hwang S., Song K.-W., Song K.-U., Park S-H., Nilsson J., Cho K. Comparitive high power conversion efficiency of C-plus L-band EDFA // Electronics Letters. 2001. V. 37. № 25. P. 1539–1541.
16. Agrawal G.P. Fiber-Optic Communication Systems // 3rd Edition. John Wiley and Sons, USA. 2002.
17. Becker P.C., Olsson N.A., Simpson J.R. Erbium-doped fiber amplifiers funda mentals and technology // Academic Press, 1999. P. 47.
18. Agrawal G.P. Nonlinear Fiber Optics. 2nd Edition. Academic press, New York. 1995.
19. Carena A., Curri V., Poggiolini P. On the Optimization of Hybrid Raman/Erbium-Doped Fiber Amplifiers // IEEE Photonics Technology Letters. 2001. V. 13. № 11. P. 1170–1172.
20. Tiwari U., Thyagarajan K., Shenoy M.R. Simulation and Experimental Characterization of Raman/EDFA Hybrid Amplifier with Enhanced Performance // Optics Communications, ELSEVIER. 2009. V. 82. № 8. P. 1563–1566.
21. Martini M.M.J., Castellani C.E.S., Pontes M.J., Ribeiro M.R.N., Kalinowski H.1. Multipump Optimization for RAMAN+EDFA hybrid amplifiers under pump residual recycling // SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference. IMOC. 2009. P. 117–121.
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22. Hansen P.B., Eskildsen L., Stentz A.J., Strasser T.A., Judkins J., DeMarco J.J., Pedrazzani R., DiGiovanni D.J. Rayleigh scattering limitations in distributed Raman pre-amplifiers // IEEE Photonics Technology Letters. 1998. V. 10. № 1. P. 159–161.
23. Emori Y., Kado S., Namiki S. Broadband flat-gain and low-noise Raman amplifiers pumped by wavelengthmultiplexed high power laser diodes // Optical Fiber Technology. 2002. V. 8. № 2. P. 107–122.
24. Yan M., Chen J., Jiang W., Li J., Chen J., Li X. Automatic design scheme for optical fiber Raman amplifiers backward pumped with multiple laser diode pumps // IEEE Photonics Technology Letters. 2001. V. 13. № 9. P. 948–950.
“Оптический журнал”, 79, 9, 2012
45
© 2012 г.
S. M. Bilal, PhD Scholar; M. Zafrullah, PhD; M.K. Islam, PhD University of Engineering & Technology, Taxila – 47050, Pakistan. E-mail: syed.bilal@uettaxila.edu.pk, dr.zafrullah@uettaxila.edu.pk, drmk.islam@uettaxila.edu.pk
A hybrid amplifier consisting of one stage of Erbium Doped Fiber Amplifier and two stages of Raman amplifiers is constructed. Two Raman fibers are cascaded in series to suppress the intensity noise due to double Rayleigh scattering. Backward pumping is applied at all stages in order to increase the gain of Erbium Doped Fiber Amplifier and to decrease the polarization dependent gain of Raman fiber amplifier. In our previous experiment a 16 channel Wavelength Division Multiplexed system with channel spacing of 5 nanometers was considered. In this experiment a Density Wavelength Division Multiplexed system having 80 channels and a channel spacing of 0.8 nm was taken in to account. Gain Flattening is achieved for the entire C-band and L-bands. Experimental results showed that the hybrid amplifier has the average Gain of more than 19 dB in the wavelength range between 1530–1600 nanometers, with the Noise Figure of less than 6 decibels. The Gain of the Erbium Doped Fiber Amplifier and Raman was optimized to minimize the ripple value as low as 0.045 decibels with an output power of 15.265 decibelmilli.
Keywords: Raman fiber amplifier, hybrid amplifier, Erbium Doped Fiber Amplifier, Noise Figure, Wavelength Division multiplexing, Density Wavelength Division multiplexing, Gain Flattening Filter.
Codes OCIS: 060.0060, 060.2320.
Received 14.12.2011.
