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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editor: Gregory W. Faris
  • Vol. 4, Iss. 11 — Oct. 21, 2009
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Highly stable and efficient erbium-doped 2.8 μm all fiber laser

Martin Bernier, Dominic Faucher, Nicolas Caron, and Réal Vallée  »View Author Affiliations


Optics Express, Vol. 17, Issue 19, pp. 16941-16946 (2009)
http://dx.doi.org/10.1364/OE.17.016941


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Abstract

We demonstrate the efficient and stable CW laser operation at 2.824 μm of a diode-pumped erbium-doped fluoride fiber laser employing an intracore fiber Bragg grating high reflector. An output power of 5 W and an optical-to-optical conversion efficiency of 32% are reported. The temporal and spectral stability of the laser represent a significant improvement over previous work. This report paves the way to the commercialization of compact and stable fiber lasers for spectroscopic and medical applications.

© 2009 OSA

1. Introduction

In this paper, we report the operation of an all-fiber, highly stable, efficient erbium-doped fluoride fiber laser. The maximum output power of 5W at a stable wavelength of 2824nm was enabled by the use of a high reflector (HR), which is a FBG written directly in the highly-doped fluoride fiber core. The optical-to-optical conversion efficiency of 32% is significantly higher than previously reported. The peak-to-peak power fluctuations were observed to be less than ± 0.3%.

2. Experiment

The fiber used in the experiment is a 6.42m, 7 mol% singly Er3+-doped fluoride fiber provided by Le Verre Fluoré. The standard ZBLAN composition was modified to permit this level of doping. The pump core of the double-clad fiber had a 160x135 μm D-shaped geometry and a numerical aperture (NA) >0.46. The 8 μm diameter, 0.24 NA fiber core ensured single-mode operation of the fiber laser. The pump absorption at 976 nm was measured at 1.65dB/m through a cutback experiment, while the background losses for the laser signal at 2.8μm were measured to be 0.18 dB/m. The fiber laser cavity configuration used to test the laser operation is presented in Fig. 1
Fig. 1 Erbium-doped all fiber laser configuration with a FBG acting as the high reflector.
.

As shown in Fig. 1, the doped fiber was pumped through the HR using the combined output of 6 pump diodes (Alfalight AM6-976B-10-604) coupled through a 7x1 multimode pump combiner (ITF Labs MMC07011011). This setup provided up to 36W of available pump power at the output of the 125 μm diameter, 0.46 NA fiber of the pump combiner. The pump power was launched into the doped fiber by butt-coupling. A launch efficiency of 84% was inferred from the results of the cutback experiment. To minimize thermal effects at the launch end, a water-cooled fiber mount was used to hold both the launch fiber end and the HR, although active air cooling would have likely been sufficient given the high launch efficiency. The length of the segment between the pump fiber end and the FBG was roughly 7 cm. Both fiber ends were carefully polished to a perpendicular, smooth finish. The ~4% Fresnel reflection provided the low reflectivity output reflector of the fiber laser cavity. During our early experiments, we systematically observed catastrophic optical damage (COD) of the output fiber end-face for output powers of about 2 W. The cause of this COD was attributed to the presence of moisture at the ZBLAN-air interface. To prevent this, we found it necessary to purge the output fiber end-face from moisture, which was accomplished by blowing pressurized nitrogen on the fiber tip. A dichroic mirror (≥95% reflectivity at 976nm) was used to remove the ~8% residual pump power from the collimated output beam. The output spectrum of the fiber laser was measured with a Digikrom DK480 monochromator and a PbSe detector, with a spectral resolution of about 0.1nm, while the laser output power was monitored using a thermopile power meter (Gentec UP19K-15S-H5).

