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  • Editor: Alan E. Willner
  • Vol. 38, Iss. 2 — Jan. 15, 2013
  • pp: 127–129
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Mid-infrared chalcogenide glass Raman fiber laser

M. Bernier, V. Fortin, N. Caron, M. El-Amraoui, Y. Messaddeq, and R. Vallée  »View Author Affiliations


Optics Letters, Vol. 38, Issue 2, pp. 127-129 (2013)
http://dx.doi.org/10.1364/OL.38.000127


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Abstract

We report the first demonstration of a Raman fiber laser (RFL) emitting in the mid-infrared, above 3 μm. The operation of a single-mode As2S3 chalcogenide glass based RFL at 3.34 μm is demonstrated by using a low-loss Fabry–Pérot cavity formed by a pair of fiber Bragg gratings. A specially designed quasi-cw erbium-doped fluoride fiber laser emitting at 3.005 μm is used to pump the RFL. A laser output peak power of 0.6 W is obtained with a lasing efficiency of 39% with respect to the launched pump power.

© 2013 Optical Society of America

Stimulated Raman scattering is an enabling process allowing for efficient laser operation at almost any desired wavelength, i.e., bridging the gap between rare-earth emission bands. The first generation of cw visible Raman fiber laser (RFL) demonstrated in the 1970s involved bulk components [1

1. R. H. Stolen, A. R. Tynes, and E. P. Ippen, Appl. Phys. Lett. 20, 62 (1972). [CrossRef]

]. Later in the late 1990s, monolithic near-IR RFLs were developed with the availability of low-loss silica-based fibers, bright laser diodes and fiber Bragg gratings (FBGs). A broad wavelength coverage from 1.1 to 1.5 μm was, for instance, reported using a cascade Stokes shifts scheme in a phosphosilicate fiber [2

2. V. I. Karpov, E. M. Dianov, V. M. Paramonov, O. I. Medvedkov, M. M. Bubnov, S. L. Semyonov, S. A. Vasiliev, V. N. Protopopov, O. N. Egorova, V. F. Hopin, A. N. Guryanov, M. P. Bachynski, and W. R. L. Clements, Opt. Lett. 24, 887 (1999). [CrossRef]

]. The power scaling of such an RFL was further demonstrated up to hundreds of watts in cw operation [3

3. Y. Feng, L. R. Taylor, and D. B. Calia, Opt. Express 17, 23678 (2009). [CrossRef]

]. Using GeO2 fibers, this cascade approach was used to extend the wavelength coverage of RFLs slightly beyond 2 μm [4

4. E. M. Dianov, I. A. Bufetov, V. M. Mashinsky, V. B. Neustruev, O. I. Medvedkov, A. V. Shubin, M. A. Melkumov, A. N. Gur’yanov, V. F. Khopin, and M. V. Yashkov, Quantum Electron. 34, 695 (2004). [CrossRef]

]. Recently, RFL emission was reported for the first time in a fluoride glass fiber, [5

5. V. Fortin, M. Bernier, J. Carrier, and R. Vallée, Opt. Lett. 36, 4152 (2011). [CrossRef]

] which offers, in principle, a new alternative for extended spectral coverage in the mid-IR. In fact, the operation wavelength of such a laser was further increased up to 2.23 μm with 3.7 W of output power in cw operation [6

6. V. Fortin, M. Bernier, D. Faucher, J. Carrier, and R. Vallée, Opt. Express 20, 19412 (2012). [CrossRef]

], which represents, to date, the longest emission wavelength reported for an RFL. Unfortunately, fluoride glass fibers exhibit a relatively low Raman gain coefficient [5

5. V. Fortin, M. Bernier, J. Carrier, and R. Vallée, Opt. Lett. 36, 4152 (2011). [CrossRef]

], which somehow hinders their use at longer wavelengths in the cw regime, particularly since the Raman gain coefficient scales inversely with the pump wavelength [7

7. G. P. Agrawal, Nonlinear Fiber Optics (Academic, 2001).

].

