- Email: [email protected]
Experimental study on tandem pumped fiber amplifier
Optics & Laser Technology 44 (2012) 1570–1573
Contents lists available at SciVerse ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Experimental study on tandem pumped fiber amplifier Hu Xiao, Jiangming Xu, Wuming Wu, Pu Zhou n, Xiaojun Xu College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2011 Received in revised form 29 November 2011 Accepted 29 November 2011 Available online 4 January 2012
We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%. Crown Copyright & 2011 Published by Elsevier Ltd. All rights reserved.
Keywords: Tandem pump Fiber amplifier Doubles clad fiber
1. Introduction The research on ytterbium-doped fiber lasers (YDFLs) has been intense for their outstanding characteristics, such as high efficiency and power handling ability. With the development of highpower laser diode (LD) sources and advances in double-clad fiber (DCF) design and fabrication, kilowatt-level YDFLs pumped by 975 nm LDs have been successfully achieved already [1–7]. Nevertheless, the brightness of LDs, thermal loads, nonlinearities and optical damage of the fiber have severely hindered the higher power scaling [8] of YDFLs. For the low brightness of the 975 nm LDs, the pump power is difficult to be coupled into the gain fiber efficiently. And for a 975 nm pumped YDFL, the quantum defect is about 10%, which would produce heavy thermal load inside the gain fiber at high power level and may lead to the damage of fiber. Shkurikin [9] of IPG photonics has predicted that, the output power of YDFL would be limited at kilowatt level by the low brightness of LDs and the thermal load, considering the current state of art in the design and manufacturing of LD and fiber. The key for achieving much higher power YDFLs lies in the brightness enhancement of high power LDs and the efficient thermal management of the fiber. Tandem pumping, in which one or several fiber lasers pump another one, has been considered to be an ideal scheme for higher power scaling [7,10]. By means of rather simple and robust configuration, one can achieve a 3–4 orders brightness enhancement of the fiber laser’s beam compared to that of the diode laser [2,10,11]. For its high brightness, the output of fiber lasers can be efficiently launched into a gain fiber with low loss to provide adequate pump power. Tandem
n
Corresponding author. E-mail address: [email protected] (P. Zhou).
pumping also makes it possible to pump close to the emission wavelength so that the quantum defect heating can be low, resulting in a reduced thermal load [8]. For example, IPG’s 10 kW fiber laser is pumped by YDFLs at 1018 nm and emitted at 1070 nm [7], corresponding to a quantum defect of less than 5% in the final gain stage, which is nearly half of that when directly pumped by 975 nm LDs. Thus the thermal load in gain fiber can be effectively relieved. Tandem pumping is also demonstrated to be helpful to control the excessive excitation and gain and thus improve the beam quality of output laser by Codemard et al. [12]. Wirth et al. [13] have reported a high power tandem pumped fiber amplifier with an output power of 2.9 kW, but not in allfiber configuration. In this paper, we demonstrate an all-fiberized 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The 1030 nm laser is launched into a length of home-made double-clad YDF via combiner and high power wave division multiplexer (WDM) to pump a 1083 nm signal laser. Output properties with two pump schemes are experimentally investigated. The 1083 nm signal laser is amplified to 2.4 W with power conversion efficiency of 60% when the gain fiber is 22 m long.