The HR was written using the method described in [16

16. M. Bernier, D. Faucher, R. Vallée, A. Saliminia, G. Androz, Y. Sheng, and S. L. Chin, “Bragg gratings photoinduced in ZBLAN fibers by femtosecond pulses at 800 nm,” Opt. Lett. 32(5), 454–456 (2007). [CrossRef] [PubMed]

] based on the interaction of femtosecond laser pulses at a central wavelength of 806 nm. The polymer coating of the fiber was removed prior to writing the FBG and a low index polyacrylate was subsequently applied to ensure low pump guiding losses and to protect the fiber. The phase mask used in the experiment had a uniform pitch of 1903.5 nm, giving a first-order Bragg reflection in the Er-doped fluoride fiber at 2822.5nm. The transmission spectrum of the FBG was monitored using a ZBLAN-based super-continuum light source developed in-house which covered a bandwidth extending from 1000nm to 3750nm. After the inscription process, the FBG was thermally annealed so as to stabilize the FBG’s reflectivity. The DK480 monochromator was used to measure the transmission spectrum of the grating with a spectral resolution of 0.4nm. Figure 2
Fig. 2 Measured transmission spectrum of the FBG written in the Er3+-doped fluoride fiber (exposure time: 15s, grating length: 8mm).
shows the transmission spectrum of the annealed FBG, which was written in the highly-doped fluoride fiber.

The maximum reflectivity of the grating occurs at 2822.5 nm with a full width at half maximum (FWHM) of 2.4 nm. The throughput losses of less than 5% were evaluated separately through a cut-back measurement outside of the FBG’s bandwidth at 2830 nm, so as not to interfere with the FBG transmission dip. These measurements imply a peak reflectivity of at least 95% at 2822.5 nm. The pump transmission through the highly reflective FBG was measured to be 97%.

3. Results and discussion

Figure 3
Fig. 3 Laser output power vs launched pump power.
shows the output power of the laser with respect to the launched pump power.

A maximum of 5W of output power was measured for a launched pump power of 20.5W, indicating an overall laser efficiency of 24%. For higher pump powers, the pump fiber end was subject to thermally-induced damage. The laser threshold could not be measured directly due to the unstable operation of the pump source near threshold, but a value of about 60 mW was inferred from a linear extrapolation of the results at low pump powers. For output powers <2.5W, the laser slope efficiency reached 29% with respect to the launched pump power. By accounting for the residual pump power of ~8% of the launched pump power, the optical-to-optical conversion efficiency was 32%. This is close to the Stokes efficiency of 34% but far from the theoretical efficiency of >50% inherent to the pump energy recycling scheme in such a highly doped (7 mol.%) fiber [15

15. M. Pollnau and S. D. Jackson, “Energy recycling versus lifetime quenching in erbium-doped 3-μm fiber lasers,” IEEE J. Quantum Electron. 38(2), 162–169 (2002). [CrossRef]

]. Our calculations, based on a model similar to Pollnau’s, suggest that this discrepancy could be due to lower energy transfer parameters in our fiber, which would arise from a reduced amount of clusters. Also, there is a noticeable decrease of the slope efficiency at output powers >2.5W. The origin of this is unclear but it might be due to thermal effects, pump ESA from the upper laser level or to a variation of the overall gain with increasing pump power, which has been reported before [12

12. X. Zhu and R. Jain, “Compact 2 W wavelength-tunable Er:ZBLAN mid-infrared fiber laser,” Opt. Lett. 32(16), 2381–2383 (2007). [CrossRef] [PubMed]

]. We should note that a similar saturation behavior has been reported in the past [19

19. S. Bedo, M. Pollnau, W. Luthy, and H. P. Weber, “Saturation of the 2.71μm laser output in erbium-doped ZBLAN fibers,” Opt. Commun. 116(1-3), 81–86 (1995). [CrossRef]

] and was attributed to simultaneous lasing at 850nm from the 4S3/24I13/2 transition. However, pumping in the 980 nm has been reported to prevent this from occurring.

The emission spectrum of the laser shown in Fig. 4
Fig. 4 Laser output spectrum for an output power of 3.24W. The inset shows the corresponding narrowband laser emission spectrum measured with a resolution of 0.1nm.
was measured for an output power of 3.24W and the inset shows a blow-up measured with a 0.1nm resolution.