A growing number of applications in the fields of biomedicine, manufacturing, spectroscopy, and defense and security are calling for the development of compact and reliable mid-IR coherent radiation sources, especially fiber lasers [8

8. S. D. Jackson, Nat. Photonics 6, 423 (2012). [CrossRef]

,9

9. P. Zhou, X. Wang, Y. Ma, H. Lü, and Z. Liu, Laser Phys. 22, 1744 (2012). [CrossRef]

]. Chalcogenide glass (ChG) fibers are promising in that respect because of their extended transparency in the mid- to far-IR and also because of their very high nonlinearity. For example, the Raman gain coefficient of As2S3 and As2Se3 glasses is typically 50 and 350 times larger, respectively, than that of a fluoride glass [5

5. V. Fortin, M. Bernier, J. Carrier, and R. Vallée, Opt. Lett. 36, 4152 (2011). [CrossRef]

,10

10. R. T. White and T. M. Monro, Opt. Lett. 36, 2351 (2011). [CrossRef]

]. Now, although theoretical studies have been carried out predicting the operation of a ChG-based RFL [11

11. P. Thielen, L. Shaw, J. Sanghera, and I. Aggarwal, Opt. Express 11, 3248 (2003). [CrossRef]

,12

12. J. S. Sanghera, L. B. Shaw, and I. D. Aggarwal, IEEE J. Sel. Top. Quantum Electron. 15, 114 (2009). [CrossRef]

], there has been, to date, only one experimental report of such RFL based on an As2Se3 fiber operating at a wavelength near 2.1 μm [13

13. S. D. Jackson and G. Anzueto-Sánchez, Appl. Phys. Lett. 88, 221106 (2006). [CrossRef]

]. The recent development of high power, single-mode fiber lasers emitting at 3 μm based on erbium-doped fluoride glass (Er-FG) fibers [14

14. D. Faucher, M. Bernier, G. Androz, N. Caron, and R. Vallée, Opt. Lett. 36, 1104 (2011). [CrossRef]

] combined with the demonstration of the writing of high reflectivity, low loss and robust FBGs in single-mode As2S3 fibers [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

] made the wavelength extension of RFLs to the mid-IR technically achievable.

In this Letter, we report on the first demonstration of an RFL emitting in the mid-IR, above 3 μm. The operation of a single-mode As2S3 ChG-based RFL emitting at 3.34 μm is reported based on a Fabry–Pérot cavity formed by a pair of FBGs written in a 3 m long segment of a low-loss single-mode As2S3 fiber. An output peak power of 0.6 W is demonstrated at 3.34 μm with a lasing efficiency of 39% with respect to the launched pump power. An Er-FG fiber laser emitting at 3.005 μm in the quasi-cw (QCW) regime is used to pump the RFL.

The experimental setup is shown in Fig. 1. The pump fiber laser operating at 3.005 μm was specially designed for this project, based on the same basic architecture as described in [14

14. D. Faucher, M. Bernier, G. Androz, N. Caron, and R. Vallée, Opt. Lett. 36, 1104 (2011). [CrossRef]

]. Accordingly, a high finesse Fabry–Pérot cavity was used to force laser operation of the Er-FG fiber laser to the extreme value of 3.005 μm, which is very far from the erbium ions emission peak occurring near 2.8 μm. This pump laser was operated in the QCW regime [16

16. D. Faucher, N. Caron, M. Bernier, and R. Vallée, in Lasers, Sources, and Related Photonic Devices, OSA Technical Digest (OSA, 2012), paper FTh4A.6.

] by modulating the 980 nm pump diodes at a frequency of 20 Hz and a duty-cycle of 10%. In such QCW operation, the pulse train consists of 4–5 ms pulses having a peak power of about 10 W. These operating conditions were set to obtain the relatively high output peak power required for the onset of the stimulated Raman process while maintaining a ten-fold smaller average power to prevent thermo-mechanical instabilities of the free-space coupling of the pump beam into the single-mode ChG fiber.

Fig. 1. Experimental setup of the As2S3-based 3.34 μm RFL. LPF, long-pass filter; FBG1, Stokes cavity high reflector (HR); FBG2, Stokes cavity low reflector (LR); FBG3, residual pump high reflector (HR).

The single-mode output of the 3 μm pump fiber laser (MFD=20μm at λ=3.005μm, NA=0.12) was collimated using an f=12.7mm ZnSe aspheric lens (L1 in Fig. 1) (Thorlabs No. AL72512-E). A long-pass filter (LPF in Fig. 1) having a cutoff wavelength of 2.85 μm, fabricated in-house on a sapphire substrate, was placed in the collimated beam to eliminate the undesired spectral components of the 2.7–2.8 μm band emitted at the beginning of the QCW pulse [16

16. D. Faucher, N. Caron, M. Bernier, and R. Vallée, in Lasers, Sources, and Related Photonic Devices, OSA Technical Digest (OSA, 2012), paper FTh4A.6.