2. Experiment 2.1. Experimental setup The 1030 nm and 1083 nm seed laser used in our experiment have the same resonant cavity structure depicted in Fig. 1, except that the optical components are of different wavelengths. A 50:50 wide-band fiber coupler is used in the resonant cavity. By splicing the two output ports together, we can attain a reflectivity as high as 99.5%. The FBG’s reflectivity is 50% at center wavelength and is
0030-3992/$ - see front matter Crown Copyright & 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2011.11.047
H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
become stronger with longer gain fiber and thus intensify the amplified spontaneous emission (ASE), which in turn would suppress the amplification of the 1030 nm laser. Meanwhile, the actual center wavelength of our pump sources is 972 nm, at which the absorption is 1.5 dB lower than that at 975 nm [8]. Shown in Fig. 4 is the spectrum distribution of the amplifier measured at its maximum output power level. There is no residual pump power among the output light and indicates the good performance of our pump striper. It is observed in Fig. 4 that the ASE has built up in longer wavelength region but still 20 dB weaker than the 1030 nm laser. We have attempted the cladding-pump scheme at first. The 1030 nm laser is launched into the gain fiber via the combiner. The 1030 nm laser propagates in the inner cladding of the gain fiber while the 1083 nm signal laser in the core. The measured
6
1030 nm laser power (W)
used as output coupler. The gain fiber is Nufern SM-YSF-HI and has a length of 0.5 m. The 975 nm pump light is launched into gain fiber through a single mode WDM. The experimental setup is depicted in Fig. 2. The 1030 nm seed laser is preamplified to about 150 mW and then seeded to the power scaling amplifier. The pump sources of this stage are two 975 nm pigtailed LDs, the output of which are launched into the inner cladding of 4 m double-clad YDF purchased from Nufern. A pump stripper is used in this stage to get rid of the residual diode laser. The gain fiber has a 5/130 mm core/inner cladding size with 0.12/0.46 NA. Its nominal absorption coefficient is 1.7 dB/m at 975 nm. The gain fiber used for tandem pumping is homemade DCF, which has a 11 mm core and 130 mm inner cladding with a step-index profile. The NA of the core and inner cladding are 0.075 and 0.46, respectively. The cladding absorption coefficient is about 5 dB/m at 975 nm. The 1030 and 1083 nm laser can be launched into the gain fiber either via a high power WDM or combiner. The WDM has two pigtailed input ports, which are corresponding to 1030 and 1083 nm laser, respectively. The output port of the WDM employs a length of double clad Ge-doped fiber, matched with the gain fiber. The output fiber of the combiner has the same parameters as that of the WDM. Both the 1030 and 1083 nm laser are launched into the core of the gain fiber if the WDM is used, while the 1030 nm laser travels in the inner cladding when the combiner is employed. The gain fiber’s output end is 81 angle cleaved to suppress parasitic oscillation. Isolators (ISO) are used between amplification stages to prevent backward light.
1571
amplifier output WDM output
5 4 3 2 1 0
0
5
2.2. Experimental results
20
Fig. 3. Output power of 1030 nm power scaling amplifier versus pump power.
LD
-30 Relative Intensity /dB
Fig. 3 shows the output power of the 1030 nm power scaling amplifier as a function of pump power. The output power after the WDM is also depicted. The insertion loss (IL) of the WDM is calculated to be 0.58 dB. The power conversion efficiency of the power scaling amplifier is less than 30%, which is much lower than the usual level of 70–80% [14]. This is caused by the insufficient gain fiber length and its low absorption coefficient at 975 nm. Increasing the gain fiber length would certainly enhance the pump absorption, but not improve the power conversion efficiency effectively. The gain near 1040 nm would
10 15 Pump power (W)
-40 -50 -60 -70 -80 950
Coupler
FBG
WDM
1100
Fig. 4. Spectrum of the 1030 nm power scaling amplifier.
LD laser
1050
Wavelength /nm
Output
Fig. 1. Schematic diagram of the seed laser.
1030 nm seed
1000
Nufren DCF
Preamp ISO
Pump stripper
Combiner
DCF
Power scaling LD
ISO
WDM or
amplifier
1083 nm seed
combiner
Preamp
ISO
laser Fig. 2. Experimental setup of tandem pumping fiber amplifier.
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H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
output spectrum (Fig. 5) when pump power is 1 W indicates that the pump laser cannot be absorbed adequately, and the signal laser is rarely amplified. In the core-pump experiment, the 1030 nm pump laser and the 1083 nm signal laser are both launched into the core of the gain fiber through the WDM. The output properties of the tandem pumped amplifier are plotted in Fig. 6. The maximum output powers with three different gain fiber lengths are 1.5 W, 1.9 W and 2.4 W, when the gain fibers are 41 m, 33 m and 22 m, respectively. The spectrum of the amplifier at the maximum output power of 2.4 W is plotted in Fig. 7, with a resolution of 0.5 nm. The residual 1030 nm laser still exists in the spectrum but
Relative Intensity /dB
-40 -50 -60 -70 -80 -90 1000
1050
1100
1150
it is 20 dB lower than the 1083 nm signal laser and can be neglected. The maximum power conversion efficiency of our tandem-pumped amplifier is only 60%, out of accord with the high-efficiency characteristic of tandem pumping. This is due to the excessive absorption loss of the signal laser. To ensure the sufficient absorption of the 1030 nm laser, the gain fiber should be long enough. Nevertheless, the absorption at 1083 nm would also increase, which in turn degrades the power conversion efficiency of the amplifier. That corresponds with our experimental results in which the output power varies inversely with the gain fiber length. It is to be noted that in our core-pump scheme, though DCF is employed as the gain fiber, the pump power is launched into the core of DCF via WDM. That indicates that the maximum output power of our core-pumped amplifier is greatly limited by the power the WDM could handle. For high power scaling, combiners are more capable. In our experiment, the cladding-pump scheme fails due to the small pump power fill factor. If the core size of the gain fiber could be increased to 20 mm, then the pump power fill factor would be about 3 times increased. Thus the absorption at 1030 nm rises to 4 times as it is now, which could be appropriate for the use of cladding-tandem pump. Increasing the core size would also make it possible to use shorter gain fiber, which means lower absorption loss of the signal laser and higher nonlinear thresholds. Nevertheless, large core size also means the degradation of the beam quality. There should be a compromise between them.
