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1.7-W femtosecond fiber-based source at 3.6 µm
Conference Paper · October 2016
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Frontiers in Optics/Laser Science 2016 © OSA 2016
1.7-W femtosecond fiber-based source at 3.6 µm
Simon Duval,1,* Jean-Christophe Gauthier,1 Louis-Rafaël Robichaud,1 Pascal Paradis,1 Michel Olivier,1,2
Vincent Fortin,1 Martin Bernier,1 Michel Piché,1 and Réal Vallée1
1
Centre d’optique, photonique et laser (COPL), Université Laval, Québec G1V0A6, Canada
2
Département de physique, Cégep Garneau, Québec G1S4S3, Canada
*Corresponding author: simon.duval.2@ulaval.ca
Abstract: We demonstrate a watt-level femtosecond fiber source that produces stable sub-250-fs
solitons tunable from 2.8 to 3.6 µm with peak powers up to 200 kW. Perspectives for scaling up
the performance of this system are also discussed.
OCIS codes: (140.3070) Infrared and far-infrared lasers; (140.3600) Lasers, tunable; (060.5530) Pulse propagation and
temporal solitons.
1. Introduction
Promising applications including spectroscopy, remote sensing, laser surgery and material processing are driven by
the development of ultrafast laser technologies in the mid-infrared (mid-IR) spectral range (2 to 20 µm) [1]. Fluoride
fiber lasers are certainly among the best candidates for such applications as they can offer the inherent advantages of
fiber lasers while benefiting from several mid-IR laser transitions through the incorporation of various rare-earth
dopants such as Er3+, Ho3+ or Dy3+ [2].
Moreover, the recent demonstration of soliton fiber lasers operating at 2.8 µm that produce pulses as short as 200 fs
with peak powers up to 23 kW [3-5] brings forward the power scaling potential of such ultrafast fiber lasers in the
mid-IR. The reduced effective nonlinearities and the high anomalous dispersion also make fluoride fibers attractive
hosts for the generation of high-energy solitons that can be tuned further into the mid-infrared through soliton selffrequency shift (SSFS). Tang et al. recently reported an impressive fiber source tunable from 2 to 4.3 µm based on
such process in fluoride glass fibers, but the use of a pump fiber laser in the near-IR limited their average output
power to a few milliwatts [6].
Here, we use a mid-IR femtosecond fiber oscillator combined with a simple amplifying architecture consisting of a
monolithic segment of Er-doped fluoride fiber to efficiently generate clean and spectrally isolated solitons that are
tunable from 2.8 to 3.6 µm. Spectral tunability is achieved by simply adjusting the pump power in the amplifier.
This system allows the generation of sub-250-fs soliton pulses with peak powers up to 200 kW, corresponding to
average powers above 1 W over the whole 3 to 3.6 µm spectral region.
2. Experimental setup
The fiber laser system is presented in Fig. 1. The mode-locked fiber oscillator (similar to the one presented in [5])
generates stable 440-fs, 5-nJ soliton pulses at a repetition rate of 57.9 MHz. Both the oscillator and the amplifier use
a double-clad 7 % mol. Er-doped zirconium-fluoride fiber provided by Le Verre Fluoré (core Ø = 15 µm, NA =
0.12). The fiber amplifier is pumped via a multimode laser diode providing up to 50 W at 980 nm.
Figure 1 Schematic of the fiber laser system. L1: Collimation lens for the pump beam; DM: Dichroic mirror (HR at 980 nm and HT at 2.8 µm);
L2 = Aspheric ZnSe lens (f = 12.5 mm); CMS: Cladding mode stripper.
FF2B.5.pdf
Frontiers in Optics/Laser Science 2016 © OSA 2016
In order to efficiently amplify the main soliton pulse and maximize its shift towards longer wavelengths, we stripped
the pump beam at 1.25 m from the input with a cladding mode stripper. The first segment thus acts as the amplifier
while the second unpumped segment (L ̴ 21 m) shifts the amplified soliton at longer wavelengths.
The output spectra measured with a monochromator along with a nitrogen-cooled InSb detector are presented in Fig.
2 for different pump powers. These spectra were corrected to compensate for the spectral response of the
measurement system and were normalized to the corresponding output average power of the signal. As the pump
power is increased, the main soliton is amplified and gradually shifts toward longer wavelengths until a second
soliton is formed from the residual amplified background. The durations and the energies of the main shifted
solitons were estimated from each spectrum and validated with the values obtained with a mid-IR intensity
autocorrelator and with a power meter after filtering the signal to isolate the main soliton. At 50 W of pump power,
30-nJ, 240-fs pulses with an estimated peak power of 109 kW and a corresponding average power of 1.7 W are
generated at 3.6 µm. When reducing the unpumped segment to ̴ 7m, the fiber system generates stable 160-fs soliton
pulses at 3.4 µm with an energy of 37 nJ and a peak power of more than 200 kW. With a corresponding average
power of 2 W at 3.4 µm, such fiber laser system actually surpasses the best performances reported so far from a CW
fluoride fiber laser around 3.4 µm [7].
Figure 2 Normalized output spectra for different input pump powers. The filled part of each curve
represents the spectrum of the main shifted soliton.
3. Conclusion
We demonstrated a simple and efficient fiber-based system for the generation of high-peak-power femtosecond
soliton pulses tunable from 2.8 to 3.6 µm. With watt-level average powers, this source could be used for polymer
processing at 3.4 µm or ablation of biological tissues at 2.94 µm. Further optimization of this system by changing
the fiber’s dispersive and nonlinear properties or by using indium-fluoride glass fiber could extend further the tuning
range up to 6 µm, enabling promising applications in spectroscopy, remote sensing as well as in infrared
countermeasures.
4. References
[1] I. T. Sorokina and K. L. Vodopyanov, Solid-State Mid-Infrared Laser Sources, eds., Vol. 89 of Top. Appl. Phys. (Springer, 2003).
[2] S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser”, Nat. Photon. 6, 423-431 (2012).
[3] S. Duval, M. Bernier, V. Fortin, G. Genest, M. Piché, and R. Vallée, “Femtosecond fiber lasers reach the mid-infrared”, Optica 2, 623-626
(2015).
[4] T. Hu, S. D. Jackson, and D. D. Hudson, “Ultrafast pulses from a mid-infrared fiber laser”, Opt. Lett. 18, 4226-4228 (2015).
[5] S. Duval, M. Olivier, V. Fortin, M. Bernier, M. Piché, and R. Vallée, “23-kW peak power femtosecond pulses from a mode-locked fiber ring
laser at 2.8 µm”, Proc. SPIE 9728, 972802 (2016).
[6] Y. Tang, L. G. Wright, K. Charan, T. Wang, C. Xu, and F. W. Wise, “Generation of intense 100-fs solitons tunable from 2 to 4.3 µm in
fluoride fiber”, Optica 3, 948-951 (2016).
[7] V. Fortin, F. Maes, M. Bernier, S.T. Bah, M. D’Auteuil, and R. Vallée, “Watt-level erbium-doped all-fiber laser at 3.44 µm”, Opt. Lett. 41,
559-562 (2016).