OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 19 — Sep. 23, 2013
  • pp: 21847–21856
« Show journal navigation

Frequency resolved transverse mode instability in rod fiber amplifiers

Mette Marie Johansen, Marko Laurila, Martin D. Maack, Danny Noordegraaf, Christian Jakobsen, Thomas Tanggaard Alkeskjold, and Jesper Lægsgaard  »View Author Affiliations


Optics Express, Vol. 21, Issue 19, pp. 21847-21856 (2013)
http://dx.doi.org/10.1364/OE.21.021847


View Full Text Article

Acrobat PDF (11075 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Frequency dynamics of transverse mode instabilities (TMIs) are investigated by testing three 285/100 rod fibers in a single-pass amplifier setup reaching up to ~200W of extracted output power without beam instabilities. The pump power is increased well above the TMI threshold to uncover output dynamics, and allowing a simple method for determining TMI threshold based on standard deviation. The TMI frequency component is seen to appear on top of system noise that may trigger the onset. A decay of TMI threshold with test number is identified, but the threshold is fully recovered between testing to the level of the pristine fiber by thermal annealing the fiber output end to 300°C for 2 h.

© 2013 OSA

1. Introduction

Ytterbium-doped silica based fiber lasers and amplifiers currently undergo significant improvements concerning beam quality performance and extractable average and peak power [1

1. D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B 27(11), B63–B92 (2010). [CrossRef]

]. High pulse energies and peak powers require large effective area and new fiber designs are being investigated [2

2. T. T. Alkeskjold, M. Laurila, L. Scolari, and J. Broeng, “Single-mode ytterbium-doped large-mode-area photonic bandgap rod fiber amplifier,” Opt. Express 19(8), 7398–7409 (2011). [CrossRef] [PubMed]

5

5. F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, “The influence of index-depressions in core-pumped Yb-doped large pitch fibers,” Opt. Express 18(26), 26834–26842 (2010). [CrossRef] [PubMed]

]. As state of the art large mode area (LMA) fiber amplifier can extract 100s of Watts per unit length, thermal-optic effects causing a thermally induced refractive index increment significantly influences the waveguiding mechanisms [6

6. D. C. Brown and H. J. Hoffman, “Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers,” IEEE J. Quantum Electron. 37(2), 207–217 (2001). [CrossRef]

8

8. J. Limpert, T. Schreiber, A. Liem, S. Nolte, H. Zellmer, T. Peschel, V. Guyenot, and A. Tünnermann, “Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation,” Opt. Express 11(22), 2982–2990 (2003). [CrossRef] [PubMed]

]. The index perturbations can cause very LMA fibers to support higher order modes (HOMs) at high power operation which can lead to mode degradation, and eventually transverse mode instability (TMI) that sets in at a threshold power level [9

9. A. V. Smith and J. J. Smith, “Mode instability in high power fiber amplifiers,” Opt. Express 19(11), 10180–10192 (2011). [CrossRef] [PubMed]

11

11. B. Ward, C. Robin, and I. Dajani, “Origin of thermal modal instabilities in large mode area fiber amplifiers,” Opt. Express 20(10), 11407–11422 (2012). [CrossRef] [PubMed]

]. The temporal characteristics of TMIs reveal rapid fluctuating beam output on the ms time scale, where the fundamental mode (FM) and the first HOM interact [12

12. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express 20(14), 15710–15722 (2012). [CrossRef] [PubMed]

]. FM and HOM interactions significantly degrade the beam quality, where the initially Gaussian like mode profile starts to fluctuate as TMIs set in. TMIs are often the first nonlinear effect to set in for very LMA fibers in high power amplifier and laser systems, and appear when the extracted average output power reaches a certain threshold. Currently TMIs set the upper limit for power scaling, and understanding the origin and mechanisms behind are important for future mitigation strategies. TMI can be observed with a standard CCD camera, but typically the refresh rate is too low to resolve the temporal dynamics [12

12. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express 20(14), 15710–15722 (2012). [CrossRef] [PubMed]

,13

13. F. Stutzki, H.-J. Otto, F. Jansen, C. Gaida, C. Jauregui, J. Limpert, and A. Tünnermann, “High-speed modal decomposition of mode instabilities in high-power fiber lasers,” Opt. Lett. 36(23), 4572–4574 (2011). [CrossRef] [PubMed]