Wavelength /nm Fig. 5. Spectrum of the cladding pumped fiber amplifier.
In conclusion, we have presented the detailed characteristics of a tandem pumped amplifier in all-fiber configuration. Both the cladding-pump and core-pump schemes are attempted for tandem pumping. The 1083 nm signal laser can hardly be amplified when cladding pumped by 1030 nm fiber laser for the low power fill factor and absorption coefficient at 1030 nm. With the corepump scheme, the 1083 nm signal laser can be amplified effectively. The maximum output power of the amplifier is measured to be 1.5 W, 1.9 W and 2.4 W with the gain fiber lengths of 41 m, 33 m and 22 m, respectively. The maximum power conversion efficiency is 60%. Employing gain fiber with larger core size is analyzed to be an appropriate approach for cladding-pump scheme.
1083 nm laser power (W)
2.5
22 m 33 m 41 m
2
1.5 1
0.5
0
0
1
2 3 1030 nm laser power (W)
4
References
Fig. 6. 1083 nm output power versus pump power with different gain fiber lengths.
Relative Intensity /dB
0 -20 -40 -60 -80 1000
3. Conclusion
1050 1100 Wavelength /nm
1150
Fig. 7. Spectrum of the tandem pumped fiber amplifier.
[1] Jeong Y, Sahu JK, Payne DN, Nilsson J. Ytterbium-doped large-core fibre laser with 1 kW of continuous-wave output power. Electronics Letters 2004;40: 470–2. [2] Jeong Y, Sahu JK, Payne DN. Ytterbium-doped large-core fiber laser with 1.36 kW continuous-wave output power. Optics Express 2004;12:6088–92. [3] /http://www.ipgphotonics.comS. [4] /http://www.nufern.com/kilowatt-amp.phpS. [5] Gapontsev V, Gapontsev D, Platonov N, Shkurikhin O, Fomin V, Mashkin A, et al. 2 kW CW ytterbium fiber laser with record diffraction-limited brightness. In: Proceedings of the European conference on lasers and electro-optics, paper CJ-11-THU; 2005. [6] Horley R, Norman S, Zervas MN. Progress and development in fibre laser technology. Proceedings of the SPIE 2007;6738:K7380–6. [7] Stiles E. New developments in IPG fiber laser technology. In: Proceedings of the fifth international workshop on fiber lasers; 2009. [8] Richardson DJ, Nilsson J, Clarkson WA. High power fiber lasers: current status and future perspectives. Journal of the Optical Society of America B 2010;27: B63–91. [9] /http://www.laserfocusworld.com.cn/Detc.asp?id=25S. [10] Minelly JD, Laming RI, Townsend JE, Barnes WL, Taylor ER, Jedrzejewski KP, et al. High-gain fibre power amplifier tandem-pumped by a 3 W multi-stripe diode. In: Proceedings of the optical fiber communications conference. Optical Society of America; 1992. p. 32–3.
H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
[11] Jeong Y, Boyland AJ, Sahu JK, Chung S, Nilsson J, Payne DN. Multi-kilowatt single-mode ytterbium-doped large-core fiber laser. Journal of the Optical Society of Korea 2009;13:416–22. [12] Codemard CA, Sahu JK, Nilsson J. Tandem cladding-pumping for control of excess gain in ytterbium-doped fiber amplifiers. IEEE Journal of Quantum Electronics 2010;46:1860–9.
1573
¨ [13] Wirth C, Schmidt O, Kliner A, Schreiber T, Eberhardt R, Tunnermann A. High power tandem pumped amplifier with an output power of 2.9 kW. Optics Letters 2011;36:3061–3. ¨ [14] Limpert J, Roser F, Klingebiel S, Schreiber T, Wirth C, Peschel T, et al. The rising power of fiber lasers and amplifiers. IEEE Journal of Selected Topics in Quantum Electronics 2007;13:537–45.