]. A second aspheric lens having a 4 mm focal length (L2 in Fig. 1) (Thorlabs No. C036TME-D) was used to couple the 3 μm collimated pump laser through the single-mode As2S3 fiber core. The pump to laser launching efficiency was measured by cutback to be 26% resulting in a maximum injected pump peak power of 2.6 W in the Raman cavity for 10 W of available peak power at the output of the 3 μm pump laser. The corresponding 74% losses include the transmission losses of both the lenses and the LPF (26%), the mode mismatch between the incident beam and the As2S3 fiber mode (53%), the 17% Fresnel losses at the input fiber face of the As2S3 fiber (n2.4) as well as the losses of a 0.3 m segment of As2S3 fiber before the laser cavity (9%).

The glass synthesis and purification processes were performed at COPL Laboratories while the fiber drawing was carried out at CorActive High-Tech Inc. Details on the fiber fabrication and characterization are available in [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

]. The single-mode As2S3 fiber has a core/cladding diameter of 4.0/145μm, respectively, recoated with a 310 μm diameter standard acrylate jacket. The numerical aperture of the fiber is 0.36, which provides single-mode operation at a wavelength above 1.9μm and good core confinement up to a wavelength of 4.0μm. The 3 μm pump wavelength was set in order to push the first Stokes shift away from the OH and SH residual absorption bands to reach the low loss spectral window of the fiber, which begins at a wavelength of about 3.25 μm [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

]. In a 3.005 μm pumping condition, the peak Raman gain wavelength is at 3.345 μm considering a peak Stokes shift in As2S3 of 10.2 THz [10

10. R. T. White and T. M. Monro, Opt. Lett. 36, 2351 (2011). [CrossRef]

]. The corresponding pump (3.005 μm) and signal (3.345 μm) loss coefficients of the single-mode As2S3 fiber are 1.4dB/m and 0.1dB/m, respectively [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

].

Three FBGs were written through the polymer coating of a 3 m long segment of As2S3 fiber using 800 nm femtosecond pulses and a phase-mask as described in [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

]. Close to the input fiber end, a high reflectivity FBG (FBG1 in Fig. 1) was written at 3.340 μm with a maximum reflectivity of >99% and a FWHM bandwidth of 2.2 nm to act as the input Stokes cavity coupler. Close to the output fiber end, a second FBG (FBG2 on Fig. 1) was written at 3.340 μm with a maximum reflectivity of 63% and a FWHM bandwidth of 0.6 nm to act as the output Stokes cavity coupler. This output coupler was mounted in a mechanical strain apparatus to manually optimize its spectral overlap with the input coupler (FBG1), which was found to be critical considering the narrow spectral width of both the input and output couplers. Finally, a third FBG was written close to the output fiber end (FBG3 on Fig. 1) to reflect the residual 3 μm pump laser so as to enhance the pump intensity in the Raman cavity by recycling the residual pump power, thereby reducing the laser threshold by 25%. This pump reflector was written with a maximum reflectivity greater than 95% at a central wavelength of 3.005 μm with a FWHM bandwidth of 4 nm to spectrally overlap the pump source. The three FBGs were thermally annealed at 100°C during 30 min to stabilize their spectral responses [15

15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

]. The transmission spectra of these FBGs were characterized at a spectral resolution of 0.4 nm using a fluoride fiber-based supercontinuum source (built in-house) together with a grating-based scanning spectrometer (Digikrom DK480) coupled to a nitrogen-cooled InSb detector. Figure 2 shows the spectral response of the FBGs described above along with the output spectra of both the 3 μm pump laser and the 3.34 μm RFL when operated at a maximum launched peak pump power of 2.6 W.

Fig. 2. Transmission spectra of the FBGs forming the RFL cavity (red and green curves) along with the output spectra of both the 3 μm pump laser and the 3.34 μm RFL (blue curves) when operated at maximum launched peak pump power of 2.6 W.