ВЫРАВНИВАНИЕ УСИЛЕНИЯ В КАНАЛАХ DWDM В ПОЛНЫХ ПОЛОСАХ С И L
© 2012 г. S. M. Bilal; M. Zafrullah; M. K. Islam
University of Engineering & Technology, Taxila, Pakistan
Разработан гибридный усилитель, состоящий из одного каскада эрбиевого волоконного усиления и двух рамановских усилительных каскадов. Два рамановских волоконных усилителя размещены последовательно для подавления шумов вследствие двойного рэлеевского рассеяния. Во всех усилителях направление волн накачки противоположно направлению распространения сигнала с целью увеличения усиления эрбиевым усилителем и снижения поляризационной зависимости усиления в рамановских каскадах. В наших предшествовавших экспериментах рассматривалась 16-канальная система с мультиплексированием по длине волны, со спектральным разносом каналов 5 нм. В настоящем эксперименте описана DWDM-система, содержащая 80 каналов с разносом каналов 0,8 нм. Выравнивание усиления достигнуто для полных С и L полос. Экспериментальные результаты показали, что гибридный усилитель обладает усилением более 19 дБ в полосе длин волн 1530–1600 нм, с шумовым показателем менее 6 Дб. Усиление в эрбиевом и рамановских усилителях было оптимизировано таким образом, чтобы уменьшить его неравномерность до 0,045 дБ при выходной мощности 15,265 дБм.
Ключевые слова: рамановский волоконный усилитель, гибридный усилитель, эрбиевый волоконный усилитель, коэффициент шума, система с мультиплексированием по длине волны, плотные WDM, фильтр, выравнивающий усиление.
1. Introduction
Different techniques exist to enhance the flattened gain bandwidth of fiber amplifiers such as using gain equalizers (GEQ’s), new host materi-
als and connecting Erbium Doped Fiber Amplifier (EDFA) and thulium – doped fiber amplifiers in parallel configuration [1–4]. The techniques also include an EDFA, a GEQ and an Raman Fiber Amplifier (RFA) in serial configuration [5].
40 “Оптический журнал”, 79, 9, 2012
One possible way to increase the Gain Bandwidth is to combine numerous amplifiers with different Bandwidth Gain’s and construct a hybrid amplifier [6]. These amplifiers could either be connected in series or parallel configuration. In parallel configuration Wavelength Division Multiplexed (WDM) signals that serve as an input to the amplifiers are demultiplexed by the WDM coupler into numerous wavelength band groups. After amplification, these signals are again multiplexed through a WDM coupler [7]. On the contrary a very wide seamless Gain Band is observed for the amplifiers joined together in series configuration, because they do not need any WDM couplers. So connecting an EDFA amplifier in series with an RFA is an effectual approach because RFA can give any gain band by appropriately choosing the pump wavelengths and powers.
Thus, in order to add spectral shaping flexibility in broadband applications a high output power EDFA can be used with RFA [8]. The main bottleneck in such configuration lies in correctly setting up pump wavelengths and pump powers for RFA’s. Optimization of the pump wavelength and pump power can make the gain spectrum extremely flat [9]. However Raman amplifiers are modeled by non-linear coupled equations with pump-pump and pump-signal interactions and there is no simple relation between wavelength, gain and power of the multiple pump lasers that can be found without seriously compromising the accuracy of the results [10].
In our previous work [11] the gain of EDFA and Raman amplifiers was optimized for long haul WDM systems. In this work the simulation setup is same as in [11] but the results were obtained for an 80 channel Density Wavelenght division multiplexed (DWDM) system. Fig. 1
shows the setup, used for the purpose of simulation which is the same as used in [11]. The difference is that, instead of a WDM transmitter and receiver a DWDM transmitter and receiver is used. Pump powers and pump wavelengths for laser diodes are same as used in [11]. But in order to compensate 80 channels and to obtain a flat gain, the parameters of the transmission filter also known as the Gain Flattening Filter (GFF) are changed, optimized and adjusted.
The fundamentals of hybrid amplifiers and several important results are given in [12–24].
2. Simulation Setup and Results
The simulation setup, shown in fig. 1, consists of an 80 channel DWDM transmitter with each channel carrying a 10 Gbps signal with a power of –20 dBm per channel in the wavelength range of 1530–1600 nm with 0.8 nm spacing. DWDM channels served as an input to the 5 m EDFA pumped by a laser diode. A laser array of 8 laser diodes act as an input to the first stage of 25 km Raman fiber where second stage of Raman fiber is pumped by a single laser diode [11]. By using the technique of accurate numerical methods, optimized values of pump power and pump wavelengths for the laser diodes were found [11]. These values are the same as used in [11] and are given in fig. 2–5, and table.
Simulation results for the gain of each stage and noise figure were obtained by using the mathematical equations of Gain and Noise Figure given in [11] (fig. 6–8).