The FWHM and the central wavelength were 0.22nm and 2823.9nm, respectively. We attribute the 1.4nm offset between the peak emission wavelength and the Bragg wavelength of 2822.5nm to the thermal expansion of the fiber leading to an increase of the Bragg wavelength. In fact, measurements of the output spectrum as a function of the output power indicated a spectral drift of the Bragg wavelength of about 0.4nm per watt of laser emission.

The temporal stability of the fiber laser output was monitored using a thermopile detector (Spectra Physics, 407A) with a 0.5s response time. Figure 5
Fig. 5 Output power stability for different output powers ranging from 0.85W up to 5W
shows the output power stability of the laser over an observation of 100s at different output powers ranging from 0.85W up to 5W.

Peak-to-peak fluctuations of less than ± 0.3% are measured at 5W of output power. The largest peak-to-peak fluctuations ( ± 0.8%) were observed at output power of 0.85W. A liquid-nitrogen-cooled InSb photodetector (Judson J10D) was also used to confirm the laser stability on a time-scale of 0.25s (acquisition rate of 125 kHz) in a similar laser cavity and no rapid fluctuations larger than those observed in Fig. 5 has been noted.

4. Conclusion

Acknowledgment

This research was supported by the Canadian Institute for Photonic Innovations (CIPI), the Ministère du Developpement Economique, de l’Innovation et de l’Exportation (MDEIE), the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT), the Natural Sciences and Engineering Research Council of Canada (NSERC), Le Verre Fluoré and the Canadian Foundation for Innovation (CFI). The authors thank Gwenaël Mazé of Le Verre Fluoré for helpful discussions.

References and links

1.

S. D. Jackson and A. Lauto, “Diode-pumped fiber lasers: a new clinical tool?” Lasers Surg. Med. 30(3), 184–190 (2002). [CrossRef] [PubMed]

2.

V. Raghunathan, D. Borlaug, R. R. Rice, and B. Jalali, “Demonstration of a Mid-infrared silicon Raman amplifier,” Opt. Express 15(22), 14355–14362 (2007). [CrossRef] [PubMed]

3.

F. Tittle, D. Richter, and A. Fried, “Mid-Infrared laser applications in spectroscopy,” Top. Appl. Phys. 89, 445 (2003).

4.

J. Tafoya, J. Pierce, R. K. Jain, and B. Wong, “Efficient and compact high-power mid-IR (3μm) lasers for surgical applications” in Lasers in Surgery, Advanced Characterization, Therapeutics and Systems XIV, K. E. Bartels, L. S. Bass, eds., Proc. SPIE 5312, 218–222 (2004).

5.

S. D. Jackson, T. A. King, and M. Pollnau, “Diode-pumped 1.7-W erbium 3-mum fiber laser,” Opt. Lett. 24(16), 1133–1135 (1999). [CrossRef]

6.

B. Srinivasan, J. Tafoya, and R. K. Jain, “High-power “Watt-level” CW operation of diode-pumped 2.7 aem fiber lasers using efficient cross-relaxation and energy transfer mechanisms,” Opt. Express 4(12), 490–495 (1999). [CrossRef] [PubMed]

7.

S. D. Jackson, “Single-transverse-mode 2.5-W holmium-doped fluoride fiber laser operating at 2.86 microm,” Opt. Lett. 29(4), 334–336 (2004). [CrossRef] [PubMed]

8.

Y. H. Tsang, A. E. El-Taher, T. A. King, and S. D. Jackson, “Efficient 2.96μm dysprosium-doped fluoride fiber laser pumped with a ND:YAG laser operating at 1.3μm,” Opt. Lett. 29, 334–336 (2004).

9.

T. Sandrock, D. Fischer, P. Glas, M. Leitner, M. Wrage, and A. Diening, “Diode-pumped 1-W Er-doped fluoride glass M-profile fiber laser emitting at 2.8 mum,” Opt. Lett. 24(18), 1284–1286 (1999). [CrossRef]

10.