Contents lists available at SciVerse ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Experimental study on tandem pumped fiber amplifier Hu Xiao, Jiangming Xu, Wuming Wu, Pu Zhou n, Xiaojun Xu College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2011 Received in revised form 29 November 2011 Accepted 29 November 2011 Available online 4 January 2012
We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%. Crown Copyright & 2011 Published by Elsevier Ltd. All rights reserved.
Keywords: Tandem pump Fiber amplifier Doubles clad fiber
1. Introduction The research on ytterbium-doped fiber lasers (YDFLs) has been intense for their outstanding characteristics, such as high efficiency and power handling ability. With the development of highpower laser diode (LD) sources and advances in double-clad fiber (DCF) design and fabrication, kilowatt-level YDFLs pumped by 975 nm LDs have been successfully achieved already [1–7]. Nevertheless, the brightness of LDs, thermal loads, nonlinearities and optical damage of the fiber have severely hindered the higher power scaling [8] of YDFLs. For the low brightness of the 975 nm LDs, the pump power is difficult to be coupled into the gain fiber efficiently. And for a 975 nm pumped YDFL, the quantum defect is about 10%, which would produce heavy thermal load inside the gain fiber at high power level and may lead to the damage of fiber. Shkurikin [9] of IPG photonics has predicted that, the output power of YDFL would be limited at kilowatt level by the low brightness of LDs and the thermal load, considering the current state of art in the design and manufacturing of LD and fiber. The key for achieving much higher power YDFLs lies in the brightness enhancement of high power LDs and the efficient thermal management of the fiber. Tandem pumping, in which one or several fiber lasers pump another one, has been considered to be an ideal scheme for higher power scaling [7,10]. By means of rather simple and robust configuration, one can achieve a 3–4 orders brightness enhancement of the fiber laser’s beam compared to that of the diode laser [2,10,11]. For its high brightness, the output of fiber lasers can be efficiently launched into a gain fiber with low loss to provide adequate pump power. Tandem
n
Corresponding author. E-mail address: [email protected] (P. Zhou).
pumping also makes it possible to pump close to the emission wavelength so that the quantum defect heating can be low, resulting in a reduced thermal load [8]. For example, IPG’s 10 kW fiber laser is pumped by YDFLs at 1018 nm and emitted at 1070 nm [7], corresponding to a quantum defect of less than 5% in the final gain stage, which is nearly half of that when directly pumped by 975 nm LDs. Thus the thermal load in gain fiber can be effectively relieved. Tandem pumping is also demonstrated to be helpful to control the excessive excitation and gain and thus improve the beam quality of output laser by Codemard et al. [12]. Wirth et al. [13] have reported a high power tandem pumped fiber amplifier with an output power of 2.9 kW, but not in allfiber configuration. In this paper, we demonstrate an all-fiberized 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The 1030 nm laser is launched into a length of home-made double-clad YDF via combiner and high power wave division multiplexer (WDM) to pump a 1083 nm signal laser. Output properties with two pump schemes are experimentally investigated. The 1083 nm signal laser is amplified to 2.4 W with power conversion efficiency of 60% when the gain fiber is 22 m long.