A thin film 2 port Gain Equalization Filter or Gain Flattening Filter (GFF) with the operating wavelength range in the C/L band is used for the purpose of Gain Equalization [11]. The filter used in this experiment is the same Dynamic
MUX Wavelength Selective Coupler MUX Wavelength Selective Coupler Wavelength Selective Coupler
DEMUX
DWDM Transmitter
EDFA Pump
Isolator
RAMAN Fiber 1
Pump
Isolator
RAMAN Fiber 2
Pump
GFF
DWDM Reciever
Pump Laser 1
Fig. 1. Simulation Setup.
“Оптический журнал”, 79, 9, 2012
Pump Array
Pump Laser 2
41
Power (dBm)
20
0
–20
–40
–60
–80
–100 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 2. Power in dBm after passing through EDFA.
Power (dBm)
10 0 –10
–20
–30
–40 –50
–60 –70
–80
–90 –100
1520
1530 1540 1550 1560 1570 1580 1590 1600 Wavelength (nm)
1610
Fig. 5. Power in dBm after passing through Gain Flattening Filter.
Power (dBm)
20
0
–20
–40
–60
–80 –100
1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 3. Power in dBm after passing through first Raman fiber.
20
0
–20
–40 –60
–80
–100 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 Wavelength (nm)
Fig. 4. Power in dBm after passing through 2nd Raman fiber.
Gain (dB)
26 24 22 20 18
16 14 12 10
8 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 6. Gain Profile after passing through EDFA.
Pump powers and wavelengths for the laser diodes after applying the optimization
Pump Sources Wavelength, nm
Power, mW
Pump Laser 1
1458.91
91.2012
Pump Array (8 pumps)
1430.599; 1437.846; 46.78; 48.52; 1444.967; 1454.552; 43.04; 66.85; 1465.354; 1482.255; 154.76; 191.90;
1493.366; 1510 173.04; 187.67
Pump Laser 2
1503.24
209.887
Gain Flattening Filter (DGFF) continuous envelope equalizer [11] but instead of using 16 independent notches [11], 24 notches were used. By using this filter, although overall gain of the system has reduced to 19 dB but astonishing results were obtained for the ripple factor. The ripple factor was reduced to as low as 0.045 dB in comparison with 0.7 dB obtained in [11].
Power (dBm)
42 “Оптический журнал”, 79, 9, 2012
Gain (dB)
31 30 29 28 27 26 25 24 23 22 21 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 7. Gain Profile after passing through first Raman fiber.
27
26
25
24
23
22
21
20
19 1530 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Fig. 8. Gain Profile after passing through 2nd Raman fiber.
NF (dB)
Gain (dB)
19,78 19,77 19,76
Hybrid Amplifier Gain
19,75
19,74
19,73
19,72 1530 1540 1550 1560 1570 1580 1590 1600 Wavelength (nm)
Fig. 9. Gain Profile after passing through Gain Flattening Filter.
5,8
5,6
5,4
5,2
5,0
4,8
4,6
4,4
4,2 1530
1540
1550 1560
1570
Wavelength (nm)
Fig. 10. Noise Figure.
Hybrid Amplifier NF 1580 1590 1600
Gain (dB)
Gain profile shown in Fig. 9, indicates a maxi- nel DWDM system is considered. The optimized
mum Gain of 19.775 dB and a minimum Gain pump powers and pump wavelengths for the laser
of 19.73 dB. So the ripple value which is calcu- diodes are the same as in the previous experiment
lated as Gmax – Gmin comes out to be 0.045 dB. The maximum value of Noise Figure (NF) was
but in order to obtain a flat gain for 80 channel system, parameters of GFF were changed and op-
observed to be 5.4 dB, as can be seen in Fig. 10: timized. Gain Flattening is achieved for the en-
Noise Figure and total Power was found to be tire C band and L band. We obtain a high gain
15.265 dBm.
in the wavelength range from 1530–1600 nm
by using hybrid amplifiers. Simulation results
3. Conclusion
show that the ripple values can be minimized to as low as 0.045 dB. Optimized values for the
We have constructed a hybrid amplifier com- wavelengths and powers of pump sources were
prising of one stage of Erbium Doped Fiber Am- obtained by accurate numerical methods. Gain
plifier (EDFA) and two stages of Raman amplifi- Equalization is achieved with the help of a Gain
ers. Two Raman fibers are cascaded in series to Flattening Filter (GFF). Thus a hybrid amplifier
suppress the intensity noise due to double Ray- with an average Gain of 19 dB, an output power
leigh scattering. In our previous experiment, of 15.265 dBm, a ripple value less than 0.05 dB,
optimized results were obtained for a 16 channel and a NF less than 6 dB in the 70-nm gain band
WDM system. In this experiment an 80 chan- was achieved.
* * * * *
“Оптический журнал”, 79, 9, 2012
43
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