]. Thus quantifying the underlying output evolution is impossible, and measuring the exact TMI threshold becomes extremely challenging. A simple and cheap method to detect TMI formation and evolution is required to quantify origin and dynamics. Different numerical models have been used to understand and explain the origin of TMIs ranging from heavy beam propagation models [9

9. A. V. Smith and J. J. Smith, “Mode instability in high power fiber amplifiers,” Opt. Express 19(11), 10180–10192 (2011). [CrossRef] [PubMed]

,11

11. B. Ward, C. Robin, and I. Dajani, “Origin of thermal modal instabilities in large mode area fiber amplifiers,” Opt. Express 20(10), 11407–11422 (2012). [CrossRef] [PubMed]

,14

14. C. Jauregui, T. Eidam, J. Limpert, and A. Tünnermann, “The impact of modal interference on the beam quality of high-power fiber amplifiers,” Opt. Express 19(4), 3258–3271 (2011). [CrossRef] [PubMed]

] to simpler semi-analytic models [15

15. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett. 37(12), 2382–2384 (2012). [CrossRef] [PubMed]

18

18. L. Dong, “Stimulated thermal Rayleigh scattering in optical fibers,” Opt. Express 21(3), 2642–2656 (2013). [CrossRef] [PubMed]

]. However the models have dissimilarities indicating a need for thorough experimental investigations of TMI.

2. Experimental setup

A time trace of the pinholed beam is recorded for every ~3 W of increased extracted output power of the 2nd, 8th, and 15th TMI test of each TMI repeat with FUT1 (i.e. FUT1-A2, FUT1-A8, FUT1-A15, FUT1-C2, FUT1-C8, FUT1-C15). The time trace is Fourier transformed to attain a frequency spectrum corresponding to a specific signal power. All the spectra from one TMI test (e.g. FUT1-A2) are plotted together as a spectrogram showing the output spectra normalized to the maximum signal power of that test in dB as a function of extracted output power and frequency. The spectrograms reveal the frequency evolution with increased output power, and are compared with the measured standard deviation of the pinholed beam to define the onset of TMIs.

3. Transverse mode instability onset and dynamics

The spectrograms recorded for FUT1 are considered in this section and reveal the frequency evolution of the recorded output of the pinholed photodiode with increased pump. Figure 2
Fig. 2 Data for FUT1-A2. Fourier transformed normalized spectrogram plotted in dB for the extracted output power as a function of frequency. The standard deviation is plotted on equal power scale to the right.
shows the frequency spectrogram for extracted output power above 100 W of FUT1-A2. The standard deviation measured by the photodiode and oscilloscope is plotted on the same power scale on the right in Fig. 2. Up to 180 W of extracted output power, the DC component, which represents the FM signal, dominates the spectrum, and is visible in the spectrogram as the sharp line centered at 0 Hz. Above 180 W, TMI sets in having a clear frequency component of 360 Hz with also higher harmonics of that component at 720 Hz, 1080 Hz, and 1440 Hz. This is caused by beam fluctuations between the FM and first HOM, that are very obvious in the spectrogram and also visible by the CCD camera, but can be difficult to detect due to the camera’s slow refresh rate. The TMI frequency components become power dependant above the TMI threshold of 180 W, where the peaks drift to higher frequencies with increased signal power. Otto et al. [12

12. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express 20(14), 15710–15722 (2012). [CrossRef] [PubMed]

] have reported on temporal peak fluctuations, which could be related. We believe that the frequency drift is caused by continuous waveguide perturbations with increased output power due to the thermo-optic effect and possibly also temperature dependent material constants. At around 200 W, new frequency components enter the spectrogram also with visible higher harmonics, and morelines enter again at 220 W, where after the TMI spectrogram becomes more continuous in nature as a white light span of frequencies.

Closely spaced vertical lines are observed in the spectrogram that seem independent of output power and stays constant in frequency. These lines are spaced with 50 Hz and are speculated to originate from the European grid frequency. At 180 W, where the TMIs set in with frequency components of 360 Hz, 720 Hz, 1080 Hz, and 1440 Hz, it seems as the main TMI frequency appear on top of a suspected vertical “electrical noise line”. It is suspected that system dependent noise can work as a trigger for TMI, and thus the threshold level becomes noise dependent, which has also been demonstrated in numerical work [15

15. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett. 37(12), 2382–2384 (2012). [CrossRef] [PubMed]

,16

16. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Theoretical analysis of mode instability in high-power fiber amplifiers,” Opt. Express 21(2), 1944–1971 (2013). [CrossRef] [PubMed]

].