2. Experiment 2.1. Experimental setup The 1030 nm and 1083 nm seed laser used in our experiment have the same resonant cavity structure depicted in Fig. 1, except that the optical components are of different wavelengths. A 50:50 wide-band fiber coupler is used in the resonant cavity. By splicing the two output ports together, we can attain a reflectivity as high as 99.5%. The FBG’s reflectivity is 50% at center wavelength and is
0030-3992/$ - see front matter Crown Copyright & 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2011.11.047
H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
become stronger with longer gain fiber and thus intensify the amplified spontaneous emission (ASE), which in turn would suppress the amplification of the 1030 nm laser. Meanwhile, the actual center wavelength of our pump sources is 972 nm, at which the absorption is 1.5 dB lower than that at 975 nm [8]. Shown in Fig. 4 is the spectrum distribution of the amplifier measured at its maximum output power level. There is no residual pump power among the output light and indicates the good performance of our pump striper. It is observed in Fig. 4 that the ASE has built up in longer wavelength region but still 20 dB weaker than the 1030 nm laser. We have attempted the cladding-pump scheme at first. The 1030 nm laser is launched into the gain fiber via the combiner. The 1030 nm laser propagates in the inner cladding of the gain fiber while the 1083 nm signal laser in the core. The measured
6
1030 nm laser power (W)
used as output coupler. The gain fiber is Nufern SM-YSF-HI and has a length of 0.5 m. The 975 nm pump light is launched into gain fiber through a single mode WDM. The experimental setup is depicted in Fig. 2. The 1030 nm seed laser is preamplified to about 150 mW and then seeded to the power scaling amplifier. The pump sources of this stage are two 975 nm pigtailed LDs, the output of which are launched into the inner cladding of 4 m double-clad YDF purchased from Nufern. A pump stripper is used in this stage to get rid of the residual diode laser. The gain fiber has a 5/130 mm core/inner cladding size with 0.12/0.46 NA. Its nominal absorption coefficient is 1.7 dB/m at 975 nm. The gain fiber used for tandem pumping is homemade DCF, which has a 11 mm core and 130 mm inner cladding with a step-index profile. The NA of the core and inner cladding are 0.075 and 0.46, respectively. The cladding absorption coefficient is about 5 dB/m at 975 nm. The 1030 and 1083 nm laser can be launched into the gain fiber either via a high power WDM or combiner. The WDM has two pigtailed input ports, which are corresponding to 1030 and 1083 nm laser, respectively. The output port of the WDM employs a length of double clad Ge-doped fiber, matched with the gain fiber. The output fiber of the combiner has the same parameters as that of the WDM. Both the 1030 and 1083 nm laser are launched into the core of the gain fiber if the WDM is used, while the 1030 nm laser travels in the inner cladding when the combiner is employed. The gain fiber’s output end is 81 angle cleaved to suppress parasitic oscillation. Isolators (ISO) are used between amplification stages to prevent backward light.
1571
amplifier output WDM output
5 4 3 2 1 0
0
5
2.2. Experimental results
20
Fig. 3. Output power of 1030 nm power scaling amplifier versus pump power.
LD
-30 Relative Intensity /dB
Fig. 3 shows the output power of the 1030 nm power scaling amplifier as a function of pump power. The output power after the WDM is also depicted. The insertion loss (IL) of the WDM is calculated to be 0.58 dB. The power conversion efficiency of the power scaling amplifier is less than 30%, which is much lower than the usual level of 70–80% [14]. This is caused by the insufficient gain fiber length and its low absorption coefficient at 975 nm. Increasing the gain fiber length would certainly enhance the pump absorption, but not improve the power conversion efficiency effectively. The gain near 1040 nm would
10 15 Pump power (W)
-40 -50 -60 -70 -80 950
Coupler
FBG
WDM
1100
Fig. 4. Spectrum of the 1030 nm power scaling amplifier.
LD laser
1050
Wavelength /nm
Output
Fig. 1. Schematic diagram of the seed laser.
1030 nm seed
1000
Nufren DCF
Preamp ISO
Pump stripper
Combiner
DCF
Power scaling LD
ISO
WDM or
amplifier
1083 nm seed
combiner
Preamp
ISO
laser Fig. 2. Experimental setup of tandem pumping fiber amplifier.
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H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
output spectrum (Fig. 5) when pump power is 1 W indicates that the pump laser cannot be absorbed adequately, and the signal laser is rarely amplified. In the core-pump experiment, the 1030 nm pump laser and the 1083 nm signal laser are both launched into the core of the gain fiber through the WDM. The output properties of the tandem pumped amplifier are plotted in Fig. 6. The maximum output powers with three different gain fiber lengths are 1.5 W, 1.9 W and 2.4 W, when the gain fibers are 41 m, 33 m and 22 m, respectively. The spectrum of the amplifier at the maximum output power of 2.4 W is plotted in Fig. 7, with a resolution of 0.5 nm. The residual 1030 nm laser still exists in the spectrum but
Relative Intensity /dB
-40 -50 -60 -70 -80 -90 1000
1050
1100
1150
it is 20 dB lower than the 1083 nm signal laser and can be neglected. The maximum power conversion efficiency of our tandem-pumped amplifier is only 60%, out of accord with the high-efficiency characteristic of tandem pumping. This is due to the excessive absorption loss of the signal laser. To ensure the sufficient absorption of the 1030 nm laser, the gain fiber should be long enough. Nevertheless, the absorption at 1083 nm would also increase, which in turn degrades the power conversion efficiency of the amplifier. That corresponds with our experimental results in which the output power varies inversely with the gain fiber length. It is to be noted that in our core-pump scheme, though DCF is employed as the gain fiber, the pump power is launched into the core of DCF via WDM. That indicates that the maximum output power of our core-pumped amplifier is greatly limited by the power the WDM could handle. For high power scaling, combiners are more capable. In our experiment, the cladding-pump scheme fails due to the small pump power fill factor. If the core size of the gain fiber could be increased to 20 mm, then the pump power fill factor would be about 3 times increased. Thus the absorption at 1030 nm rises to 4 times as it is now, which could be appropriate for the use of cladding-tandem pump. Increasing the core size would also make it possible to use shorter gain fiber, which means lower absorption loss of the signal laser and higher nonlinear thresholds. Nevertheless, large core size also means the degradation of the beam quality. There should be a compromise between them.