The temporal responses of both the 3.34 μm RFL and the 3 μm pump source were characterized at the maximum launched pump peak power of 2.6 W using a fast N2-cooled InSb detector (Judson, J10D-M204-R01M-60). The bandwidth of the detection system was set to 500 kHz giving a response time of 2μs, significantly faster than the 5 ms duration of the QCW pump laser pulse. Figure 3 shows the evolution of both the launched 3 μm pump pulse (blue) and the corresponding 3.34 μm Stokes output pulse (green) at maximum launched pump power.

Fig. 3. Launched pump pulse (blue) and resulting RFL output pulse (green) at maximum launched pump power in QCW operation at 20 Hz and a duty-cycle of 10%.

Note that the curves presented in Fig. 3 represent an average over 19 successive pulses in order to reduce the high frequency laser noise observed in a single pulse. We note that this noise originates from the pump laser, which is operated, as previously mentioned, at the long wavelength edge of the erbium emission band. This might account for its unstable operation but the precise origin of those instabilities is still under investigation.

The laser performances of the RFL were characterized using a low power slow-response thermopile detector (Gentec XLP12-3S-H2) providing a time-averaged output power. The ordinate of Fig. 3 was calibrated by matching the time integral of the pulse profile to the pulse energy, which was evaluated using the thermopile detector. Figure 4 presents the output Stokes average power (left y axis) and Stokes peak power (right y axis) as a function of the launched pump average power. The Stokes average to peak power ratio was evaluated at maximum power.

Fig. 4. Output Stokes average power (left y axis) and corresponding Stokes peak power (right y axis) as a function of the 3 μm launched pump average power when operated in the QCW regime at 20 Hz and 10% duty-cycle.

A maximum average output power of 47 mW is measured, which corresponds to a maximum Stokes peak power of 0.6 W for an averaged launched pump power of 245 mW. When considering the laser threshold of 125 mW, a slope efficiency of 39% with respect to the launched pump power is obtained.

In conclusion, the operation of the first mid-IR RFL has been demonstrated. A single-mode As2S3 ChG RFL emitting at 3.34 μm was demonstrated by using a low-loss Fabry–Pérot cavity formed by a pair of FBGs written in a 3 m long segment of low-loss single-mode As2S3 fiber. A laser output peak power of 0.6 W was achieved at 3.34 μm with a laser efficiency of 39% with respect to the launched pump power provided by a Er-FG fiber laser emitting at 3.005 μm in the QCW regime. This achievement represents an important step toward the development of compact laser sources operating in the mid- to far-IR.

This research was supported by the Canada Excellence Research Chairs (CERC), CorActive High-Tech, Inc., the Natural Science and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), Fonds de recherche du Québec—Nature et technologies (FRQ.NT). The authors thank Dominic Faucher and Yannick Ledemi for their helpful discussions and technical assistance.

References

1.

R. H. Stolen, A. R. Tynes, and E. P. Ippen, Appl. Phys. Lett. 20, 62 (1972). [CrossRef]

2.

V. I. Karpov, E. M. Dianov, V. M. Paramonov, O. I. Medvedkov, M. M. Bubnov, S. L. Semyonov, S. A. Vasiliev, V. N. Protopopov, O. N. Egorova, V. F. Hopin, A. N. Guryanov, M. P. Bachynski, and W. R. L. Clements, Opt. Lett. 24, 887 (1999). [CrossRef]

3.

Y. Feng, L. R. Taylor, and D. B. Calia, Opt. Express 17, 23678 (2009). [CrossRef]

4.

E. M. Dianov, I. A. Bufetov, V. M. Mashinsky, V. B. Neustruev, O. I. Medvedkov, A. V. Shubin, M. A. Melkumov, A. N. Gur’yanov, V. F. Khopin, and M. V. Yashkov, Quantum Electron. 34, 695 (2004). [CrossRef]

5.

V. Fortin, M. Bernier, J. Carrier, and R. Vallée, Opt. Lett. 36, 4152 (2011). [CrossRef]

6.

V. Fortin, M. Bernier, D. Faucher, J. Carrier, and R. Vallée, Opt. Express 20, 19412 (2012). [CrossRef]

7.

G. P. Agrawal, Nonlinear Fiber Optics (Academic, 2001).

8.

S. D. Jackson, Nat. Photonics 6, 423 (2012). [CrossRef]

9.

P. Zhou, X. Wang, Y. Ma, H. Lü, and Z. Liu, Laser Phys. 22, 1744 (2012). [CrossRef]

10.