S. D. Jackson, T. A. King, and M. Pollnau, “Efficient high-power operation of erbium 3μm fiber laser diode pumped at 975nm,” Electron. Lett. 36(3), 223–224 (2000). [CrossRef]

11.

X. Zhu and R. Jain, “Numerical analysis and experimental results of high-power Er/Pr:ZBLAN 2.7 microm fiber lasers with different pumping designs,” Appl. Opt. 45(27), 7118–7125 (2006). [CrossRef] [PubMed]

12.

X. Zhu and R. Jain, “Compact 2 W wavelength-tunable Er:ZBLAN mid-infrared fiber laser,” Opt. Lett. 32(16), 2381–2383 (2007). [CrossRef] [PubMed]

13.

D. J. Coleman, T. A. King, D.-K. Ko, and J. Lee, “Q-switch operation of a 2.7μm cladding-pumped Er3+/Pr3+ codoped ZBLAN fiber laser,” Opt. Commun. 236(4-6), 379–385 (2004). [CrossRef]

14.

X. Zhu and R. Jain, “10-W-level diode-pumped compact 2.78 microm ZBLAN fiber laser,” Opt. Lett. 32(1), 26–28 (2007). [CrossRef]

15.

M. Pollnau and S. D. Jackson, “Energy recycling versus lifetime quenching in erbium-doped 3-μm fiber lasers,” IEEE J. Quantum Electron. 38(2), 162–169 (2002). [CrossRef]

16.

M. Bernier, D. Faucher, R. Vallée, A. Saliminia, G. Androz, Y. Sheng, and S. L. Chin, “Bragg gratings photoinduced in ZBLAN fibers by femtosecond pulses at 800 nm,” Opt. Lett. 32(5), 454–456 (2007). [CrossRef] [PubMed]

17.

G. Androz, D. Faucher, M. Bernier, and R. Vallée, “Monolithic fluoride-fiber laser at 1480 nm using fiber Bragg gratings,” Opt. Lett. 32(10), 1302–1304 (2007). [CrossRef] [PubMed]

18.

G. Androz, M. Bernier, D. Faucher, and R. Vallée, “2.3 W single transverse mode thulium-doped ZBLAN fiber laser at 1480 nm,” Opt. Express 16(20), 16019–16031 (2008). [CrossRef] [PubMed]

19.

S. Bedo, M. Pollnau, W. Luthy, and H. P. Weber, “Saturation of the 2.71μm laser output in erbium-doped ZBLAN fibers,” Opt. Commun. 116(1-3), 81–86 (1995). [CrossRef]

OCIS Codes
(140.3500) Lasers and laser optics : Lasers, erbium
(140.3510) Lasers and laser optics : Lasers, fiber
(230.1480) Optical devices : Bragg reflectors

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 23, 2009
Revised Manuscript: August 26, 2009
Manuscript Accepted: August 27, 2009
Published: September 8, 2009

Virtual Issues
Vol. 4, Iss. 11 Virtual Journal for Biomedical Optics

Citation
Martin Bernier, Dominic Faucher, Nicolas Caron, and Réal Vallée, "Highly stable and efficient erbium-doped 2.8 μm all fiber laser," Opt. Express 17, 16941-16946 (2009)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-17-19-16941