The standard deviation in Fig. 2 is approximately zero below 180 W of extracted output power identified as a stable regime. At 180 W the standard deviation grows abrupt when TMIs set in reaching the so called transient regime with discrete frequency components followed by the more chaotic regime characteristic of a continuous frequency output, which will become more apparent in the following spectrograms for FUT1. The TMI threshold is clearly defined at 180 W of extracted output power from the abrupt increase in standard deviation when comparing to the clear appearance of an extra discrete frequency peak in the spectrogram.

All three recorded spectrograms from TMI repeat 1, i.e. FUT1-A2, FUT1-A8, FUT1-A15, are plotted in Fig. 4
Fig. 4 Spectrogram for FUT1-A2, FUT1-A8, and FUT1-A15 plotted together for comparison.
on equal output power axis to allow for comparison. The output power level at which the first TMI frequency component appear is seen to drop with test number.

FUT1 is thermally annealed after 15 tests in TMI repeat 1 to remove color centers created under the tests: TMI anneal. The output end of the 281/100 rod fiber is heated to 300C for 2 h and slowly cooled down. A new set of tests is performed: TMI repeat 2.

The spectrogram and standard deviation for FUT1-C2 is plotted in Fig. 5
Fig. 5 Data for FUT1-C2. Fourier transformed normalized spectrogram plotted in dB for the extracted output power as a function of frequency. The standard deviation is plotted on equal power scale to the right.
similar to Fig. 2 and Fig. 3, that is test number 2 in TMI repeat 2. The first TMI generated frequency peak appears at 340 Hz at 187 W of signal power, which is 7 W higher than FUT1-A2 in Fig. 2. Again the second, third and fourth harmonics are visible at 680 Hz, 1020 Hz, and 1370 Hz in Fig. 5, and a similar drift in frequency with increased pump power is observed. The TMI regime changes from transient to chaotic at 231 W. The standard deviation grows when TMI components appear, however not as abruptly as observed in TMI repeat 1. The discrete frequency peaks are vague between ~220 W – 231 W, which is also reflected in the lower standard deviation recorded by the pinholed photodiode. At 231 W of output power the standard deviation instantly increases as the output enters the chaotic regime.

The three spectrograms from TMI repeat 2, i.e. FUT1-C2, FUT1-C8, FUT1-C15, are plotted together in Fig. 6
Fig. 6 Spectrogram for FUT1-C2, FUT1-C8, and FUT1-C15 plotted together for comparison.
on equal output power axis for comparison. Again the TMIfrequency components are observed to appear at lower output power with test number. Also the transition from the transient to chaotic regime occurs at decreasing output power.

The vertical noise lines are visible in all spectrograms especially three lines at 250 Hz, 300 Hz, and 350 Hz with a frequency spacing of 50 Hz. These are attributed to a progression of the European utility frequency of 50 Hz. The first TMI frequency peaks appear at 360 Hz, 390 Hz and 340 Hz in Fig. 2, 3, and 5, all close to a vertical noise line. One theory of TMIs by Hansen et al. [15

15. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett. 37(12), 2382–2384 (2012). [CrossRef] [PubMed]

] predicts that TMIs can be seeded by system noise instead of quantum noise, which means that the vertical noise lines in the spectrograms could initiate coupling between the FM and HOM by sideband modulation of the signal. In TMI repeat 2 the noise lines are amplified and appear more evident compared to TMI repeat 1.

4. Transverse mode instability threshold definition

The measured standard deviations increase as soon as TMI frequency components appear in the spectrograms in Fig. 4 and Fig. 6, and are plotted together in Fig. 7
Fig. 7 Standard deviation as a function of extracted output power for TMI repeat 1 (top) and TMI repeat 2 (bottom). TMI threshold is defined at the level where the standard deviation reaches 0.01 indicated by the dashed line.
. The increase seems to be rather abrupt and step like, and not exponential as observed by Otto et al. in [12

12. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express 20(14), 15710–15722 (2012). [CrossRef] [PubMed]

]. This leads to a simple definition of the TMI threshold as the output power level where the standard deviation becomes larger than 0.01 indicated by the dashed line in Fig. 7.