R. T. White and T. M. Monro, Opt. Lett. 36, 2351 (2011). [CrossRef]

11.

P. Thielen, L. Shaw, J. Sanghera, and I. Aggarwal, Opt. Express 11, 3248 (2003). [CrossRef]

12.

J. S. Sanghera, L. B. Shaw, and I. D. Aggarwal, IEEE J. Sel. Top. Quantum Electron. 15, 114 (2009). [CrossRef]

13.

S. D. Jackson and G. Anzueto-Sánchez, Appl. Phys. Lett. 88, 221106 (2006). [CrossRef]

14.

D. Faucher, M. Bernier, G. Androz, N. Caron, and R. Vallée, Opt. Lett. 36, 1104 (2011). [CrossRef]

15.

M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).

16.

D. Faucher, N. Caron, M. Bernier, and R. Vallée, in Lasers, Sources, and Related Photonic Devices, OSA Technical Digest (OSA, 2012), paper FTh4A.6.

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.3510) Lasers and laser optics : Lasers, fiber
(140.3550) Lasers and laser optics : Lasers, Raman
(230.1480) Optical devices : Bragg reflectors

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: November 9, 2012
Manuscript Accepted: December 4, 2012
Published: January 8, 2013

Citation
M. Bernier, V. Fortin, N. Caron, M. El-Amraoui, Y. Messaddeq, and R. Vallée, "Mid-infrared chalcogenide glass Raman fiber laser," Opt. Lett. 38, 127-129 (2013)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-38-2-127


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References

  1. R. H. Stolen, A. R. Tynes, and E. P. Ippen, Appl. Phys. Lett. 20, 62 (1972). [CrossRef]
  2. V. I. Karpov, E. M. Dianov, V. M. Paramonov, O. I. Medvedkov, M. M. Bubnov, S. L. Semyonov, S. A. Vasiliev, V. N. Protopopov, O. N. Egorova, V. F. Hopin, A. N. Guryanov, M. P. Bachynski, and W. R. L. Clements, Opt. Lett. 24, 887 (1999). [CrossRef]
  3. Y. Feng, L. R. Taylor, and D. B. Calia, Opt. Express 17, 23678 (2009). [CrossRef]
  4. E. M. Dianov, I. A. Bufetov, V. M. Mashinsky, V. B. Neustruev, O. I. Medvedkov, A. V. Shubin, M. A. Melkumov, A. N. Gur’yanov, V. F. Khopin, and M. V. Yashkov, Quantum Electron. 34, 695 (2004). [CrossRef]
  5. V. Fortin, M. Bernier, J. Carrier, and R. Vallée, Opt. Lett. 36, 4152 (2011). [CrossRef]
  6. V. Fortin, M. Bernier, D. Faucher, J. Carrier, and R. Vallée, Opt. Express 20, 19412 (2012). [CrossRef]
  7. G. P. Agrawal, Nonlinear Fiber Optics (Academic, 2001).
  8. S. D. Jackson, Nat. Photonics 6, 423 (2012). [CrossRef]
  9. P. Zhou, X. Wang, Y. Ma, H. Lü, and Z. Liu, Laser Phys. 22, 1744 (2012). [CrossRef]
  10. R. T. White and T. M. Monro, Opt. Lett. 36, 2351 (2011). [CrossRef]
  11. P. Thielen, L. Shaw, J. Sanghera, and I. Aggarwal, Opt. Express 11, 3248 (2003). [CrossRef]
  12. J. S. Sanghera, L. B. Shaw, and I. D. Aggarwal, IEEE J. Sel. Top. Quantum Electron. 15, 114 (2009). [CrossRef]
  13. S. D. Jackson and G. Anzueto-Sánchez, Appl. Phys. Lett. 88, 221106 (2006). [CrossRef]
  14. D. Faucher, M. Bernier, G. Androz, N. Caron, and R. Vallée, Opt. Lett. 36, 1104 (2011). [CrossRef]
  15. M. Bernier, M. El-Amraoui, J. F. Couillard, Y. Messaddeq, and R. Vallée, Opt. Lett. 37, 3900 (2012).
  16. D. Faucher, N. Caron, M. Bernier, and R. Vallée, in Lasers, Sources, and Related Photonic Devices, OSA Technical Digest (OSA, 2012), paper FTh4A.6.

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