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References

  1. S. D. Jackson and A. Lauto, “Diode-pumped fiber lasers: a new clinical tool?” Lasers Surg. Med. 30(3), 184–190 (2002). [CrossRef] [PubMed]
  2. V. Raghunathan, D. Borlaug, R. R. Rice, and B. Jalali, “Demonstration of a Mid-infrared silicon Raman amplifier,” Opt. Express 15(22), 14355–14362 (2007). [CrossRef] [PubMed]
  3. F. Tittle, D. Richter, and A. Fried, “Mid-Infrared laser applications in spectroscopy,” Top. Appl. Phys. 89, 445 (2003).
  4. J. Tafoya, J. Pierce, R. K. Jain, and B. Wong, “Efficient and compact high-power mid-IR (3μm) lasers for surgical applications,” Proc. SPIE 5312, 218–222 (2004).
  5. S. D. Jackson, T. A. King, and M. Pollnau, “Diode-pumped 1.7-W erbium 3-mum fiber laser,” Opt. Lett. 24(16), 1133–1135 (1999). [CrossRef]
  6. B. Srinivasan, J. Tafoya, and R. K. Jain, “High-power “Watt-level” CW operation of diode-pumped 2.7 aem fiber lasers using efficient cross-relaxation and energy transfer mechanisms,” Opt. Express 4(12), 490–495 (1999). [CrossRef] [PubMed]
  7. S. D. Jackson, “Single-transverse-mode 2.5-W holmium-doped fluoride fiber laser operating at 2.86 microm,” Opt. Lett. 29(4), 334–336 (2004). [CrossRef] [PubMed]
  8. Y. H. Tsang, A. E. El-Taher, T. A. King, and S. D. Jackson, “Efficient 2.96μm dysprosium-doped fluoride fiber laser pumped with a ND:YAG laser operating at 1.3μm,” Opt. Lett. 29, 334–336 (2004).
  9. T. Sandrock, D. Fischer, P. Glas, M. Leitner, M. Wrage, and A. Diening, “Diode-pumped 1-W Er-doped fluoride glass M-profile fiber laser emitting at 2.8 mum,” Opt. Lett. 24(18), 1284–1286 (1999). [CrossRef]
  10. S. D. Jackson, T. A. King, and M. Pollnau, “Efficient high-power operation of erbium 3μm fiber laser diode pumped at 975nm,” Electron. Lett. 36(3), 223–224 (2000). [CrossRef]
  11. X. Zhu and R. Jain, “Numerical analysis and experimental results of high-power Er/Pr:ZBLAN 2.7 microm fiber lasers with different pumping designs,” Appl. Opt. 45(27), 7118–7125 (2006). [CrossRef] [PubMed]
  12. X. Zhu and R. Jain, “Compact 2 W wavelength-tunable Er:ZBLAN mid-infrared fiber laser,” Opt. Lett. 32(16), 2381–2383 (2007). [CrossRef] [PubMed]
  13. D. J. Coleman, T. A. King, D.-K. Ko, and J. Lee, “Q-switch operation of a 2.7μm cladding-pumped Er3+/Pr3+ codoped ZBLAN fiber laser,” Opt. Commun. 236(4-6), 379–385 (2004). [CrossRef]
  14. X. Zhu and R. Jain, “10-W-level diode-pumped compact 2.78 microm ZBLAN fiber laser,” Opt. Lett. 32(1), 26–28 (2007). [CrossRef]
  15. M. Pollnau and S. D. Jackson, “Energy recycling versus lifetime quenching in erbium-doped 3-μm fiber lasers,” IEEE J. Quantum Electron. 38(2), 162–169 (2002). [CrossRef]
  16. M. Bernier, D. Faucher, R. Vallée, A. Saliminia, G. Androz, Y. Sheng, and S. L. Chin, “Bragg gratings photoinduced in ZBLAN fibers by femtosecond pulses at 800 nm,” Opt. Lett. 32(5), 454–456 (2007). [CrossRef] [PubMed]
  17. G. Androz, D. Faucher, M. Bernier, and R. Vallée, “Monolithic fluoride-fiber laser at 1480 nm using fiber Bragg gratings,” Opt. Lett. 32(10), 1302–1304 (2007). [CrossRef] [PubMed]
  18. G. Androz, M. Bernier, D. Faucher, and R. Vallée, “2.3 W single transverse mode thulium-doped ZBLAN fiber laser at 1480 nm,” Opt. Express 16(20), 16019–16031 (2008). [CrossRef] [PubMed]
  19. S. Bedo, M. Pollnau, W. Luthy, and H. P. Weber, “Saturation of the 2.71μm laser output in erbium-doped ZBLAN fibers,” Opt. Commun. 116(1-3), 81–86 (1995). [CrossRef]

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