The average TMI threshold of TMI repeat 1 decreases from 180 W – 156 W over the first 10 tests, A1 – A10. The TMI threshold is recovered between TMI repeat 1 and TMI repeat 2 by the thermal annealing to an average value of 178 W in the first test of TMI repeat 2, C1, and decreases with test number to 161 W in test 10 of TMI repeat 2, C10. The difference between TMI threshold of A1 and C1 is 2 W, less than the estimated uncertainty of the power meter, thus the TMI threshold seems fully recovered by thermal annealing. The average TMI threshold also decays to approximately the equal output powers, 156 W and 161 W, after 10 tests in TMI repeat 1 and 2 confirming the trend of TMI threshold decay with test number.

The TMI frequency components appear roughly on top of the noise line at 350 Hz in the 6 spectrograms in Fig. 4 and Fig. 6, indicating that the noise level might influence the TMI threshold. Noise variations could lead to TMI threshold variations showing up as uncertainties in Fig. 8. Externally generated noise could also interfere momentarily with the measurement affecting the TMI threshold.

5. Conclusion

The properties of TMIs have been investigated by testing three 285/100 rod fibers in a single-pass amplifier setup reaching up to ~200 W of extracted output power without beam instabilities. The pump power was increased during testing well above the threshold for TMI to uncover TMI dynamics and to set a simple definition for TMI threshold. The fibers were tested in three steps: One TMI repeat consisting of minimum 10 tests performed on initially pristine fibers, followed by one thermal annealing step, TMI anneal, where the fibers were heated to 300C for 2 h to thermally recover the TMI threshold. Hereafter another TMI repeat was performed to investigate the TMI dynamics and threshold again. Three different regimes for the output were identified with increasing pump power. The stable regime, having an FM Gaussian-like output with a DC component centered at 0 Hz, is on average below ~180W. A second frequency was generated apart from the DC component, when TMIs set in as harmonic beam oscillations between the FM and first HOM at TMI threshold. Higher harmonic beam fluctuations of this frequency are observed with increasing output power as long as the fiber is operated in the transient regime. Further increase in output power changed the regime to chaotic, where the beam fluctuations consisted of a white continuum of frequencies. The TMI frequency components were observed to originate on top of system noise speculated to be electrical noise lines, and we believe that the electrical amplitude noise triggers the onset of TMI. A pinholed photodiode measured standard deviation, which was seen to increase abruptly in a step-wise manner at TMI onset. This led to the simple definition of TMI threshold at the output power where the standard deviation reached 0.01. The 285/100 rod fibers had a TMI threshold that decayed with the number of performed tests, but could be fully recovered by a thermal annealing step in the experimental procedure.

References and links

1.

D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B 27(11), B63–B92 (2010). [CrossRef]

2.

T. T. Alkeskjold, M. Laurila, L. Scolari, and J. Broeng, “Single-mode ytterbium-doped large-mode-area photonic bandgap rod fiber amplifier,” Opt. Express 19(8), 7398–7409 (2011). [CrossRef] [PubMed]

3.

M. Laurila, M. M. Jørgensen, K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Distributed mode filtering rod fiber amplifier delivering 292W with improved mode stability,” Opt. Express 20(5), 5742–5753 (2012). [CrossRef] [PubMed]

4.

C.-H. Liu, G. Chang, N. Litchinitser, D. Guertin, N. Jacobsen, K. Tankala, and A. Galvanauskas, “Chirally Coupled Core Fibers at 1550-nm and 1064-nm for Effectively Single-Mode Core Size Scaling,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest Series (CD) (Optical Society of America, 2007), paper CTuBB3.

5.

F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, “The influence of index-depressions in core-pumped Yb-doped large pitch fibers,” Opt. Express 18(26), 26834–26842 (2010). [CrossRef] [PubMed]

6.

D. C. Brown and H. J. Hoffman, “Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers,” IEEE J. Quantum Electron. 37(2), 207–217 (2001). [CrossRef]

7.

M.-A. Lapointe, S. Chatigny, M. Piché, M. Cain-Skaff, and J.-N. Maran, “Thermal effects in high power cw fiber lasers,” Proc. SPIE 7195, 71951U, 71951U-11 (2009). [CrossRef]

8.

J. Limpert, T. Schreiber, A. Liem, S. Nolte, H. Zellmer, T. Peschel, V. Guyenot, and A. Tünnermann, “Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation,” Opt. Express 11(22), 2982–2990 (2003). [CrossRef] [PubMed]

9.