Wavelength /nm Fig. 5. Spectrum of the cladding pumped fiber amplifier.
In conclusion, we have presented the detailed characteristics of a tandem pumped amplifier in all-fiber configuration. Both the cladding-pump and core-pump schemes are attempted for tandem pumping. The 1083 nm signal laser can hardly be amplified when cladding pumped by 1030 nm fiber laser for the low power fill factor and absorption coefficient at 1030 nm. With the corepump scheme, the 1083 nm signal laser can be amplified effectively. The maximum output power of the amplifier is measured to be 1.5 W, 1.9 W and 2.4 W with the gain fiber lengths of 41 m, 33 m and 22 m, respectively. The maximum power conversion efficiency is 60%. Employing gain fiber with larger core size is analyzed to be an appropriate approach for cladding-pump scheme.
1083 nm laser power (W)
2.5
22 m 33 m 41 m
2
1.5 1
0.5
0
0
1
2 3 1030 nm laser power (W)
4
References
Fig. 6. 1083 nm output power versus pump power with different gain fiber lengths.
Relative Intensity /dB
0 -20 -40 -60 -80 1000
3. Conclusion
1050 1100 Wavelength /nm
1150
Fig. 7. Spectrum of the tandem pumped fiber amplifier.
[1] Jeong Y, Sahu JK, Payne DN, Nilsson J. Ytterbium-doped large-core fibre laser with 1 kW of continuous-wave output power. Electronics Letters 2004;40: 470–2. [2] Jeong Y, Sahu JK, Payne DN. Ytterbium-doped large-core fiber laser with 1.36 kW continuous-wave output power. Optics Express 2004;12:6088–92. [3] /http://www.ipgphotonics.comS. [4] /http://www.nufern.com/kilowatt-amp.phpS. [5] Gapontsev V, Gapontsev D, Platonov N, Shkurikhin O, Fomin V, Mashkin A, et al. 2 kW CW ytterbium fiber laser with record diffraction-limited brightness. In: Proceedings of the European conference on lasers and electro-optics, paper CJ-11-THU; 2005. [6] Horley R, Norman S, Zervas MN. Progress and development in fibre laser technology. Proceedings of the SPIE 2007;6738:K7380–6. [7] Stiles E. New developments in IPG fiber laser technology. In: Proceedings of the fifth international workshop on fiber lasers; 2009. [8] Richardson DJ, Nilsson J, Clarkson WA. High power fiber lasers: current status and future perspectives. Journal of the Optical Society of America B 2010;27: B63–91. [9] /http://www.laserfocusworld.com.cn/Detc.asp?id=25S. [10] Minelly JD, Laming RI, Townsend JE, Barnes WL, Taylor ER, Jedrzejewski KP, et al. High-gain fibre power amplifier tandem-pumped by a 3 W multi-stripe diode. In: Proceedings of the optical fiber communications conference. Optical Society of America; 1992. p. 32–3.
H. Xiao et al. / Optics & Laser Technology 44 (2012) 1570–1573
[11] Jeong Y, Boyland AJ, Sahu JK, Chung S, Nilsson J, Payne DN. Multi-kilowatt single-mode ytterbium-doped large-core fiber laser. Journal of the Optical Society of Korea 2009;13:416–22. [12] Codemard CA, Sahu JK, Nilsson J. Tandem cladding-pumping for control of excess gain in ytterbium-doped fiber amplifiers. IEEE Journal of Quantum Electronics 2010;46:1860–9.
1573
¨ [13] Wirth C, Schmidt O, Kliner A, Schreiber T, Eberhardt R, Tunnermann A. High power tandem pumped amplifier with an output power of 2.9 kW. Optics Letters 2011;36:3061–3. ¨ [14] Limpert J, Roser F, Klingebiel S, Schreiber T, Wirth C, Peschel T, et al. The rising power of fiber lasers and amplifiers. IEEE Journal of Selected Topics in Quantum Electronics 2007;13:537–45.