A. V. Smith and J. J. Smith, “Mode instability in high power fiber amplifiers,” Opt. Express 19(11), 10180–10192 (2011). [CrossRef] [PubMed]

10.

T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H.-J. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, “Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers,” Opt. Express 19(14), 13218–13224 (2011). [CrossRef] [PubMed]

11.

B. Ward, C. Robin, and I. Dajani, “Origin of thermal modal instabilities in large mode area fiber amplifiers,” Opt. Express 20(10), 11407–11422 (2012). [CrossRef] [PubMed]

12.

H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express 20(14), 15710–15722 (2012). [CrossRef] [PubMed]

13.

F. Stutzki, H.-J. Otto, F. Jansen, C. Gaida, C. Jauregui, J. Limpert, and A. Tünnermann, “High-speed modal decomposition of mode instabilities in high-power fiber lasers,” Opt. Lett. 36(23), 4572–4574 (2011). [CrossRef] [PubMed]

14.

C. Jauregui, T. Eidam, J. Limpert, and A. Tünnermann, “The impact of modal interference on the beam quality of high-power fiber amplifiers,” Opt. Express 19(4), 3258–3271 (2011). [CrossRef] [PubMed]

15.

K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett. 37(12), 2382–2384 (2012). [CrossRef] [PubMed]

16.

K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Theoretical analysis of mode instability in high-power fiber amplifiers,” Opt. Express 21(2), 1944–1971 (2013). [CrossRef] [PubMed]

17.

M. M. Johansen, K. R. Hansen, M. Laurila, T. T. Alkeskjold, and J. Lægsgaard, “Estimating modal instability threshold for photonic crystal rod fiber amplifiers,” Opt. Express 21(13), 15409–15417 (2013). [CrossRef] [PubMed]

18.

L. Dong, “Stimulated thermal Rayleigh scattering in optical fibers,” Opt. Express 21(3), 2642–2656 (2013). [CrossRef] [PubMed]

19.

NKT Photonics A/S, “Ytterbium Doped Double Clad Fibers With Large Mode Area,” <http://nktphotonics.com/side5319.html> (2 January 2013). http://nktphotonics.com/side5319.html.

20.

I. Manek-Hönninger, J. Boullet, T. Cardinal, F. Guillen, S. Ermeneux, M. Podgorski, R. Bello Doua, and F. Salin, “Photodarkening and photobleaching of an ytterbium-doped silica double-clad LMA fiber,” Opt. Express 15(4), 1606–1611 (2007). [CrossRef] [PubMed]

21.

M. Leich, U. Röpke, S. Jetschke, S. Unger, V. Reichel, and J. Kirchhof, “Non-isothermal bleaching of photodarkened Yb-doped fibers,” Opt. Express 17(15), 12588–12593 (2009). [CrossRef] [PubMed]

22.

M. Leich, S. Jetschke, S. Unger, and J. Kirchhof, “Temperature influence on the photodarkening kinetics in Yb-doped silica fibers,” J. Opt. Soc. Am. B 28(1), 65–68 (2011). [CrossRef]

OCIS Codes
(060.2280) Fiber optics and optical communications : Fiber design and fabrication
(060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
(140.6810) Lasers and laser optics : Thermal effects
(060.4005) Fiber optics and optical communications : Microstructured fibers

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: June 7, 2013
Revised Manuscript: August 27, 2013
Manuscript Accepted: September 4, 2013
Published: September 10, 2013

Citation
Mette Marie Johansen, Marko Laurila, Martin D. Maack, Danny Noordegraaf, Christian Jakobsen, Thomas Tanggaard Alkeskjold, and Jesper Lægsgaard, "Frequency resolved transverse mode instability in rod fiber amplifiers," Opt. Express 21, 21847-21856 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-19-21847


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B27(11), B63–B92 (2010). [CrossRef]
  2. T. T. Alkeskjold, M. Laurila, L. Scolari, and J. Broeng, “Single-mode ytterbium-doped large-mode-area photonic bandgap rod fiber amplifier,” Opt. Express19(8), 7398–7409 (2011). [CrossRef] [PubMed]
  3. M. Laurila, M. M. Jørgensen, K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Distributed mode filtering rod fiber amplifier delivering 292W with improved mode stability,” Opt. Express20(5), 5742–5753 (2012). [CrossRef] [PubMed]
  4. C.-H. Liu, G. Chang, N. Litchinitser, D. Guertin, N. Jacobsen, K. Tankala, and A. Galvanauskas, “Chirally Coupled Core Fibers at 1550-nm and 1064-nm for Effectively Single-Mode Core Size Scaling,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest Series (CD) (Optical Society of America, 2007), paper CTuBB3.
  5. F. Jansen, F. Stutzki, H.-J. Otto, M. Baumgartl, C. Jauregui, J. Limpert, and A. Tünnermann, “The influence of index-depressions in core-pumped Yb-doped large pitch fibers,” Opt. Express18(26), 26834–26842 (2010). [CrossRef] [PubMed]
  6. D. C. Brown and H. J. Hoffman, “Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers,” IEEE J. Quantum Electron.37(2), 207–217 (2001). [CrossRef]
  7. M.-A. Lapointe, S. Chatigny, M. Piché, M. Cain-Skaff, and J.-N. Maran, “Thermal effects in high power cw fiber lasers,” Proc. SPIE7195, 71951U, 71951U-11 (2009). [CrossRef]
  8. J. Limpert, T. Schreiber, A. Liem, S. Nolte, H. Zellmer, T. Peschel, V. Guyenot, and A. Tünnermann, “Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation,” Opt. Express11(22), 2982–2990 (2003). [CrossRef] [PubMed]
  9. A. V. Smith and J. J. Smith, “Mode instability in high power fiber amplifiers,” Opt. Express19(11), 10180–10192 (2011). [CrossRef] [PubMed]
  10. T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H.-J. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, “Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers,” Opt. Express19(14), 13218–13224 (2011). [CrossRef] [PubMed]
  11. B. Ward, C. Robin, and I. Dajani, “Origin of thermal modal instabilities in large mode area fiber amplifiers,” Opt. Express20(10), 11407–11422 (2012). [CrossRef] [PubMed]
  12. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann, “Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers,” Opt. Express20(14), 15710–15722 (2012). [CrossRef] [PubMed]
  13. F. Stutzki, H.-J. Otto, F. Jansen, C. Gaida, C. Jauregui, J. Limpert, and A. Tünnermann, “High-speed modal decomposition of mode instabilities in high-power fiber lasers,” Opt. Lett.36(23), 4572–4574 (2011). [CrossRef] [PubMed]
  14. C. Jauregui, T. Eidam, J. Limpert, and A. Tünnermann, “The impact of modal interference on the beam quality of high-power fiber amplifiers,” Opt. Express19(4), 3258–3271 (2011). [CrossRef] [PubMed]
  15. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett.37(12), 2382–2384 (2012). [CrossRef] [PubMed]
  16. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Theoretical analysis of mode instability in high-power fiber amplifiers,” Opt. Express21(2), 1944–1971 (2013). [CrossRef] [PubMed]
  17. M. M. Johansen, K. R. Hansen, M. Laurila, T. T. Alkeskjold, and J. Lægsgaard, “Estimating modal instability threshold for photonic crystal rod fiber amplifiers,” Opt. Express21(13), 15409–15417 (2013). [CrossRef] [PubMed]
  18. L. Dong, “Stimulated thermal Rayleigh scattering in optical fibers,” Opt. Express21(3), 2642–2656 (2013). [CrossRef] [PubMed]
  19. NKT Photonics A/S, “Ytterbium Doped Double Clad Fibers With Large Mode Area,” < http://nktphotonics.com/side5319.html > (2 January 2013). http://nktphotonics.com/side5319.html .
  20. I. Manek-Hönninger, J. Boullet, T. Cardinal, F. Guillen, S. Ermeneux, M. Podgorski, R. Bello Doua, and F. Salin, “Photodarkening and photobleaching of an ytterbium-doped silica double-clad LMA fiber,” Opt. Express15(4), 1606–1611 (2007). [CrossRef] [PubMed]
  21. M. Leich, U. Röpke, S. Jetschke, S. Unger, V. Reichel, and J. Kirchhof, “Non-isothermal bleaching of photodarkened Yb-doped fibers,” Opt. Express17(15), 12588–12593 (2009). [CrossRef] [PubMed]
  22. M. Leich, S. Jetschke, S. Unger, and J. Kirchhof, “Temperature influence on the photodarkening kinetics in Yb-doped silica fibers,” J. Opt. Soc. Am. B28(1), 65–68 (2011). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited